CVE-2026-75870: CWE-1394 Use of Default Cryptographic Key
Description
CVE-2026-75870 affects Punk versions before 0.18 for Perl, where session cookies can be forged due to the use of an empty default HMAC key when no secret is provided. The session mechanism does not enforce or warn about the absence of a secret, resulting in signing and verification with a zero-length HMAC-SHA256 key. This allows an attacker who understands the cookie format to create valid session cookies with arbitrary contents such as user identifiers or roles without detection.
CVSS v3.1
Score 9.1critical
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability arises because the Punk session keyword does not require a secret key and defaults to an empty string for the HMAC key if none is provided. Consequently, session cookies are signed and verified using a zero-length HMAC-SHA256 key, enabling an attacker to forge session cookies offline. The forged cookies appear valid and are accepted by the application, potentially allowing unauthorized access or privilege escalation.
Potential Impact
An attacker can create forged session cookies that the application will accept as valid, potentially impersonating users or escalating privileges. This compromises confidentiality and integrity of session data but does not affect availability. The vulnerability has a CVSS score of 9.1 (critical), indicating a high impact on confidentiality and integrity without requiring privileges or user interaction.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, ensure that a non-empty secret is explicitly configured for sessions to avoid defaulting to an empty HMAC key. Avoid deploying Punk versions before 0.18 without proper secret configuration.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- CPANSec
- Date Reserved
- 2026-08-18T11:59:49.642Z
- State
- PUBLISHED
Threat ID: 6a89a9b5acd9273b491a2938
Added to database: 08/22/2026, 13:52:53 UTC
Last enriched: 09/10/2026, 14:49:25 UTC
Last updated: 10/04/2026, 18:53:18 UTC
Views: 70
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