DU changed on September 25.

On the evening of Friday, September 25, 2026, Fannie Mae implemented its September update to Desktop Underwriter Version 12.1.¹ Fannie's integration memo, in a preliminary count, put it at 11 new messages, 25 modified and 7 retired.² The update rebuilt the Potential Red Flag section of the findings around occupancy, added a flag that reads external data and the borrower's rental history, let salaried borrowers with twelve months of total work history validate employment after three months in the current job instead of twelve, moved the employment close-by clock from calendar days to business days, and made three conditions return an Ineligible recommendation.¹ As of October 1, the public coverage we could find was one short trade article that names none of those changes,⁵ a blog post derived from it, and two correspondent bulletins that restate or point to Fannie's notes without adding to them.^3,4

This brief walks through every change the way it shows up in the findings — with the mock report, the employment timeline and the close-by calendar you would want in front of you before your next pipeline review. A word on method: every rule below is quoted from the release notes, the integration memo, Fannie Mae's Potential Red Flag matrix dated the same day, and the Selling Guide as published on October 1, 2026. Where Fannie Mae has not said something — what "business days" excludes, which external data feeds the new occupancy flag — the brief says so rather than guessing.

What landed, and which loans it touches

DU releases moved from Saturday evenings to Friday evenings with the June update; Fannie Mae's stated reason was to give partners "additional time to review updates and prepare their systems before normal business hours resume."⁶ So the September update went live on a Friday night, and most lenders would first have seen it on Monday morning.

That matters because the release has two effective-date triggers, and they don't match. Most of it — the red-flag rebuild, the Collateral Underwriter eligibility messages, the new Ineligibles — applies to "DU V. 12.1 loan casefiles submitted or resubmitted on or after the evening of Sept. 25, 2026." The DU validation service changes — the three-month employment rule and the business-day close-by date — apply only to "loan casefiles created on or after Sept. 26, 2026."¹ A file you opened in August and resubmit now gets the new red-flag list and the new Ineligibles, but keeps the old validation rules for as long as it lives. Of the lender bulletins we could find, only Truist's spelled that distinction out.³ Press Resubmit on each sample file below to see which rule set it picks up.

A few smaller items round out the notes and get no section of their own below: a new Observation message on RefiNow transactions "specifying the loan number being refinanced with the transaction," an updated RefiNow project-review message, and a new Observation message "specifying the attachment type provided in the loan application data for cooperative properties and properties in a planned unit development". Fannie also says "various DU messages will be updated" for clarity and consistency with the Selling Guide, without listing them.¹

The red-flag section, rebuilt

The Potential Red Flag section is not new, and the Selling Guide's description of it, last revised in 2022, still lists three message types: excessive resubmissions, a frozen credit report, and potential casefile ID reuse.⁸ The September update moves all three out — the excessive-submission and casefile-reuse messages to the Observation section, the frozen-credit messages to the Verification section — and refills the section with occupancy and collateral.¹

Two existing occupancy verification messages move back in. One existing red flag stays, in a new format. One new occupancy message is added "based on a combination of loan application and external data." One new subject-property message is added based on Collateral Underwriter. Every red flag now renders inside a list message — one for occupancy (Msg 3969), one for the subject property (Msg 3971) — with a Message Identifier that, Fannie notes, "is specific to PRF messaging and is not a DU message ID." And "each instance of a message shown will be factored into the Red Flag counter displayed on the PDF version of the report."¹ The identifiers are DOM-01, DOM-02, DOM-03, OCC-03 and DCM-01; Fannie's two-page matrix, re-issued with the same date, explains what causes each and what it recommends reviewing.⁷

Switch on the signals in a file and watch the section assemble. Flip the layout to see where the same signals surfaced before the update. Tap any identifier for Fannie's own cause and recommended review.

