# CVE-2026-75870

## Summary

- **CVE ID:** CVE-2026-75870
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)
- **CWE:** CWE-1394
- **Published:** Aug 22, 2026
- **Last Modified:** Aug 25, 2026

## 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.

## Affected Products

- Unknown product (0)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.49%
- **EPSS Percentile:** 40.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-12._