CVE-2026-75870
CVE-2026-75870 is a security vulnerability that is still awaiting full analysis and scoring. The underlying weakness is classified as CWE-1394.
Key facts
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-1394
- Published:
- Last modified:
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.
Frequently asked questions
- What is 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.
- Is CVE-2026-75870 being actively exploited?
- It is not currently listed in CISA's Known Exploited Vulnerabilities catalog, and no EPSS exploit-prediction score is available yet.
- How do I fix CVE-2026-75870?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- When was CVE-2026-75870 published?
- CVE-2026-75870 was published on 2026-08-22.
References
- 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
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