CWE-1241: Use of Predictable Algorithm in Random Number Generator

Extended Description

Pseudo-random number generator algorithms are predictable because their registers have a finite number of possible states, which eventually lead to repeating patterns. As a result, pseudo-random number generators (PRNGs) can compromise their randomness or expose their internal state to various attacks, such as reverse engineering or tampering.

Code Examples & CVEs

Demonstrative Examples

The example code is taken from the PRNG inside the buggy OpenPiton SoC of HACK@DAC'21 [REF-1370]. The SoC implements a pseudo-random number generator using a Linear Feedback Shift Register (LFSR).

BadVerilog

reg in_sr, entropy16_valid; 						reg [15:0] entropy16; 						 						assign entropy16_o = entropy16; 						assign entropy16_valid_o = entropy16_valid; 						 						always @ (*) 						begin 						 							in_sr = ^ (poly_i [15:0] & entropy16 [15:0]); 						 						end

Observed CVE Examples (1)

CVE-2021-3692

PHP framework uses mt_rand() function (Marsenne Twister) when generating tokens

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-1241 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-1241, Use of Predictable Algorithm in Random Number Generator, 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

Address Use of Predictable Algorithm in Random Number Generator during Architecture and Design

MITRE associates mitigation with Architecture and Design, and Implementation; recorded impacts include Read Application Data; the entry maps to CAPEC-97. Use these source-defined anchors to turn CWE-1241 into implementation, review, and verification checks for the affected component.

CWE-1241: Use of Predictable Algorithm in Random Number Generator — MITRE CWE

Triage CWE-1241 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-1241, Use of Predictable Algorithm in Random Number Generator, 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-1241

Apply MITRE's full root-cause mapping guidance when using CWE-1241, Use of Predictable Algorithm in Random Number Generator. 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-1241 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-1241, Use of Predictable Algorithm in Random Number Generator. 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-1241: Use of Predictable Algorithm in Random Number Generator?+

CWE-1241: Use of Predictable Algorithm in Random Number Generator is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The device uses an algorithm that is predictable and generates a pseudo-random number. Pseudo-random number generator algorithms are predictable because their registers have a finite number of possible states, which eventually lead to repeating patterns. As a result, pseudo-random number generators (PRNGs) can compromise their randomness or expose their internal state to various attacks, such as reverse engineering or tampering.

What are the security consequences of Use of Predictable Algorithm in Random Number Generator?+

If exploited, CWE-1241 (Use of Predictable Algorithm in Random Number Generator) it can compromise Confidentiality, leading to outcomes such as Read Application Data.

How do you prevent or mitigate Use of Predictable Algorithm in Random Number Generator?+

Recommended mitigations for CWE-1241 include: It is highly recommended to use a true random number generator (TRNG) to ensure the security of encryption schemes. Hardware-based TRNGs generate unpredictable, unbiased, and independent random numbers because they employ physical phenomena, e.g., electrical noise, as sources to generate random numbers. It is highly recommended to use a true random number generator (TRNG) to ensure the security of encryption schemes. Hardware-based TRNGs generate unpredictable, unbiased, and independent random numbers because they employ physical phenomena, e.g., electrical noise, as sources to generate random numbers.

What are real-world examples of Use of Predictable Algorithm in Random Number Generator?+

MITRE documents real CVEs mapped to CWE-1241, including CVE-2021-3692. 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-1241 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-1241: Use of Predictable Algorithm in Random Number Generator

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