Gogs user can update repository content with read-only permission

Vulnerability Description

The endpoint PUT /repos/:owner/:repo/contents/* does not require write permissions and allows access with read permission only via repoAssignment().

After passing the permission check, PutContents() invokes UpdateRepoFile(), which results in:

• Commit creation
• Execution of git push

As a result, a token with read-only permission can be used to modify repository contents.

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Attack Prerequisites

• Possession of a valid access token
• Read permission on the target repository (public repository or collaborator with read access)

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Attack Scenario

1. The attacker accesses the target repository with a read-only token
2. The attacker sends a PUT /contents request to update an arbitrary file
3. The server creates a commit and performs a git push on behalf of the attacker

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Potential Impact

• Source code tampering
• Injection of backdoors
• Compromise of release artifacts and distributed packages