Plack::Middleware::Session::Simple: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
CVE-2025-40926 is a critical-severity use of cryptographically weak pseudo-random number generator (PRNG) vulnerability in Plack::Middleware::Session::Simple from Kazeburo, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 0.05 as the first without the flaw, so updating Plack::Middleware::Session::Simple to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.5% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Plack::Middleware::Session::Simple to 0.05 or a later version.
- Update Plack to 0.05 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| KAZEBURO | Plack::Middleware::Session::Simple | before 0.05 | 0.05 |
| Kazeburo | Plack | before 0.05 | 0.05 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong.
How developers prevent this class of flaw
- Use functions or hardware which use a hardware-based random number generation for all crypto. This is the recommended solution. Use CyptGenRandom on Windows, or hw_rand() on Linux.
More Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) vulnerabilities (CWE-338)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Third-party and government advisories
- security.metacpan.org/docs/guides/random-data-for-security.htmlThird Party Advisory
- cve.org/CVERecord?id=CVE-2025-40923Third Party Advisory
Other references
Recent Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) vulnerabilities
- 9.1 Critical severity
- 9.1 Critical severity
- 8.2 High severity
- 9.1 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
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