Why occupancy, why now

Fannie Mae's own post-purchase reviews suggest why. In the Quality Insider editions covering April–September 2024, Q1 2025 and Q3–Q4 2025, the top-listed initial significant defect in the random sample was the same each time: misrepresentation of primary occupancy.^11,12,10 In the mid-2024 period, "approximately 25% of the initial significant defects cited … related to income misrepresentation or primary occupancy misrepresentation," and "a common document found in many of these loan files is a fabricated lease agreement."¹¹ In 2025, "the leading driver of PALs across all samples was occupancy - specifically loans delivered as primary residences that were actually investment properties."¹⁰ (A PAL, or price-adjusted loan, has a defect but would still have been deliverable with the correct data and price adjustment.) A significant defect "makes the loan ineligible for delivery to Fannie Mae and requires a remediation. A potential repurchase is possible."¹¹

The incentive is structural. As Fannie puts it, lower-risk transactions "often allow for higher loan-to-value ratios and lower interest rates for the borrower. This cost differential could potentially incentivize the borrower to misrepresent an investment property as a primary residence or second home so they can borrow more at a lower cost."¹³ And the new OCC-03 has an obvious precedent in Fannie's October 2025 red-flag table for owner-occupied files, which lists "Borrower has other rental properties" alongside the insurance policy, the Schedule E and the commute distance.¹³ The June 2026 best practice reads like the message's specification: review "tax returns, bank statements for evidence of rental income, credit history for multiple mortgages, and the homeowner's insurance declaration page for language that suggests the property may be a rental."¹⁰

One caution keeps this honest: application-level alerts and post-purchase findings are different measurements. Cotality's occupancy-fraud risk index fell 5.8% year over year in its 2026 annual report, which says "Cotality's data suggests occupancy fraud risk has plateaued."¹⁴ Its Q2 2026 index still found indications of fraud of some kind in roughly one investment-property application in 44, against one in 119 overall.¹⁵ The performance evidence is older than any of it: a 2023 Philadelphia Fed study of loans originated from 2005 to 2017 found borrowers who misrepresented occupancy defaulted at a 75% higher rate than declared investors and made up about one-third of the effective investor population.¹⁶

OCC-03 is a Fannie Mae flag. We read Freddie Mac's July through October LPA release notes looking for a counterpart; the nearest is a "Primary Residence Review" message that fires when occupancy changes between LPA submissions — closer to DOM-01 than to an external-data flag.¹⁷ Open each document below for what Fannie says to look for in it.

Three months, not twelve

The validation-service change is the one brokers will feel first. Before the update, "DU requires that a borrower have at least 12 months of current employment to validate employment income." Now, for casefiles created on or after Sept. 26, DU requires two things to validate fixed base income: "At least 3 months of current employment" and "At least 12 months of total employment history (current and prior employment combined)." Variable base income, "including borrowers who are paid an hourly or daily wage," still needs 12 months of current employment.¹

Two clarifications the notes don't make. First, the twelve-month rule was never Selling Guide policy. Fannie's own FAQ says so: "The 12-month minimum requirement is specific to the validation service – not a change in overall Selling Guide policy."¹⁸ For a salary documented the standard way rather than validated, the Guide says "a minimum history is not required for inclusion as qualifying income"; for variable base income, "a minimum 12-month history of receiving variable income is required."¹⁹ So the change narrows a gap between DU's validation threshold and the Guide rather than loosening the Guide. Second, "fixed" has a definition: "a set salary or fixed hourly rate with guaranteed minimum hours"; variable is "a fixed hourly rate with fluctuating hours, or an hourly rate that varies."¹⁹ Whether DU's validation logic sorts every hourly-paid borrower into the variable group is not stated. Lenders must still judge whether the work history "reflects a reliable pattern of employment over the most recent two years," with shorter histories acceptable when "positive factors … reasonably offset" them.²⁰

Who this reaches: the Bureau of Labor Statistics' tenure survey, released the day before the DU update, found 20.6% of wage and salary workers had been with their employer a year or less, and 25.5% of 25-to-34-year-olds had 12 months or less.²¹ Those are all workers, not applicants, but they are the population the old threshold excluded from validation. We found no published rationale for the three-month figure; the release notes state it without one.¹ Drag the two histories below and switch the income type.

