Vulnerability · Published Jul 1, 2026 · Assigned by CPANSec
CVE-2026-56016CGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources
Medium 5.9
In plain English
A medium-severity security flaw in CGI::Session::ID::md5 from MARKSTOS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.24 | perl-cgi-session | 4.49-r0 | ALPINE-CVE-2026-56016 |
| Debian:12 | libcgi-session-perl | no fix listed | DEBIAN-CVE-2026-56016 |
| Debian:13 | libcgi-session-perl | no fix listed | DEBIAN-CVE-2026-56016 |
| Debian:14 | libcgi-session-perl | 4.49-1 | DEBIAN-CVE-2026-56016 |
| Ubuntu:22.04:LTS | libcgi-session-perl | no fix listed | UBUNTU-CVE-2026-56016 |
| Ubuntu:24.04:LTS | libcgi-session-perl | no fix listed | UBUNTU-CVE-2026-56016 |
| Ubuntu:25.10 | libcgi-session-perl | no fix listed | UBUNTU-CVE-2026-56016 |
| Ubuntu:26.04:LTS | libcgi-session-perl | no fix listed | UBUNTU-CVE-2026-56016 |
| Ubuntu:26.10 | libcgi-session-perl | no fix listed | UBUNTU-CVE-2026-56016 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MARKSTOS | CGI::Session::ID::md5 | 0 – before 4.49 |
Weakness: CWE-340, CWE-338 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N