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

Opis

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.

Skutki

• Access Control

  Bypass Protection Mechanism

  If a PRNG is used for authentication and authorization, such as a session ID or a seed for generating a cryptographic key, then an attacker may be able to easily guess the ID or cryptographic key and gain access to restricted functionality.

Zapobieganie

• 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.

Przykłady podatności

• 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.

Słabość nadrzędna

• CWE-330 Use of Insufficiently Random Values

Kiedy powstaje

• Architecture and Design
• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Dotyczy

Not Language-Specific, Not Technology-Specific

Uwagi

As of CWE 4.5, terminology related to randomness, entropy, and predictability can vary widely. Within the developer and other communities, "randomness" is used heavily. However, within cryptography, "entropy" is distinct, typically implied as a measurement. There are no commonly-used definitions, even within standards documents and cryptography papers. Future versions of CWE will attempt to define these terms and, if necessary, distinguish between them in ways that are appropriate for different communities but do not reduce the usability of CWE for mapping, understanding, or other scenarios.

Źródła

1. The CLASP Application Security Process — Secure Software, Inc., 2005
2. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 20: Weak Random Numbers." Page 299, McGraw-Hill, 2010