CVE-2025-40905: WWW::OAuth Perl Weak Entropy Vulnerability

CVE-2025-40905 Overview

CVE-2025-40905 is an Insecure Random Number Generation vulnerability affecting WWW::OAuth version 1.000 and earlier for Perl. The module uses the rand() function as the default source of entropy for cryptographic functions, which is not cryptographically secure. This weakness can allow attackers to predict OAuth tokens and nonces, potentially leading to authentication bypass or session hijacking in applications relying on this module for OAuth authentication.

Critical Impact

Applications using WWW::OAuth 1.000 or earlier may generate predictable OAuth tokens and nonces, enabling attackers to forge authentication credentials or hijack sessions through predictable random value generation.

Affected Products

• WWW::OAuth version 1.000
• WWW::OAuth versions prior to 1.000
• Perl applications using WWW::OAuth for OAuth authentication

Discovery Timeline

• 2026-02-13 - CVE-2025-40905 published to NVD
• 2026-02-17 - Last updated in NVD database

Technical Details for CVE-2025-40905

Vulnerability Analysis

The vulnerability stems from the use of Perl's built-in rand() function for generating cryptographic values in OAuth protocol operations. The rand() function in Perl is designed for general-purpose pseudo-random number generation and is explicitly documented as unsuitable for cryptographic purposes. When used for generating OAuth nonces, tokens, or other security-critical values, the predictable nature of rand() output can be exploited by attackers who understand the underlying algorithm.

OAuth 1.0a requires nonce values to be unique and unpredictable to prevent replay attacks and ensure the integrity of signed requests. By using a non-cryptographic random number generator, the WWW::OAuth module fundamentally undermines this security requirement.

Root Cause

The root cause is the use of CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG). The rand() function in Perl uses a linear congruential generator or similar algorithm that produces deterministic sequences based on the seed value. If an attacker can determine or guess the seed (often based on process start time or other predictable values), they can reproduce the entire sequence of "random" numbers generated by the application.

The vulnerable code can be found at line 86 of the OAuth.pm module, where rand() is used as the default entropy source for cryptographic operations. According to MetaCPAN Security Guide, cryptographic applications should use /dev/urandom, Crypt::URandom, or similar cryptographically secure random sources.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can potentially:

1. Observe OAuth requests from a target application to analyze nonce patterns
2. Determine or brute-force the PRNG seed based on timing information or observed output
3. Predict future nonces and tokens generated by the application
4. Forge valid OAuth signatures or replay previous requests with predicted values

The attack requires understanding of the application's OAuth implementation and timing, but does not require direct access to the vulnerable system.

Detection Methods for CVE-2025-40905

Indicators of Compromise

• Unexpected OAuth authentication successes from unknown sources
• Multiple requests with identical or sequential nonce values
• OAuth signature validation failures followed by successful forgeries
• Anomalous patterns in OAuth request timing correlating with nonce reuse

Detection Strategies

• Audit Perl applications for usage of WWW::OAuth module versions 1.000 or earlier
• Implement monitoring for OAuth nonce reuse or predictable patterns in authentication logs
• Review application dependencies using CPAN security advisories and vulnerability databases
• Conduct code review to identify any direct usage of rand() in security-sensitive contexts

Monitoring Recommendations

• Enable detailed logging of OAuth authentication events including nonces and timestamps
• Set up alerts for repeated authentication attempts with similar nonce patterns
• Monitor for unusual OAuth token usage patterns that may indicate prediction attacks
• Track and baseline normal OAuth request volumes to detect anomalous activity

How to Mitigate CVE-2025-40905

Immediate Actions Required

• Identify all applications using WWW::OAuth 1.000 or earlier in your environment
• Evaluate the criticality of OAuth authentication in affected applications
• Consider implementing additional authentication layers while awaiting a patched version
• Review OAuth logs for any signs of exploitation or nonce prediction attempts

Patch Information

As of the last update on 2026-02-17, consult the MetaCPAN OAuth Module Source and the OpenWall OSS-Security Mailing List for the latest information on patches and updated module versions. Monitor CPAN for new releases of WWW::OAuth that address this cryptographic weakness.

Workarounds

• Override the default random source in WWW::OAuth with a cryptographically secure alternative such as Crypt::URandom
• Implement application-level nonce tracking to detect and reject reused or predictable values
• Add rate limiting and anomaly detection for OAuth authentication endpoints
• Consider migrating to OAuth 2.0 implementations that use more secure token generation methods

The recommended approach for Perl applications requiring cryptographic randomness is to use modules like Crypt::URandom or read directly from /dev/urandom on Unix-like systems. Refer to the MetaCPAN Security Guide and Perl Documentation: rand Function for guidance on proper random number generation for security purposes.