Predictable OAuth2 State Parameter Enables Session Hijacking

Mojolicious::Plugin::Web::Auth::OAuth2 versions through 0.17 contain a critical cryptographic weakness in their default state parameter generation. When developers fail to specify a custom state generator, the module falls back to SHA-1 hashing of low-entropy, predictable sources: the epoch timestamp (which attackers can extract from HTTP Date headers) and Perl's rand() function. This breaks the fundamental security contract of OAuth2's state parameter, which exists to prevent cross-site request forgery (CSRF) attacks during the authorization flow. An attacker can now forge valid state parameters, allowing them to intercept legitimate users' OAuth2 callbacks and hijack their authenticated sessions. Any web application using this Perl module with default configuration—particularly those handling sensitive operations like financial transactions or identity management—faces immediate risk of account takeover.

While no specific MITRE ATT&CK techniques are mapped to this CVE, Casky's extended reasoning capabilities would detect the underlying attack patterns associated with CWE-338 (use of cryptographically weak pseudo-random number generator) and CWE-340 (generation of predictable numbers/identifiers). Practitioners using Casky would observe findings flagged for insecure random number generation in authentication flows, weak entropy sources in security-critical parameters, and patterns consistent with CSRF exploitation chains. The platform's skill mapping would highlight the gap between expected OAuth2 security controls and the actual implementation, allowing security teams to identify vulnerable code patterns in dependency audits and code reviews before attackers can abuse them.