Access token theft via skipped S256 session persistence
Published Jul 3, 2026 · Updated Jul 3, 2026
Authentication bypass in Gitea before 1.25.5 allows remote attackers to obtain OAuth2 access tokens through a PKCE S256 exchange. In AuthorizeOAuth, the S256 switch case exits without storing CodeChallengeMethod in the session, so the grant omits it and the token endpoint skips verifier validation. Exploitation requires an OAuth2 authorization flow using PKCE S256 and a redeemable authorization code; the resulting token carries the grant's authorized scopes.
Summary
What happened
Authentication bypass in Gitea before 1.25.5 allows remote attackers to obtain OAuth2 access tokens through a PKCE S256 exchange. In AuthorizeOAuth, the S256 switch case exits without storing CodeChallengeMethod in the session, so the grant omits it and the token endpoint skips verifier validation. Exploitation requires an OAuth2 authorization flow using PKCE S256 and a redeemable authorization code; the resulting token carries the grant's authorized scopes.
The record
- CVE
- CVE-2026-26247
- Published
- Jul 3, 2026
- Updated
- Jul 3, 2026
- Vendor
- Gitea
- Product
- Gitea
- Classifications
- CWE-284, T1528
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 3, 2026CVE publishedPublication date reported by the CVE source.
- Jul 3, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <1.25.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
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Your stack
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