GHSA-m5ch-ppfx-xv3v CVE-2026-26247 GO-2026-6342

Gitea OAuth2 PKCE S256 verifier bypass

Critical Go

Severity: 9.1 / 10; Critical · CVSS 3.1
Exploit chance (EPSS): 0.50%; Chance of exploitation in the next 30 days. Higher than 42.50% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-284 Improper Access Control
Fix: 1.25.5; Upgrade code.gitea.io/gitea to this version or later

Description

Gitea versions before 1.25.5 do not persist the OAuth2 PKCE S256 challenge method correctly during authorization, allowing token exchange without the expected verifier check.

Affected versions

Go

Package	Vulnerable	Fixed in
code.gitea.io/gitea	`< 1.25.5`	`1.25.5`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

code.gitea.io/gitea Go → `1.25.5`

go

go get code.gitea.io/gitea@v1.25.5 && go mod tidy

Severity breakdown

CVSS 3.1 9.1

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Weakness

CWE-284: Improper Access Control

The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

How to prevent it

Architecture and Design, Operation: Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

References

Advisories

Packages

github.com/go-gitea/gitea

Timeline

Jul 3, 2026 Published
Oct 25, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-rcr6-4jqh-j84m Gitea: Remote Code Execution via diffpatch Git Hook Installation	Critical Known exploited	Also affects code.gitea.io/gitea
GHSA-fq2p-5p22-8g6j Gitea: Public-Only Personal access tokens scope bypass in Organization and Permission Endpoints	Medium	Also affects code.gitea.io/gitea
GHSA-2wm4-vwp6-v7xc Gitea: SSRF via Migration Asset Downloads Bypasses hostmatcher — Reads Internal Files and Cloud Metadata	High	Also affects code.gitea.io/gitea
GHSA-3r5c-2xxx-h872 Gitea: Webhook Authorization Header Returned in Plaintext via API	Low	Also affects code.gitea.io/gitea
GHSA-frpw-3h2q-4jj6 Gitea: Cross-Repo Information Disclosure via Org-Level Actions Run/Job APIs	Medium	Also affects code.gitea.io/gitea
GHSA-q423-49rw-g9mh Gitea: GHSA-8fwc-qjw5-rvgp ClearRepoWatches fix not applied to API EditRepo path — sister code path retains stale watches on public->private	Medium	Also affects code.gitea.io/gitea
GHSA-2fcr-jfvc-vgg2 Gitea: Two SSRF findings	High	Also affects code.gitea.io/gitea
GHSA-fw57-jgch-pgf3 Gitea: ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests	High	Also affects code.gitea.io/gitea

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