CVE-2026-28699 in Gitea
Summary
by MITRE • 07/04/2026
Gitea versions up to and including 1.26.1 allow OAuth2 access token scope enforcement to be bypassed through HTTP Basic authentication.
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Analysis
by VulDB Data Team • 07/04/2026
This vulnerability in Gitea versions up to 1.26.1 represents a critical authorization flaw that undermines the security controls designed to protect user resources through OAuth2 scope enforcement mechanisms. The issue arises from an improper implementation where HTTP Basic authentication can be used to bypass the intended access control restrictions that should limit what actions a token can perform within the system. When users authenticate using HTTP Basic authentication instead of the expected OAuth2 flow, the system fails to properly validate the token scopes, allowing unauthorized access to resources that should be restricted based on the original scope assignment.
The technical implementation flaw stems from how Gitea processes authentication requests and validates access tokens across different authentication methods. Specifically, when an attacker or legitimate user submits credentials through HTTP Basic authentication, the system does not perform the same scope validation checks that would normally occur during OAuth2 token validation. This creates a path where users can escalate their privileges or access restricted functionality simply by changing the authentication method rather than properly authenticating with the intended OAuth2 token. The vulnerability exists because the authentication pipeline does not maintain consistent security state validation between different authentication mechanisms.
The operational impact of this vulnerability is significant as it allows for privilege escalation attacks and potential data exposure across multiple user accounts and repositories within the Gitea instance. An attacker who gains access to a valid OAuth2 token could potentially use HTTP Basic authentication methods to bypass scope restrictions, accessing resources or performing actions that exceed the original token permissions. This affects all users of affected Gitea versions and could lead to unauthorized code access, repository modifications, data leakage, or further exploitation within the system environment. The vulnerability particularly impacts organizations that rely on OAuth2 for secure application integration and user authentication where scope enforcement is critical for maintaining proper access control boundaries.
Organizations should immediately upgrade to Gitea version 1.26.2 or later where this vulnerability has been addressed through proper authentication method validation and consistent scope enforcement across all authentication pathways. The fix typically involves implementing stricter checks that ensure OAuth2 token scopes are properly validated regardless of whether authentication occurs through standard OAuth2 flows or HTTP Basic authentication methods. System administrators should also review existing access logs for potential unauthorized activities and consider implementing additional monitoring controls to detect unusual authentication patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-284 Access Control Issues and can be categorized under ATT&CK technique T1078 Valid Accounts, as it exploits legitimate authentication mechanisms to gain elevated privileges through scope bypass rather than brute force or credential theft attacks.
The root cause of this issue demonstrates a fundamental flaw in how Gitea handles authentication state management and access control validation. The system should maintain consistent security policies regardless of the authentication method used, ensuring that OAuth2 token scopes are enforced uniformly across all access paths. Proper implementation requires that any authentication attempt undergoes identical scope validation checks to prevent attackers from exploiting method switching as a bypass mechanism. Organizations implementing similar systems should establish robust testing procedures that validate access control behavior under various authentication scenarios and ensure that security policies remain consistent regardless of the entry point used for authentication requests.