CVE-2025-40929
📋 TL;DR
CVE-2025-40929 is an integer buffer overflow vulnerability in Cpanel::JSON::XS Perl module versions before 4.40. When parsing malicious JSON input, it causes a segmentation fault, enabling denial-of-service attacks against applications using this library. Any Perl application using vulnerable versions of Cpanel::JSON::XS for JSON parsing is affected.
💻 Affected Systems
- Cpanel::JSON::XS Perl module
⚠️ 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
Complete service disruption through denial-of-service, potential remote code execution if the segfault can be weaponized (though unspecified in advisory), and system instability.
Likely Case
Denial-of-service causing application crashes when processing malicious JSON input, leading to service interruptions.
If Mitigated
Minimal impact if proper input validation and rate limiting are implemented, though the vulnerability remains present.
🎯 Exploit Status
Exploitation requires crafting specific JSON input that triggers the integer overflow. No public exploit code is available as of the advisory date.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.40
Vendor Advisory: https://metacpan.org/release/RURBAN/Cpanel-JSON-XS-4.40/changes
Restart Required: No
Instructions:
1. Update Cpanel::JSON::XS to version 4.40 or later using CPAN: 'cpan install Cpanel::JSON::XS'
2. Alternatively, update via package manager if using system packages
3. Verify the update with 'perl -MCpanel::JSON::XS -e "print $Cpanel::JSON::XS::VERSION"'
🔧 Temporary Workarounds
Input validation and sanitization
allImplement strict input validation to reject malformed JSON before it reaches the vulnerable parser
Rate limiting JSON parsing
allLimit the rate at which JSON parsing requests are processed to reduce DoS impact
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block malformed JSON patterns
- Isolate vulnerable services behind reverse proxies with request filtering
🔍 How to Verify
Check if Vulnerable:
Check the installed version of Cpanel::JSON::XS. If version is less than 4.40, the system is vulnerable.Check Version:
perl -MCpanel::JSON::XS -e "print $Cpanel::JSON::XS::VERSION"Verify Fix Applied:
After updating, verify the version shows 4.40 or higher and test JSON parsing functionality.📡 Detection & Monitoring
Log Indicators:
- Segmentation fault errors in application logs
- Unexpected process termination of Perl applications
- High frequency of JSON parsing failures
Network Indicators:
- Unusual patterns of JSON payloads to application endpoints
- Increased error responses from JSON APIs
SIEM Query:
source="application.log" AND ("segmentation fault" OR "segfault" OR "SIGSEGV") AND process="perl"🔗 References
- https://github.com/rurban/Cpanel-JSON-XS/commit/378236219eaa35742c3962ecbdee364903b0a1f2.patch
- https://metacpan.org/release/RURBAN/Cpanel-JSON-XS-4.39/source/XS.xs#L713
- https://metacpan.org/release/RURBAN/Cpanel-JSON-XS-4.40/changes
- http://www.openwall.com/lists/oss-security/2025/09/08/1
- https://lists.debian.org/debian-lts-announce/2025/09/msg00034.html