The close-by clock

When DU validates employment, the findings carry a close-by date: the loan must close by it "to retain relief from representations and warranties on employment verification."¹ For validations based on a verification-of-employment or verification-of-income-and-employment report, that date is now, for casefiles created on or after Sept. 26, "ten business days from the Report Date of the report" — "using business days instead of calendar days."¹ The calendar-day rule it replaces was still on Fannie's FAQ page on October 1, 2026: "the loan must close within ten calendar days of the report date" for an income or employment verification report.¹⁸ Asset-report-based validation is untouched: 15 calendar days from the asset report's date or the next expected deposit date, whichever is later.¹⁸

The change makes DU's clock rhyme with the Selling Guide's own verbal-VOE window, which is in business days: "within 10 business days prior to the note date for employment income."²⁴ Before the update, DU's validation window was the shorter of the two. Pick a report date to see both clocks; if the report date is day zero, the business-day version lands four calendar days later for any weekday report date, and later again when a federal holiday falls in the window and DU skips it. Fannie Mae hasn't said either.

Three new Ineligibles

Three situations that used to produce a reminder, or a problem at delivery, now produce an Ineligible recommendation at submission — and one Ineligible became a keystroke. Two more messages are easy to misread as eligibility hits and aren't. Run each file to see DU's response, then open the cure.

November 30, and the rest of the DU calendar

The findings report many brokers still print is on a clock. With the new PDF findings introduced June 26, Fannie said it would retire the enhanced HTML and enhanced PDF versions "later this year"; the September notes set the date: November 30, 2026.^32,1 The integration memo is blunter: file types 16 and 17 "will be retired on November 30, 2026. Any requests for these Return File Types will result in no response."² The classic HTML version isn't scheduled; the new PDF and the JSON findings are the forward path; the RES, TEXT and XML formats retire October 27, 2028.^2,32

September's update sits inside a busy year for DU 12.1. Scroll the calendar.

What a broker should do now

• Nothing to install. Sponsored brokers reach DU through Desktop Originator, and Fannie Mae deploys the release centrally; the notes' only broker instruction is to "contact their DO sponsoring wholesale lender."^36,1 If you submit through a loan origination system (LOS) or point-of-sale platform, that vendor is working to Fannie's 120-day integration clock.²
• Sort the pipeline by the two triggers. Any DU 12.1 casefile you resubmit from now on gets the new red-flag list, the CU Ineligibles and the rental-income Ineligible. Only casefiles created September 26 or later get the three-month rule and the business-day close-by date.¹ Under the notes' wording, if a borrower with four months on a new salaried job and a year of total history was turned away from validation in August, that file needs a new casefile, not a resubmission.
• Check the occupancy story before DU does. OCC-03 reads "external data" Fannie hasn't described, plus what is on the loan application.⁷ The same story is told by documents you already hold — the REO schedule, Schedule E, the insurance declarations, the credit report — which is where Fannie tells lenders to look.^13,10 If they disagree with the 1003, the flag is the least of it: Fannie's reviewers find the same signals after closing, and occupancy misrepresentation is listed first among significant defects in their random sample.¹⁰
• Know your findings file type. Ask your LOS whether it requests the enhanced HTML or PDF (types 16 and 17) and when it switches to the new PDF or JSON; once those types retire on November 30 the old requests get "no response."²
• Don't wait for Freddie parity. LPA's recent changes went elsewhere — LPA picks up written VOEs as documentation for automated income assessment on October 4, and a primary-residence review message now fires when occupancy changes between submissions — but there is no external-data occupancy flag, no C6 Ineligible and no three-month employment rule in the LPA notes.¹⁷

Frequently asked questions

Sources

Every rule in this brief is quoted from Fannie Mae's release notes, integration memo, Potential Red Flag matrix and Selling Guide as published on October 1, 2026. Some Fannie Mae pages still describe the pre-September rules (ten calendar days; twelve months of current employment) and are cited as such. The sample casefiles, dates and signals in the interactives are illustrative; the message in your own DU findings governs. Where Fannie Mae has not published a detail — what "business days" excludes, which external data feeds OCC-03, the Collateral Underwriter threshold behind DCM-01 — the brief says so. Vendor figures (Cotality, ACES) are labeled as such. Statements about press coverage are as of October 1, 2026.

