Gitea: SSRF in restore-repo via unsanitized pull_request.yml Head.CloneURL

Summary

Gitea's restore-repo CLI command restores a repository from a dump directory/archive. When parsing pull_request.yml from that dump, the Head.CloneURL field is used to add a git remote and fetch from it with no validation, because the safety check that's supposed to guard it (CheckAndEnsureSafePR) is called with an empty commonCloneBaseURL, which silently disables it. This lets a malicious dump make the Gitea server execute git fetch against an attacker-chosen URL (SSRF), or disclose a local git repository via file://. This is a different root cause from the recently fixed path-traversal issue in the same command (#38215), which patched DownloadURL/PatchURL but not Head.CloneURL.

Details

services/migrations/restore.go's GetPullRequests() unmarshals pull_request.yml directly into base.PullRequest structs with no validation of Head.CloneURL:

err = yaml.Unmarshal(bs, &pulls)
...
for _, pr := range pulls {
    if pr.PatchURL != "" {
        pr.PatchURL = "file://" + util.FilePathJoinAbs(r.baseDir, pr.PatchURL)
    }
    CheckAndEnsureSafePR(pr, "", r)   // <-- empty baseURL
}

CheckAndEnsureSafePR (services/migrations/common.go) is supposed to reject Head.CloneURL/PatchURL values that don't share a common base URL:

func hasBaseURL(toCheck, baseURL string) bool {
    if len(baseURL) > 0 && baseURL[len(baseURL)-1] != '/' {
        baseURL += "/"
    }
    return strings.HasPrefix(toCheck, baseURL)
}

func CheckAndEnsureSafePR(pr *base.PullRequest, commonCloneBaseURL string, g base.Downloader) bool {
    valid := true
    if pr.PatchURL != "" && !hasBaseURL(pr.PatchURL, commonCloneBaseURL) {
        pr.PatchURL = ""
        valid = false
    }
    if pr.Head.CloneURL != "" && !hasBaseURL(pr.Head.CloneURL, commonCloneBaseURL) {
        pr.Head.CloneURL = ""
        valid = false
    }
    return valid
}

strings.HasPrefix(anything, "") is always true in Go. Because restore.go is the only caller that passes "" as commonCloneBaseURL, this check is a complete no-op on the restore-repo path — Head.CloneURL survives unchanged regardless of its value. Every other downloader (github.go, gitlab.go, gitea_downloader.go, codebase.go, codecommit.go, onedev.go) passes a real base URL, so they are not affected.

services/migrations/gitea_uploader.go then uses the unvalidated value directly:

err := g.gitRepo.AddRemote(remote, pr.Head.CloneURL, true)
// ... later: fetch from that remote

resulting in the server executing git fetch against an attacker-controlled URL sourced from the dump file.

RCE via git's ext:: transport helper was tested and ruled out — a normal git install rejects it by default (fatal: transport 'ext' not allowed), independent of Gitea's own configuration. This report is scoped to SSRF and local git-repository disclosure.

Confirmed present, byte-for-byte identical, in v1.26.4 (latest stable tag), release/v1.27, and main, by direct checkout and diff.

PoC

1. Create a dump directory following the normal restore-repo layout (repo.yml, etc.), and add a pull_request.yml containing at least one entry with:

   - number: 1
     head:
       cloneURL: "http://<attacker-controlled-or-internal-host>:<port>/ssrf-proof"
       ref: "main"

2. Run gitea restore-repo against that dump directory for any repo owner.
3. Observe on the target host/listener: an actual git HTTP discovery request arrives, e.g. GET /ssrf-proof/info/refs?service=git-upload-pack, driven entirely by the value from the dump file.

Verified the core mechanism (steps 2–3, i.e. the unvalidated Head.CloneURL surviving CheckAndEnsureSafePR("") and then being used in a real git remote add + git fetch) with a minimal, standalone Go program built from the verbatim, unmodified hasBaseURL / CheckAndEnsureSafePR function bodies (attached: gitea_ssrf_poc.go), run end-to-end against a local HTTP listener. The listener's access log confirms the request actually arrives.

Impact

An attacker who can get an administrator to run gitea restore-repo against a malicious dump (the same threat model already accepted for the just-fixed path-traversal issue in this command, #38215) can make the Gitea server issue a git fetch against an arbitrary attacker-chosen URL. This allows:

• SSRF against internal-only services or cloud metadata endpoints reachable from the Gitea host.
• Disclosure of local git repositories reachable via file:// paths readable by the Gitea process.

No public disclosure planned. Happy to provide further detail on request.