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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-75870
StatePUBLISHED
AssignerCPANSec
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-22 14:16:33 UTC
Updated2026-08-22 19:16:20 UTC
DescriptionPunk 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.

Risk And Classification

Problem Types: CWE-1394 | CWE-1394 CWE-1394 Use of Default Cryptographic Key

References

ReferenceSourceLinkTags
metacpan.org/release/LNATION/Punk-0.17/source/include/punk/punk_session.h 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
metacpan.org/release/LNATION/Punk-0.18/source/Changes 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
www.openwall.com/lists/oss-security/2026/08/22/5 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com
metacpan.org/release/LNATION/Punk-0.17/view/lib/Punk.pm 9b29abf9-4ab0-4765-b253-1875cd9b441e metacpan.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

Solutions

CNA: Upgrade to Punk 0.18 or later.

Workarounds

CNA: For deployments that cannot upgrade to 0.18, declare the session keyword with a non-empty secret. The secret keyword fails closed, so sourcing the key through it turns a missing configuration path or an unset environment variable into a startup error.

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