1. Fannie Mae — Desktop Underwriter/Desktop Originator Release Notes: DU Version 12.1 September Update (July 29, 2026; updated Aug. 31, 2026)Implementation "during the evening of Sept. 25, 2026"; changes apply to casefiles "submitted or resubmitted on or after the evening of Sept. 25, 2026," validation-service changes to casefiles "created on or after Sept. 26, 2026"; Potential Red Flag restructure, example section with DOM-01/02/03, OCC-03, DCM-01, Msg 3969 and 3971, Red Flag counter; CU eligibility messages (lava zones, No Longer Accepted list, C6); fixed base income 3 months current + 12 months total, variable 12 months current; close-by date ten business days from the Report Date; PrincipalResidenceException; subject rental income Ineligible with ADU exception; RefiNow and attachment-type messages; enhanced HTML/PDF findings retired Nov. 30, 2026; brokers "should contact their DO sponsoring wholesale lender."
2. Fannie Mae — DU Version 12.1 Integration Impact Memo: September Update (July 29, 2026)"New Messages 11 | Modified Messages 25 | Retired Messages 7" (the memo calls its table "a preliminary assessment of the anticipated message changes"); DU Spec 1.9.3 adds "PrincipalResidenceException" to DUPolicyFeatureDescription; new JSON container FNMPotentialRedFlagMessageCodes; return file types 16 (enhanced HTML) and 17 (PDF) "will be retired on November 30, 2026. Any requests for these Return File Types will result in no response"; RES/TEXT/XML retiring Oct. 27, 2028; JSON = type 18, new PDF = type 19; vendors must support changes "no later than 120 days after the date the related specifications are made available."
3. Truist Bank Correspondent — Product Release Bulletin COR26-053: DU Version 12.1 Updates (Sept. 25, 2026)Restates the release headings and the two effective-date triggers: "submitted or resubmitted … on or after the evening of September 25, 2026, with the following exception: The DU Validation Service related updates will apply to DU Version 12.1 loan casefiles created on or after September 26, 2026."
4. NewRez Correspondent — Announcement 2026-073: Fannie Mae DU Version 12.1 (Sept. 9, 2026)Summarizes the release headings and points lenders to Fannie Mae's release notes.
5. WRE News — Fannie Mae Updates Desktop Underwriter to Flag Loan Issues Earlier (John G. Stevens, Sept. 25, 2026)The only trade article on the release we found; describes the update in general terms without naming a specific change. Cited as evidence of coverage, not for any rule. An undated Note Servicing Center post, "Fannie Mae updates Desktop Underwriter to flag loan issues sooner," cites this article as its source and adds no detail from the release notes.
6. Fannie Mae — DU Version 12.1 June Update Release Notes (April 29, 2026; updated June 17, 2026)"Going forward, DU updates will move from Saturday evenings to Friday evenings … allows our partners additional time to review updates and prepare their systems before normal business hours resume"; risk and eligibility assessment modification anticipating "a moderate reduction in the number of loan casefiles that receive an Approve/Eligible recommendation" for casefiles created on or after June 27, 2026; UAD 3.6 transition "no later than Nov. 2, 2026."
7. Fannie Mae — Desktop Underwriter Potential Red Flag Messages (9.25.26)Two-page matrix: identifier, message text, "What Causes DU to Return This Message?" and "We Recommend Review of the Following" for DOM-01, DOM-02, DOM-03, OCC-03 and DCM-01; "The appearance of these messages does not affect the underwriting recommendation from DU."
8. Fannie Mae Selling Guide — B3-2-11, DU Underwriting Findings Report (09/07/2022)Describes the report's sections; lists "Excessive resubmissions," "Frozen credit report" and "Potential casefile ID reuse" as the potential red flag messages; "The appearance of these messages does not affect the underwriting recommendation from DU."
9. Fannie Mae — DU Version 11.1 July Update Release Notes (May 29, 2024)"Potential Red Flag Occupancy Message — A new message will be issued reminding lenders to confirm the accuracy of the occupancy on the loan casefile. This message will be issued when the loan is submitted as an investment property and later changed to a primary residence." Effective the weekend of July 20, 2024.
