Predictable Seed in Pseudo-Random Number Generator (PRNG)

A Pseudo-Random Number Generator (PRNG) is initialized from a predictable seed, such as the process ID or system time.


Description

The use of predictable seeds significantly reduces the number of possible seeds that an attacker would need to test in order to predict which random numbers will be generated by the PRNG.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Both of these examples use a statistical PRNG seeded with the current value of the system clock to generate a random number:

Random random = new Random(System.currentTimeMillis());
int accountID = random.nextInt();
srand(time());
int randNum = rand();

An attacker can easily predict the seed used by these PRNGs, and so also predict the stream of random numbers generated. Note these examples also exhibit CWE-338 (Use of Cryptographically Weak PRNG).

See Also

SEI CERT Oracle Secure Coding Standard for Java - Guidelines 49. Miscellaneous (MSC)

Weaknesses in this category are related to the rules and recommendations in the Miscellaneous (MSC) section of the SEI CERT Oracle Secure Coding Standard for Java.

Encrypt Data

Weaknesses in this category are related to the design and architecture of data confidentiality in a system. Frequently these deal with the use of encryption libraries....

SFP Primary Cluster: Predictability

This category identifies Software Fault Patterns (SFPs) within the Predictability cluster.

Comprehensive CWE Dictionary

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Entries with Maintenance Notes

CWE entries in this view have maintenance notes. Maintenance notes are an indicator that an entry might change significantly in future versions. This view was created...

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...


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