CVE-2025-40926: Kazeburo Plack::middleware::session::simple vulnerability (CVSS 9.8)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Kazeburo Plack::middleware::session::simple< 0.05

Remediation

Fixed in

Kazeburo Plack::middleware::session::simple≥ 0.05

Patch & vendor advisories

References

https://github.com/kazeburo/Plack-Middleware-Session-Simple/commit/760bb358b8f53e52cf415888a4ac858fd99bb24e.patchPatch
https://github.com/kazeburo/Plack-Middleware-Session-Simple/pull/4Issue TrackingPatch
https://metacpan.org/release/KAZEBURO/Plack-Middleware-Session-Simple-0.04/source/lib/Plack/Middleware/Session/Simple.pm#L43Issue TrackingProduct
https://metacpan.org/release/KAZEBURO/Plack-Middleware-Session-Simple-0.05/changes
https://security.metacpan.org/docs/guides/random-data-for-security.htmlThird Party Advisory
https://www.cve.org/CVERecord?id=CVE-2025-40923Third Party Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2025-40926 being actively exploited?

CVE-2025-40926 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.45%.

How severe is CVE-2025-40926?

CVE-2025-40926 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.45% probability of exploitation.

Which products are affected by CVE-2025-40926?

Affected products include Kazeburo Plack::middleware::session::simple.

How do I fix CVE-2025-40926?

Upgrade affected software to a fixed version, for example Kazeburo Plack::middleware::session::simple 0.05 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-40926 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation works Book a demo