CVE-2026-56016: Weak RNG (CVSS 5.9)

Description

CGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources. The generate_id method builds the session id from a MD5 digest of the process id, the epoch time, and the built-in rand() function. All three are predictable, low-entropy sources: the PID is drawn from a small range, the epoch time can be guessed or read from the HTTP Date header, and Perl's rand() is unsuitable for security purposes because it is predictable and reversible. An attacker who predicts a session id can impersonate the corresponding session and bypass authentication.

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CVSS v3.1 Score

5.9

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0032

Probability of exploitation

0.25%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-338 CWE-338

CWE-340 CWE-340

References

Other References

https://metacpan.org/release/MARKSTOS/CGI-Session-4.49/changes https://metacpan.org/release/MARKSTOS/CGI-Session-4.49/source/lib/CGI/Session/ID/md5.pm http://www.openwall.com/lists/oss-security/2026/07/01/6

Frequently Asked Questions

What is CVE-2026-56016? +

CGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources. The generate_id method builds the session id from a MD5 digest of the process id, the epoch time, and the built-in rand() function. All three are predictable, low-entropy sources: the PID is drawn from a small range, the epoch time can be guessed or read from the HTTP Date header, and Perl's rand() is unsuitable for security purposes because it is predictable and reversible. An attacker who predicts a session id can impersonate the corresponding session and bypass authentication. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-56016? +

CVE-2026-56016 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0032, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-56016? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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