CVE-2025-40916
📋 TL;DR
CVE-2025-40916 is a cryptographic weakness in Mojolicious::Plugin::CaptchaPNG version 1.05 for Perl, where the captcha generation uses the insecure rand() function instead of cryptographically secure random number generation. This allows attackers to predict or brute-force captcha values, potentially bypassing security controls that rely on captcha protection. Any web application using this vulnerable plugin version is affected.
💻 Affected Systems
- Mojolicious::Plugin::CaptchaPNG
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Attackers bypass captcha protection entirely, enabling automated attacks like account takeover, credential stuffing, spam registration, or brute-force attacks on login forms.
Likely Case
Automated bots successfully bypass captcha on forms, leading to spam submissions, unauthorized account creation, or automated attacks on authentication endpoints.
If Mitigated
With proper monitoring and rate limiting, impact is reduced to occasional successful bypasses rather than complete system compromise.
🎯 Exploit Status
Exploitation requires understanding of Perl's rand() predictability and ability to generate matching captcha values.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.06
Vendor Advisory: https://metacpan.org/release/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.06/changes
Restart Required: Yes
Instructions:
1. Update Perl module: cpanm Mojolicious::Plugin::CaptchaPNG@1.06
2. Restart your Mojolicious application
3. Verify the update with: perl -MMojolicious::Plugin::CaptchaPNG -e 'print $Mojolicious::Plugin::CaptchaPNG::VERSION'
🔧 Temporary Workarounds
Replace with alternative captcha solution
allTemporarily disable vulnerable plugin and implement alternative captcha mechanism
# Remove from Mojolicious app configuration
# Implement alternative like reCAPTCHA or custom secure solution
🧯 If You Can't Patch
- Disable captcha functionality entirely and implement alternative rate limiting or authentication controls
- Implement additional server-side validation and monitoring for suspicious captcha bypass patterns
🔍 How to Verify
Check if Vulnerable:
Check installed Perl module version: perl -MMojolicious::Plugin::CaptchaPNG -e 'print $Mojolicious::Plugin::CaptchaPNG::VERSION'Check Version:
perl -MMojolicious::Plugin::CaptchaPNG -e 'print $Mojolicious::Plugin::CaptchaPNG::VERSION'Verify Fix Applied:
Verify version is 1.06 or higher using the same command, and confirm captcha generation uses secure random source by reviewing application logs or testing captcha predictability📡 Detection & Monitoring
Log Indicators:
- Unusually high success rates on captcha-protected forms
- Multiple failed captcha attempts followed by sudden success patterns
- Automated traffic patterns on protected endpoints
Network Indicators:
- High volume of requests to captcha-protected endpoints from single IPs
- Predictable timing between captcha generation and submission attempts
SIEM Query:
source=web_logs (endpoint="/login" OR endpoint="/register") status=200 | stats count by ip, user_agent | where count > threshold🔗 References
- https://metacpan.org/pod/perlfunc#rand
- https://metacpan.org/release/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.04/diff/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.05/lib/Mojolicious/Plugin/CaptchaPNG.pm
- https://metacpan.org/release/GRYPHON/Mojolicious-Plugin-CaptchaPNG-1.06/changes
- https://security.metacpan.org/docs/guides/random-data-for-security.html
