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. 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.

CVSS v3 9.1 CRITICAL

9.1^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
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

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-22 14:16

Updated : 2026-08-26 16:51

NVD link : CVE-2026-75870

Mitre link : CVE-2026-75870

CVE.ORG link : CVE-2026-75870

JSON object : View

Products Affected

No product.

CWE

CWE-1394

Use of Default Cryptographic Key

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