Gitea: TOTP TOCTOU race on web 2FA paths + missing replay check on Basic-Auth X-Gitea-OTP surface

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N

EPSS

• CVE-2026-20779: 0.49% estimated exploitation activity in the next 30 days; percentile 42.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary I'm reporting two related TOTP one-time-use defects in Gitea that survive the CVE-2021-45331 fix. The 2018 fix (PR #3878) introduced the TwoFactor.LastUsedPasscode field and added an in-memory inequality check on the web 2FA login path. That check works correctly in the single-request case, but it leaves two follow-up gaps: 1. A TOCTOU race on the web surfaces (Defect 1). The read-validate-check-save sequence against the twofactor row is not atomic. Two parallel submissions of the same passcode each load their own in-memory copy where LastUsedPasscode still holds the prior value; both pass the inequality check, both authenticate, and both then write the same new value back. Net effect: the same OTP redeems for two independent logged-in sessions. 2. No LastUsedPasscode check at all on the Basic-Auth API surface (Defect 2). services/auth/basic.go calls twofa.ValidateTOTP(...) for X-Gitea-OTP without ever reading or writing LastUsedPasscode. The same six-digit code is replayable…

Published by the source

21 Jul 2026, 21:57 UTC

Last modified by the source

21 Jul 2026, 21:57 UTC

Source last checked

26 Oct 2026, 15:27 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-gx3v-q759-g323

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# Patch Next advisory brief: CVE-2026-20779

Advisory: Gitea: TOTP TOCTOU race on web 2FA paths + missing replay check on Basic-Auth `X-Gitea-OTP` surface
IDs: CVE-2026-20779, GHSA-gx3v-q759-g323
Record: https://patchnext.com/advisories/cve-2026-20779 (revision 1, source checked 26 Oct 2026, 15:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: code.gitea.io/gitea 1.26.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go code.gitea.io/gitea: affected >= 1.5.0, < 1.26.3; fixed in 1.26.3

## Suggested inspection (read-only)
- Go code.gitea.io/gitea: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on code.gitea.io/gitea.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-gx3v-q759-g323 (GitHub-reviewed advisory GHSA-gx3v-q759-g323 lists affected ranges: Go code.gitea.io/gitea >=1.5.0 <1.26.3)

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