10. Fannie Mae — Quality Insider: Understand Top Defects to Help Strengthen Loan Quality (June 29, 2026)Top 10 initial significant defects, Q3–Q4 2025 random sample, led by "Misrepresentation of primary occupancy"; "In 2025, the leading driver of PALs across all samples was occupancy"; defect definition citing "rent loss coverage"; holistic-review best practice (tax returns, bank statements, credit history for multiple mortgages, insurance declaration page); "Appraisal-related issues made up four of the top ten findings"; definition of a price-adjusted loan (PAL).
11. Fannie Mae — Quality Insider: Understand Top Defects to Help Strengthen Loan Quality (January 2025)Random sample of loans acquired April–September 2024 led by "Misrepresentation of Primary Occupancy"; "Approximately 25% of the initial significant defects cited … related to income misrepresentation or primary occupancy misrepresentation"; "A common document found in many of these loan files is a fabricated lease agreement"; "Significant Defect: A loan manufacturing error that makes the loan ineligible for delivery to Fannie Mae and requires a remediation. A potential repurchase is possible."
12. Fannie Mae — Quality Insider: Understand Top Defects to Help Strengthen Loan Quality (September 2025)Q1 2025 random sample led by "Misrepresentation of primary occupancy."
13. Fannie Mae — Quality Insider: Getting It Right – Reverification of Occupancy (October 2025)Cost-differential incentive language; red-flag tables for owner-occupied, second-home and investment files, including "Borrower has other rental properties," "Property insurance policy is inconsistent with occupancy type," "Schedule E … reflects the subject property as a rental property," "Occupant field on appraisal reflects tenant or vacant," "Significant or unrealistic commuting distance."
14. Cotality — 2026 Annual Fraud Report (Sept. 15, 2026; vendor-modeled alert index)"Occupancy risk decreased 5.8% compared to a year ago"; "Cotality's data suggests occupancy fraud risk has plateaued"; "The most common occupancy fraud is that of an investor claiming primary occupancy on a subject property."
15. Cotality — Q2 2026 Mortgage Application Fraud Risk Index (Aug. 4, 2026; vendor-modeled)Index 132, up 9.1% from Q1 and down 4.6% year over year; "1 in 119 mortgage applications had indications of fraud"; "1 in 44 investment applications"; "1 in 27 multi-family applications."
16. Federal Reserve Bank of Philadelphia — Working Paper 23-01, Owner-Occupancy Fraud and Mortgage Performance (Elul, Payne, Tilson; January 2023)Fraudulent borrowers "defaulting at a 75 percent higher rate" than declared investors and "one-third of the effective investor population"; "17 percent of declared owner-occupants have multiple first liens in their credit bureau files four quarters following mortgage origination, compared with 42 percent of declared investors"; 584,499 loans, 2005–2017.
17. Freddie Mac — Loan Product Advisor Release Notes, October 2026 (posted Sept. 16, 2026) and August 2026 (posted July 15, 2026)August notes: "Primary Residence Review Message Updates — Effective August 23, 2026 — We're revising a message to help you identify if there has been a change in the borrower's primary residence information" (new message effective July 26). October notes: "Written Verification of Employment (VOE) Enhancement — Effective October 4, 2026 — Guide Bulletin 2026-12 announced that written VOE has been added as eligible documentation for an automated income assessment"; no external-data occupancy flag, C6 Ineligible or employment-tenure change. August notes: sf.freddiemac.com/docs/pdf/lpa-august-2026-release-notes.pdf.
