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.
History

Tue, 25 Aug 2026 20:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Sun, 23 Aug 2026 17:45:00 +0000

Type Values Removed Values Added
First Time appeared Punk
Punk punk
Vendors & Products Punk
Punk punk

Sat, 22 Aug 2026 19:30:00 +0000

Type Values Removed Values Added
References

Sat, 22 Aug 2026 13:45:00 +0000

Type Values Removed Values Added
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.
Title 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
Weaknesses CWE-1394
References

cve-icon MITRE

Status: PUBLISHED

Assigner: CPANSec

Published: 2026-08-22T13:35:58.346Z

Updated: 2026-08-25T19:28:36.443Z

Reserved: 2026-08-18T11:59:49.642Z

Link: CVE-2026-75870

cve-icon Vulnrichment

Updated: 2026-08-22T19:07:10.053Z

cve-icon NVD

Status : Deferred

Published: 2026-08-22T14:16:33.813

Modified: 2026-08-26T16:51:19.490

Link: CVE-2026-75870

cve-icon Redhat

No data.