CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)

Code Examples & CVEs

Demonstrative Examples

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

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).

BadJava

Random random = new Random(System.currentTimeMillis());int accountID = random.nextInt();

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

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).

BadC

srand(time());int randNum = rand();

Observed CVE Examples (5)

CVE-2020-7010

Cloud application on Kubernetes generates passwords using a weak random number generator based on deployment time.

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CVE-2019-11495

server uses erlang:now() to seed the PRNG, which results in a small search space for potential random seeds

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CVE-2008-0166

The removal of a couple lines of code caused Debian's OpenSSL Package to only use the current process ID for seeding a PRNG

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CVE-2016-10180

Router's PIN generation is based on rand(time(0)) seeding.

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CVE-2018-9057

cloud provider product uses a non-cryptographically secure PRNG and seeds it with the current time

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-337 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-337, Predictable Seed in Pseudo-Random Number Generator (PRNG), throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Apply Libraries or Frameworks controls for Predictable Seed in Pseudo-Random Number Generator (PRNG)

MITRE associates mitigation with Architecture and Design, Requirements, and Implementation; the listed strategies include Libraries or Frameworks; documented detection approaches include Automated Static Analysis. Use these source-defined anchors to turn CWE-337 into implementation, review, and verification checks for the affected component.

CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG) — MITRE CWE

Triage CWE-337 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-337, Predictable Seed in Pseudo-Random Number Generator (PRNG), has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-337

Apply MITRE's full root-cause mapping guidance when using CWE-337, Predictable Seed in Pseudo-Random Number Generator (PRNG). Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-337 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-337, Predictable Seed in Pseudo-Random Number Generator (PRNG). Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)?+

CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG) is a Common Weakness Enumeration (CWE) entry maintained by MITRE. A Pseudo-Random Number Generator (PRNG) is initialized from a predictable seed, such as the process ID or system time. 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.

What are the security consequences of Predictable Seed in Pseudo-Random Number Generator (PRNG)?+

If exploited, CWE-337 (Predictable Seed in Pseudo-Random Number Generator (PRNG)) it can compromise Other, leading to outcomes such as Varies by Context.

How do you prevent or mitigate Predictable Seed in Pseudo-Random Number Generator (PRNG)?+

Recommended mitigations for CWE-337 include: Use non-predictable inputs for seed generation.

Which programming languages are affected by Predictable Seed in Pseudo-Random Number Generator (PRNG)?+

CWE-337 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Predictable Seed in Pseudo-Random Number Generator (PRNG)?+

MITRE documents real CVEs mapped to CWE-337, including CVE-2020-7010, CVE-2019-11495, CVE-2008-0166, CVE-2016-10180 and CVE-2018-9057. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-337 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-337: Predictable Seed in Pseudo-Random Number Generator (PRNG)

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

Phase

Description

Detection Methods

Code Examples & CVEs

Demonstrative Examples

Observed CVE Examples (5)

CWE Relationships

Parent Weaknesses

Source-backed guidance

Verify controls for CWE-337 with SSDF evidence

Apply Libraries or Frameworks controls for Predictable Seed in Pseudo-Random Number Generator (PRNG)

Triage CWE-337 against known exploitation evidence

Apply precise root-cause mapping to CWE-337

Validate CWE-337 with root-cause mapping checks

Frequently Asked Questions

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