Weakness · High
CWE-335: Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)
What it is
The product uses a Pseudo-Random Number Generator (PRNG) but does not correctly manage seeds.
- Severity (our rating)
- High
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
PRNGs are deterministic and, while their output appears random, they cannot actually create entropy. They rely on cryptographically secure and unique seeds for entropy so proper seeding is critical to the secure operation of the PRNG. Management of seeds could be broken down into two main areas: (1) protecting seeds as cryptographic material (such as a cryptographic key); (2) whenever possible, using a uniquely generated seed from a cryptographically secure source PRNGs require a seed as input to generate a stream of numbers that are functionally indistinguishable from random numbers. While the output is, in many cases, sufficient for cryptographic uses, the output of any PRNG is directly determined by the seed provided as input. If the seed can be ascertained by a third party, the entire output of the PRNG can be made known to them. As such, the seed should be kept secret and should ideally not be able to be guessed. For example, the current time may be a poor seed. Knowing the approximate time the PRNG was seeded greatly reduces the possible key space. Seeds do not necessarily need to be unique, but reusing seeds may open up attacks if the seed is discovered.
What an attacker can do
- Bypass Protection Mechanism (Access Control, Other)
- Other (Access Control, Other)
How to prevent it
MITRE lists no specific mitigation for this weakness. Treat it like its parent weaknesses below: validate input, keep the design simple and review the code where it could appear.
How to find it
- Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.