CVE-2020-16154
📋 TL;DR
CVE-2020-16154 is a signature verification bypass vulnerability in App::cpanminus (cpanm) for Perl. It allows attackers to install malicious CPAN modules by bypassing cryptographic signature checks. This affects systems using cpanm version 1.7044 to install Perl modules.
💻 Affected Systems
- App::cpanminus (cpanm)
📦 What is this software?
\ by App\
Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Attackers could install backdoored Perl modules that execute arbitrary code, leading to complete system compromise, data theft, or lateral movement.
Likely Case
Supply chain attack where attackers compromise CPAN mirrors or intercept downloads to install malicious modules with elevated privileges.
If Mitigated
Limited to module installation failures or requiring manual verification of module sources if proper network controls exist.
🎯 Exploit Status
Exploitation requires ability to manipulate module downloads or compromise CPAN mirrors. Public proof-of-concept demonstrates signature bypass.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.7045 and later
Vendor Advisory: https://metacpan.org/pod/App::cpanminus
Restart Required: No
Instructions:
1. Update cpanm: 'cpanm App::cpanminus' 2. Verify version: 'cpanm --version' should show 1.7045+ 3. Reinstall any modules installed with vulnerable version.
🔧 Temporary Workarounds
Disable signature verification
allTemporarily disable module signature verification to prevent bypass while planning update.
cpanm --no-verify Module::Name
Use alternative installation method
allInstall Perl modules manually or via system package manager instead of cpanm.
perl Makefile.PL
make
make test
make install
🧯 If You Can't Patch
- Monitor for unexpected module installations or cpanm usage in logs.
- Restrict network access to CPAN mirrors and use internal trusted repositories only.
🔍 How to Verify
Check if Vulnerable:
Run 'cpanm --version' and check if output is exactly '1.7044'.Check Version:
cpanm --versionVerify Fix Applied:
Run 'cpanm --version' and confirm version is 1.7045 or higher.📡 Detection & Monitoring
Log Indicators:
- Unexpected cpanm executions
- Module installations from unusual sources
- Failed signature verification messages
Network Indicators:
- Connections to unofficial CPAN mirrors
- Unencrypted downloads of Perl modules
SIEM Query:
process_name='cpanm' AND command_line LIKE '%--verify%'🔗 References
- https://blog.hackeriet.no/cpan-signature-verification-vulnerabilities/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DENFY4CRTIZL5WYYUYUM4VKCJNXO4QIW/
- https://metacpan.org/pod/App::cpanminus
- https://blog.hackeriet.no/cpan-signature-verification-vulnerabilities/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DENFY4CRTIZL5WYYUYUM4VKCJNXO4QIW/
- https://metacpan.org/pod/App::cpanminus
