How severe is CVE-2025-40926?

CVE-2025-40926 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2025-40926 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-40926?

CVE-2025-40926 affects Kazeburo Plack. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-40926?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-40926 have an EU (EUVD) identifier?

Yes. CVE-2025-40926 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-208296.

When was CVE-2025-40926 published?

CVE-2025-40926 was published on 2026-03-05 and last updated on 2026-06-17.

CVE-2025-40926

CVE-2025-40926 is a critical-severity vulnerability in Kazeburo Plack with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-338.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-208296
Weakness: CWE-338
Affected product: Kazeburo Plack
Published: 2026-03-05
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2025-40926?: CVE-2025-40926 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2025-40926 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-40926?: CVE-2025-40926 affects Kazeburo Plack. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-40926?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-40926 have an EU (EUVD) identifier?: Yes. CVE-2025-40926 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-208296.
When was CVE-2025-40926 published?: CVE-2025-40926 was published on 2026-03-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:kazeburo:plack\:\:middleware\:\:session\:\:simple:*:*:*:*:*:perl:*:*

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