18. Fannie Mae — DU Validation Service: Frequently Asked Questions (FAQs updated November 2025; as published Oct. 1, 2026)Pre-September rules, still posted: "When employment is validated, the loan must close within ten calendar days of the report date for an income or employment verification report or within 15 calendar days using a 12-month asset verification report"; asset-report close-by "15-days from the asset verification report date, or up to the next expected deposit date … (whichever is greater)"; "DU requires at least 12 months of income for the validation service to run. The 12-month minimum requirement is specific to the validation service – not a change in overall Selling Guide policy."
19. Fannie Mae Selling Guide — B3-3.3-01, Base Income (03/04/2026)"Fixed base income refers to a set salary or fixed hourly rate with guaranteed minimum hours"; "Variable base income refers to a fixed hourly rate with fluctuating hours, or an hourly rate that varies"; fixed base income: "A minimum history is not required for inclusion as qualifying income"; variable base income: "A minimum 12-month history of receiving variable income is required." (The income chapter was restructured by SEL-2026-02, which created the section defining fixed and variable base income.)
20. Fannie Mae Selling Guide — B3-3.2-02, Standards for Employment-Related Income (03/04/2026)"Lenders must evaluate the borrower's work history to determine whether it reflects a reliable pattern of employment over the most recent two years. A shorter employment history may be considered eligible for qualifying purposes if the borrower's employment profile includes positive factors that reasonably offset the shorter employment history."
21. U.S. Bureau of Labor Statistics — Employee Tenure in 2026 (USDL-26-1532, Sept. 24, 2026)Median tenure 4.1 years in January 2026; "the share of wage and salary workers with a year or less of tenure with their current employer was 20.6 percent"; ages 25 to 34 median 3.0 years; Table 3: 25.5% of workers aged 25–34 with 12 months or less of tenure (bls.gov/news.release/tenure.t03.htm). Covers all wage and salary workers, not mortgage applicants.
22. ACES Quality Management — Q1 2026 Mortgage QC Industry Trends Report (vendor QC benchmarking)Critical defect rate 1.71%; income/employment 20.07% of critical defects; borrower/mortgage eligibility 7.43%; appraisal 3.35%.
23. Fannie Mae Selling Guide — B3-2-02, DU Validation Service (02/05/2025)"When employment is validated by DU, the validation satisfies the requirement for verbal verification of employment … Lenders must comply with all DU messages, including ensuring the loan closes by the 'Close by Date' stated in the DU employment validation message"; lender must "investigate and resolve any conflicting or contradictory information"; relief from representations and warranties on validated components.
24. Fannie Mae Selling Guide — B3-3.1-04, Verbal Verification of Employment (03/04/2026)"The verbal VOE must be obtained within 10 business days prior to the note date for employment income, and within 120 calendar days prior to the note date for self-employment income"; "When employment is validated by DU … The DU message will include a date by which the loan must close."
25. Fannie Mae Selling Guide — B3-3.8-01, General Rental Income Information, and B3-3.8-02, Rental Income from the Subject Property (09/02/2026)"Generally, rental income from the borrower's principal residence (a one-unit principal residence or the unit the borrower occupies in a two- to four-unit property) or a second home cannot be used to qualify the borrower. However, Fannie Mae does allow certain exceptions … for boarder income and rental income on principal residence properties with accessory units"; ADU limitations: one existing ADU, purchase or limited cash-out refinance only, "limited to 30% of the total qualifying income" (B3-3.8-02). Formerly B3-3.1-08.
26. Fannie Mae Selling Guide — B2-1.1-01, Occupancy Types (10/05/2022)Principal-residence exceptions for "Parents or legal guardian wanting to provide housing for their handicapped or disabled adult child" and "Children wanting to provide housing for parents" ("If the parent is unable to work or does not have sufficient income to qualify for a mortgage on their own, the child is considered the owner/occupant"); second-home footnote: rental income permitted "as long as the income is not used for qualifying purposes."
