VariantDraftCWE-332

CWE-332: Insufficient Entropy in PRNG

Description

The lack of entropy available for, or used by, a Pseudo-Random Number Generator (PRNG) can be a stability and security threat.

Abstraction: VariantA weakness tied to a specific language, technology or resource.
Likelihood of exploit: Medium
Status: Draft

Common consequences

Availability
DoS: Crash, Exit, or Restart
If a pseudo-random number generator is using a limited entropy source which runs out (if the generator fails closed), the program may pause or crash.
Access ControlOther
Bypass Protection Mechanism; Other
If a PRNG is using a limited entropy source which runs out, and the generator fails open, the generator could produce predictable random numbers. Potentially a weak source of random numbers could weaken the encryption method used for authentication of users.

Potential mitigations

Architecture and DesignRequirementsLibraries or Frameworks
Use products or modules that conform to FIPS 140-2 to avoid obvious entropy problems. Consult FIPS 140-2 Annex C (Approved Random Number Generators).
Implementation
Consider a PRNG that re-seeds itself as needed from high-quality pseudo-random output, such as hardware devices.
Architecture and Design
When deciding which PRNG to use, look at its sources of entropy. Depending on what your security needs are, you may need to use a random number generator that always uses strong random data -- i.e., a random number generator that attempts to be strong but will fail in a weak way or will always provide some middle ground of protection through techniques like re-seeding. Generally, something that always provides a predictable amount of strength is preferable.

Related weaknesses

Parent weaknesses

CWE-331Insufficient Entropy

CAPEC attack patterns that exploit it

CWE 4.20 links no CAPEC attack pattern to this weakness.

Common consequences

Availability

DoS: Crash, Exit, or Restart

If a pseudo-random number generator is using a limited entropy source which runs out (if the generator fails closed), the program may pause or crash.

Access ControlOther

Bypass Protection Mechanism; Other

If a PRNG is using a limited entropy source which runs out, and the generator fails open, the generator could produce predictable random numbers. Potentially a weak source of random numbers could weaken the encryption method used for authentication of users.

Potential mitigations

Architecture and DesignRequirementsLibraries or Frameworks

Use products or modules that conform to FIPS 140-2 to avoid obvious entropy problems. Consult FIPS 140-2 Annex C (Approved Random Number Generators).

Implementation

Consider a PRNG that re-seeds itself as needed from high-quality pseudo-random output, such as hardware devices.

Architecture and Design

When deciding which PRNG to use, look at its sources of entropy. Depending on what your security needs are, you may need to use a random number generator that always uses strong random data -- i.e., a random number generator that attempts to be strong but will fail in a weak way or will always provide some middle ground of protection through techniques like re-seeding. Generally, something that always provides a predictable amount of strength is preferable.