Insecure Randomness When Using a SecureRandom Instance Constructed by Spring Security

Vulnerability

Description

CVE-2019-3795 is an insecure randomness vulnerability in Spring Security affecting versions 4.2.x before 4.2.12, 5.0.x before 5.0.12, and 5.1.x before 5.1.5. The issue lies in the SecureRandomFactoryBean#setSeed method, which allows an application to provide a seed for configuring a SecureRandom instance. When a seed is supplied, the resulting random values may be predictable if an attacker is able to observe those values.

Attack

Vector and Prerequisites

Exploitation requires two conditions: the application must explicitly call setSeed with a seed, and the attacker must be able to inspect the random output generated from that seeded instance. This is not a remote code execution or network-based attack; rather, it weakens the security of any cryptographic operations relying on the seeded SecureRandom. Typical scenarios include session token generation or CSRF tokens where randomness is critical.

Impact

If an attacker can observe enough random outputs, they may be able to reconstruct the internal state and predict future random values. This could lead to session hijacking, token forgery, or bypassing security controls that depend on unpredictability. The vulnerability is rated moderate severity, as it requires specific conditions to be exploitable.

Mitigation

Users should upgrade to patched versions: 4.2.12, 5.0.12, or 5.1.5. Alternatively, avoid using SecureRandomFactoryBean#setSeed and rely on the default seeded instance. The GitHub advisory [2] and NVD entry [1] provide more details.