CVE-2026-3255 identifies a cryptographic weakness in the HTTP::Session2 Perl module used for session management. The vulnerability arises because the session ID generator relies on the built-in rand() function, which is not cryptographically secure, combined with predictable inputs such as the epoch timestamp and process ID (PID). Since the PID is drawn from a small range and the epoch time can be guessed or inferred from HTTP headers, the resulting SHA-1 hash used as the session ID is predictable. This predictability allows attackers to guess or brute force valid session IDs, enabling session hijacking or impersonation attacks. Although HTTP::Session2 versions after 1.02 attempt to use the /dev/urandom device for generating session IDs, if this device is unavailable (notably on Windows platforms), the module falls back to the insecure method. This fallback behavior introduces a significant security risk in environments without access to a secure entropy source. The vulnerability is categorized under CWE-340 (Generation of Predictable Numbers or Identifiers) and CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator). No CVSS score is assigned yet, and no known exploits have been reported in the wild. However, the weakness fundamentally undermines session security in affected versions, potentially exposing web applications to session fixation and hijacking attacks.

The primary impact of CVE-2026-3255 is the compromise of session confidentiality and integrity. Predictable session IDs allow attackers to impersonate legitimate users by guessing or brute forcing valid session tokens, leading to unauthorized access to user accounts and sensitive data. This can result in data breaches, privilege escalation, and unauthorized transactions. The vulnerability affects any web application using vulnerable versions of HTTP::Session2, especially those deployed on Windows or other systems lacking /dev/urandom. The ease of exploitation is high because no authentication or user interaction is required to attempt session ID prediction. The scope includes all affected versions of HTTP::Session2, which may be embedded in various Perl-based web applications worldwide. Organizations relying on this module for session management face increased risk of session hijacking attacks, potentially undermining user trust and regulatory compliance. Although no exploits are currently known, the vulnerability represents a significant risk if attackers develop automated tools to predict session IDs.

1. Upgrade HTTP::Session2 to the latest version that ensures the use of cryptographically secure random number generators without fallback to insecure methods. 2. Verify that the deployment environment provides access to a secure entropy source such as /dev/urandom or an equivalent cryptographically secure random device. 3. On Windows systems, consider configuring or installing libraries that provide secure randomness or migrate to platforms where secure entropy sources are available. 4. Audit all web applications using HTTP::Session2 to confirm session ID generation does not rely on predictable inputs or weak PRNGs. 5. Implement additional session security controls such as short session lifetimes, IP address binding, and multi-factor authentication to reduce the impact of potential session hijacking. 6. Monitor logs for unusual session activity or repeated session ID guessing attempts. 7. Educate developers and system administrators about the risks of using non-cryptographic random functions for security tokens. 8. Consider using alternative session management libraries that have been independently audited for cryptographic security.