CVE-2016-1902 in Symfony
Summary
by MITRE
The nextBytes function in the SecureRandom class in Symfony before 2.3.37, 2.6.x before 2.6.13, and 2.7.x before 2.7.9 does not properly generate random numbers when used with PHP 5.x without the paragonie/random_compat library and the openssl_random_pseudo_bytes function fails, which makes it easier for attackers to defeat cryptographic protection mechanisms via unspecified vectors.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-1902 resides within the SecureRandom class implementation in Symfony framework versions prior to specific patches. This flaw specifically affects PHP 5.x environments that lack the paragonie/random_compat library and experience failures with the openssl_random_pseudo_bytes function. The issue manifests in the nextBytes function which is responsible for generating cryptographically secure random numbers essential for cryptographic operations within the framework. When these conditions are met, the random number generation becomes predictable and vulnerable to exploitation by malicious actors seeking to compromise security mechanisms.
The technical root cause of this vulnerability stems from improper fallback mechanisms in the SecureRandom implementation. When the primary cryptographic random number generator fails due to missing dependencies or function failures, the system should gracefully fall back to alternative secure methods or at minimum fail securely. However, in affected Symfony versions, the system fails to maintain cryptographic security guarantees when the preferred random number generation methods are unavailable, resulting in weak or predictable random sequences. This weakness directly violates the fundamental principles of cryptographic security where random number generation must remain unpredictable and uniformly distributed to prevent attackers from deriving sensitive information or bypassing protection mechanisms.
The operational impact of CVE-2016-1902 extends beyond simple random number generation failures as it undermines the integrity of cryptographic protection mechanisms throughout the affected Symfony applications. Attackers can exploit this vulnerability to predict random values used for session management, password reset tokens, CSRF protection, encryption keys, and other security-critical components. The unspecified vectors mentioned in the description suggest that various attack scenarios could exploit this weakness, potentially leading to session hijacking, privilege escalation, data breaches, and other serious security compromises. This vulnerability particularly affects web applications relying on Symfony's cryptographic features without proper fallback mechanisms or additional security libraries.
Security practitioners should immediately apply the available patches to upgrade Symfony to versions 2.3.37, 2.6.13, or 2.7.9 respectively, which contain the necessary fixes for this vulnerability. Additionally, organizations should ensure their PHP environments include the paragonie/random_compat library to provide proper fallback mechanisms for random number generation. The mitigation strategy should also include monitoring applications for proper fallback behavior and implementing additional security controls such as input validation, secure session management, and regular security assessments. This vulnerability aligns with CWE-330 weakness category related to insufficient entropy in random number generation, and represents a technique that could be classified under ATT&CK tactics involving privilege escalation and credential access through cryptographic weakness exploitation.