27. Fannie Mae Selling Guide — B4-1.3-06, Property Condition and Quality of Construction of the Improvements (06/04/2025)"Loans secured by properties with a condition rating of C6 are not eligible for sale to Fannie Mae. Any deficiencies impacting the safety, soundness, or structural integrity of the property must be repaired with a resulting minimum condition rating of C5 prior to sale of the loan"; C6 appraisals "must be completed 'subject to' completion of the deficient item(s)."
28. Fannie Mae Selling Guide — B4-1.3-12, Appraisal Quality Matters (09/03/2025), and Appraiser Quality Monitoring FAQs (March 2025)"Fannie Mae may notify a lender that appraisals prepared by a given appraiser are no longer accepted … the lender is prohibited from delivering mortgages to Fannie Mae secured by properties appraised by that individual"; AQM FAQs: the list "includes appraisers whose work is subject to 100% post-acquisition review or is no longer accepted by Fannie Mae," updated monthly, enforced via a UCDP message (singlefamily.fanniemae.com/media/16536/display).
29. Fannie Mae Selling Guide — B2-3-04, Special Property Eligibility Considerations (10/08/2025)"Fannie Mae will only purchase or securitize mortgage loans secured by properties that are located within lava zones 3 through 9 on the island of Hawaii. Properties in lava zones 1 and 2 are not eligible due to the increased risk of property destruction from lava flows within these areas."
30. Fannie Mae — Collateral Underwriter: Risk Score and Risk Flags Overview (job aid) and Collateral Underwriter product page"Each appraisal receives a score on a scale of 1.0 to 5.0, with 1 indicating the lowest risk and 5 indicating the highest risk"; "Overvaluation - Statistical modeling is used to identify appraisals with higher probability of material overvaluation"; "a high-risk score does not necessarily mean the appraisal is bad"; product page: relief on property value "with CU risk scores of 2.5 or lower as part of Day 1 Certainty" (singlefamily.fanniemae.com/applications-technology/collateral-underwriter).
31. Fannie Mae — Quality Insider: Understand Top Defects to Help Strengthen Loan Quality (May 2024)"Loans with appraisal related significant defects presented the following high-risk flags: Had a median CU score of 4.6; ~95% had an Overvaluation Flag (OVF)."
32. Fannie Mae — New DU Underwriting Findings Report Options Release Notes (May 27, 2026; updated June 15, 2026)New PDF findings "on the evening of June 26, 2026," optional and requested through the LOS; "We plan to retire the enhanced HTML and enhanced PDF versions later this year"; "We will retire the RES, TEXT, and XML formats on October 27, 2028 … as part of their 2026/2027 roadmap."
33. Fannie Mae — DU Version 12.1 Release Notes (Jan. 28, 2026; updated Feb. 18, 2026; effective the weekend of March 21, 2026)DU 12.1 implementation; ADU rental income "on one-unit, principal residence, purchase and limited cash-out refinance transactions," with the 30%-of-qualifying-income test; HomeStyle Refresh; DU 11.1 retirement.
34. Fannie Mae — Lender Letter LL-2026-06, VantageScore 4.0 Broad Lender Availability (Sept. 9, 2026; updated Sept. 30, 2026), and DU Version 12.1 VantageScore 4.0 Update Release Notes (Sept. 9, 2026)VantageScore 4.0 expanded "to all Fannie Mae-approved lenders, without prior written approval"; "the same credit score model must be used for all borrowers on a single loan"; Special Feature Code 067; DU release notes: "DU has been updated to permit credit reports containing VantageScore® 4.0 for all loan casefiles underwritten through Desktop Underwriter® (DU®) Version 12.1" (release notes).
35. Fannie Mae — DU for Government Loans Release Notes: September 2026 Release (Aug. 26, 2026)Updated "during the weekend of Sept. 26, 2026": FHA message updates and "DU will now use the lender-provided qualifying rate on all ARMs."
36. Fannie Mae — Desktop Underwriter & Desktop Originator (product page)"Sponsored mortgage brokers have access to DU through Desktop Originator (DO)."