Vulnerability in Kazeburo Plack\
CVE-2025-40926
Plack::Middleware::Session::Simple versions before 0.05 for Perl generates session ids insecurely. The default session id generator returns a SHA-1 hash seeded with the built-in rand function, the epoch time, and the PID. The PID will come from a small set of numbers, and the epoch time may be guessed, if it is not leaked from the HTTP Date header. The built-in rand function is unsuitable for cryptographic usage. Predictable session ids could allow an attacker to gain access to systems. Plack::Middleware::Session::Simple is intended to be compatible with Plack::Middleware::Session, which had a similar security issue CVE-2025-40923.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.004 (35.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
Weakness classification (CWE)
References
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (Product, Issue Tracking)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (issue-tracking, Patch, Issue Tracking)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (Patch, patch)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (related, vendor-advisory, Third Party Advisory, vdb-entry)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (technical-description, Third Party Advisory)
- 9b29abf9-4ab0-4765-b253-1875cd9b441e (release-notes)
Frequently asked questions
- What is CVE-2025-40926?
- CVE-2025-40926 is a critical-severity vulnerability in Kazeburo Plack\, classified under Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG). CVSS score: 9.8/10. Published 2026-03-05.
- How severe is CVE-2025-40926?
- Critical severity. CVSS v3 base score is 9.8 out of 10.