Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability in Gitea's OAuth2 implementation could allow an attacker to reuse an existing access token to obtain new tokens, effectively extending access beyond its intended expiration. This could potentially grant unauthorized persistent access to systems that rely on Gitea for authentication.
- Access tokens can be reused for extended access.
- Critical to confirm if Gitea is used for authentication.
- Verify Gitea usage to understand potential exposure.
Attack Path
How an attacker could exploit the issue
An attacker can exploit this vulnerability by sending a crafted request to the OAuth2 token endpoint. If the attacker possesses an unexpired access token for the same OAuth2 application, they can submit it with a `refresh_token` grant type. Although the system verifies the signature and grant, it fails to confirm if the token is actually a refresh token. This allows an attacker to effectively renew their access, gaining extended privileges beyond the original token's intended lifespan.
- Publicly accessible token endpoint.
- Submitting an access token as a refresh token.
- Extended access beyond token lifetime.
Live Threat
Current exploitation, exposure, and threat context
An unexpired access token could be misused to obtain new, longer-lasting tokens, allowing unauthorized continued access to the OAuth2 application. This could occur when an attacker gains possession of a valid access token and uses it to refresh their session beyond its intended expiration. The primary risk involves the extended, unauthorized use of application resources.
- Access to OAuth2 application resources.
- Misused access token to obtain new tokens.
- Continued unauthorized access to services.
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability in Gitea's OAuth2 token endpoint impacts services that use this functionality for authentication and access control. Application owners and platform teams are likely responsible for addressing this, as they manage the Gitea instances and their integrations. The immediate priority is to identify all deployed Gitea instances, assess their exposure, and determine if they are handling sensitive data or critical business functions before planning remediation.
- Application owners should own the issue.
- Verify OAuth2 token endpoint exposure.
- Plan remediation based on identified risk.
