CWE-339: Small Seed Space in PRNG
A Pseudo-Random Number Generator (PRNG) uses a relatively small seed space, which makes it more susceptible to brute force attacks.
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Overview
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.
Common consequences
What can happen when CWE-339 is exploited.
Varies by Context
Affects: Other
How it happens
When it is introduced
Typically introduced during these phases of the software lifecycle.
How to prevent it
Practical mitigations for CWE-339, grouped by where in the lifecycle they apply.
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.