CWE-341: Predictable from Observable State

Description

A number or object is predictable based on observations that the attacker can make about the state of the system or network, such as time, process ID, etc.

Potential Impact

Other

Varies by Context

Demonstrative Examples

This code generates a unique random identifier for a user's session.

Bad

function generateSessionID($userID){srand($userID);return rand();}

Because the seed for the PRNG is always the user's ID, the session ID will always be the same. An attacker could thus predict any user's session ID and potentially hijack the session.

This example also exhibits a Small Seed Space (CWE-339).

Mitigations & Prevention

Implementation

Increase the entropy used to seed a PRNG.

Architecture and DesignRequirements

Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").

Implementation

Use a PRNG that periodically re-seeds itself using input from high-quality sources, such as hardware devices with high entropy. However, do not re-seed too frequently, or else the entropy source might block.

Detection Methods

Automated Static Analysis — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

CVE ID	Description
CVE-2024-48445	Chain: e-commerce app relies on an easily-guessable timestamp (CWE-341) in a weak authentication algorithm (CWE-1390)
CVE-2002-0389	Mail server stores private mail messages with predictable filenames in a world-executable directory, which allows local users to read private mailing list archives.
CVE-2001-1141	PRNG allows attackers to use the output of small PRNG requests to determine the internal state information, which could be used by attackers to predict future pseudo-random numbers.
CVE-2000-0335	DNS resolver library uses predictable IDs, which allows a local attacker to spoof DNS query results.
CVE-2005-1636	MFV. predictable filename and insecure permissions allows file modification to execute SQL queries.

Taxonomy Mappings

PLOVER: — Predictable from Observable State

Frequently Asked Questions

What is CWE-341?

CWE-341 (Predictable from Observable State) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. A number or object is predictable based on observations that the attacker can make about the state of the system or network, such as time, process ID, etc.

How can CWE-341 be exploited?

Attackers can exploit CWE-341 (Predictable from Observable State) to varies by context. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.

How do I prevent CWE-341?

Key mitigations include: Increase the entropy used to seed a PRNG.

What is the severity of CWE-341?

CWE-341 is classified as a Base-level weakness (Medium abstraction). It has been observed in 5 real-world CVEs.