What’s Vulnerable › Vulnerabilities

CVE-2026-75870: Punk versions before 0.18 for Perl allow session cookie forgery via an empty default HMAC key when a session is declared without a secret

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-22 · updated 2026-10-14
• Weakness: CWE-1394

Description

Punk versions before 0.18 for Perl allow session cookie forgery via an empty default HMAC key when a session is declared without a secret. The session keyword freezes its options onto the application as given: it does not require a secret, warn, or refuse to start when one is absent. The cookie read and the write-back both default that key to the empty string, so a declaration with no secret option, or with an undefined or empty one, signs and verifies with a zero-length HMAC-SHA256 key. An attacker who knows the cookie format can then mint one offline carrying any contents the session holds, such as a user identifier or a role. Nothing marks the misconfiguration at runtime: cookies are well formed and sessions round-trip as expected.

References

• https://metacpan.org/release/LNATION/Punk-0.17/source/include/punk/punk_session.h
• https://metacpan.org/release/LNATION/Punk-0.17/view/lib/Punk.pm
• https://metacpan.org/release/LNATION/Punk-0.18/source/Changes
• http://www.openwall.com/lists/oss-security/2026/08/22/5

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