CVE-2025-40918
📋 TL;DR
This vulnerability in Authen::SASL::Perl::DIGEST_MD5 generates client nonces (cnonce) with insufficient entropy, using predictable values like PID, epoch time, and Perl's non-cryptographic rand function. This weakens mutual authentication in SASL DIGEST-MD5, potentially allowing chosen plaintext attacks. Systems using affected Perl modules for authentication are vulnerable.
💻 Affected Systems
- Authen::SASL::Perl::DIGEST_MD5 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
Authentication bypass or session hijacking through predictable cnonce values enabling chosen plaintext attacks against DIGEST-MD5 authentication.
Likely Case
Reduced authentication security making brute-force or replay attacks more feasible against systems using vulnerable SASL implementations.
If Mitigated
Minimal impact if systems use alternative authentication mechanisms or have additional security controls like network segmentation.
🎯 Exploit Status
Exploitation requires understanding of SASL DIGEST-MD5 protocol and ability to predict or influence cnonce generation. No public exploits known at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1900
Vendor Advisory: https://security.metacpan.org/patches/A/Authen-SASL/2.1800/CVE-2025-40918-r1.patch
Restart Required: No
Instructions:
1. Update Authen::SASL Perl module to version 2.1900 or later using CPAN: 'cpan Authen::SASL' 2. Alternatively, apply the security patch from the vendor advisory URL to existing installations.
🔧 Temporary Workarounds
Disable DIGEST-MD5 authentication
allConfigure applications to use alternative SASL mechanisms like CRAM-MD5, PLAIN (with TLS), or GSSAPI instead of DIGEST-MD5.
# Configure your application's SASL settings to exclude DIGEST-MD5
🧯 If You Can't Patch
- Implement network segmentation to isolate systems using vulnerable authentication
- Enable additional authentication factors or implement rate limiting on authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check Perl module version: 'perl -MAuthen::SASL -e "print $Authen::SASL::VERSION"' and verify if between 2.04 and 2.1800.Check Version:
perl -MAuthen::SASL -e "print $Authen::SASL::VERSION"Verify Fix Applied:
After update, verify version is 2.1900 or higher using same command, and check that DIGEST_MD5.pm line 263 no longer uses insecure rand/PID/time combination.📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts with predictable patterns
- Unusual authentication timing or repeated attempts
Network Indicators:
- SASL DIGEST-MD5 authentication traffic with suspicious cnonce patterns
SIEM Query:
Authentication logs showing repeated SASL DIGEST-MD5 failures or successful authentications with similar timing patterns🔗 References
- https://datatracker.ietf.org/doc/html/rfc2831
- https://github.com/gbarr/perl-authen-sasl/pull/22
- https://metacpan.org/dist/Authen-SASL/source/lib/Authen/SASL/Perl/DIGEST_MD5.pm#L263
- https://metacpan.org/release/EHUELS/Authen-SASL-2.1900/changes
- https://security.metacpan.org/patches/A/Authen-SASL/2.1800/CVE-2025-40918-r1.patch
- http://www.openwall.com/lists/oss-security/2025/07/16/5
