CWE WEAKNESSES  /  CWE-338

CWE-338

Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)

What it is

The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong.

When a non-cryptographic PRNG is used in a cryptographic context, it can expose the cryptography to certain types of attacks.Often a pseudo-random number generator (PRNG) is not designed for cryptography. Sometimes a mediocre source of randomness is sufficient or preferable for algorithms that use random numbers. Weak generators generally take less processing power and/or do not use the precious, finite, entropy sources on a system. While such PRNGs might have very useful features, these same features could be used to break the cryptography.

Impact

Mitigations

• [Implementation] Use functions or hardware which use a hardware-based random number generation for all crypto. This is the recommended solution. Use CyptGenRandom on Windows, or hw_rand() on Linux.

Real-world CVE examples

• CVE-2021-3692 — PHP framework uses mt_rand() function (Marsenne Twister) when generating tokens
• CVE-2009-3278 — Crypto product uses rand() library function to generate a recovery key, making it easier to conduct brute force attacks.
• CVE-2009-3238 — Random number generator can repeatedly generate the same value.
• CVE-2009-2367 — Web application generates predictable session IDs, allowing session hijacking.
• CVE-2008-0166 — SSL library uses a weak random number generator that only generates 65,536 unique keys.

Related weaknesses

Source: MITRE CWE. View on cwe.mitre.org →