Weakness · Medium
CWE-339: Small Seed Space in PRNG
What it is
A Pseudo-Random Number Generator (PRNG) uses a relatively small seed space, which makes it more susceptible to brute force attacks.
- Severity (our rating)
- Medium
- 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 entirely deterministic once seeded, so it should be extremely difficult to guess the seed. If an attacker can collect the outputs of a PRNG and then brute force the seed by trying every possibility to see which seed matches the observed output, then the attacker will know the output of any subsequent calls to the PRNG. A small seed space implies that the attacker will have far fewer possible values to try to exhaust all possibilities.
What an attacker can do
- Varies by Context (Other)
How to prevent it
Architecture and Design
- Use well vetted pseudo-random number generating algorithms with adequate length seeds. Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a "random enough" number.
- Use products or modules that conform to FIPS 140-2 to avoid obvious entropy problems, or use the more recent FIPS 140-3 if possible.
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.