CVE-2026-26231: Gitea Authorization Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mm7c-rhg6-qr4r",
  "modified" : "2026-06-16T23:41:01Z",
  "published" : "2026-06-16T23:41:01Z",
  "aliases" : [ "CVE-2026-26231" ],
  "summary" : "Gitea: Authorization Bypass via \"Allow edits from maintainers\" allows unauthorized commits to any readable repo",
  "details" : "## Summary\n\nAny authenticated low-privilege user with read access to a repository can push arbitrary commits directly to that repository, bypassing all write-access checks.\n\n## Vulnerability\n\nGitea's \"Allow edits from maintainers\" PR option can be abused via reverse-fork PRs:\n\n1. The web UI PR-create endpoint binds `allow_maintainer_edit=true` **without** verifying that the submitter has write access to the HEAD repository.\n2. Gitea allows creating a PR where **BASE = attacker's fork** and **HEAD = upstream target**. The attacker is \"maintainer\" of the BASE (their own fork), so the flag is set against the upstream HEAD.\n3. On `git push` over HTTP/SSH, Gitea relaxes the required access mode to `Read` when `SupportProcReceive` is enabled ([`routers/web/repo/githttp.go`](https://github.com/go-gitea/gitea/blob/v1.25.5/routers/web/repo/githttp.go#L189), [`routers/private/serv.go`](https://github.com/go-gitea/gitea/blob/v1.25.5/routers/private/serv.go#L337)) and defers enforcement to the pre-receive hook.\n4. The pre-receive hook calls [`CanMaintainerWriteToBranch`](https://github.com/go-gitea/gitea/blob/v1.25.5/models/issues/pull_list.go#L72) (`models/issues/pull_list.go`), which finds the malicious PR, sees `AllowMaintainerEdit=true`, and checks whether the pusher has write access to the **BASE** repo. Since BASE is the attacker's own fork, the check passes and the push is authorized against the upstream.\n\n## Exploitation\n\n1. Attacker forks the target repository.\n2. Attacker visits the web compare endpoint and creates a PR with `BASE = their_fork`, `HEAD = upstream`, and \"Allow edits from maintainers\" checked.\n3. Attacker clones their fork, makes a commit, and runs `git push <upstream_url> <branch>` — the push is accepted.\n\n## Reproduction\n\n```bash\npython3 poc.py --repo http://gitea:3000/victim/repo --user attacker --password attacker_pass\n```\n[poc.py](https://github.com/user-attachments/files/26641541/poc.py)\n\nExpected output:\n```\n[+] target: victim/my_repo  default branch: main\n[*] forking -> attacker/my_repo_pocfork (202)\n[+] fork ready\n[+] malicious PR created (BASE=attacker fork, HEAD=upstream)\n\nremote: . Processing 1 references\nremote: Processed 1 references in total\nTo http://192.168.101.20:3000/victim/my_repo.git\n   e5c07b3..9a0b884  main -> main\n\n[+] latest commit on victim/my_repo@main: 'PoC: unauthorized commit via maintainer-edit bypass'\n[+] CONFIRMED: unauthorized push to upstream succeeded.\n```\n\nA `PWNED.txt` file will appear on the target repo's default branch, committed by the attacker who has no write access.\n\n\n## Impact\n\nFull repository compromise. Any logged-in user can backdoor any repository they can read, including all public repositories on the instance.\n\n## Suggested Fix\n\nTwo independent checks are missing; both should be added for defense in depth:\n\n1. **At PR creation:** before setting `AllowMaintainerEdit = true`, verify the submitter has write access to the **HEAD** repository.\n2. **In `CanMaintainerWriteToBranch`:** verify that the PR's HEAD repo matches the repository being pushed to, and that the PR was opened by a legitimate owner/writer of the HEAD repository. Do not trust `AllowMaintainerEdit` solely based on BASE write access.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.gitea.io/gitea"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.26.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.26.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/security/advisories/GHSA-mm7c-rhg6-qr4r"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-gitea/gitea"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-16T23:41:01Z",
    "nvd_published_at" : null
  }
}