CWE-187: Partial String Comparison

Code Examples & CVEs

Demonstrative Examples

This example defines a fixed username and password. The AuthenticateUser() function is intended to accept a username and a password from an untrusted user, and check to ensure that it matches the username and password. If the username and password match, AuthenticateUser() is intended to indicate that authentication succeeded.

In AuthenticateUser(), the strncmp() call uses the string length of an attacker-provided inPass parameter in order to determine how many characters to check in the password. So, if the attacker only provides a password of length 1, the check will only examine the first byte of the application's password before determining success.

BadC

/* Ignore CWE-259 (hard-coded password) and CWE-309 (use of password system for authentication) for this example. */                                            char *username = "admin";char *pass = "password";                      int AuthenticateUser(char *inUser, char *inPass) {if (strncmp(username, inUser, strlen(inUser))) {logEvent("Auth failure of username using strlen of inUser");return(AUTH_FAIL);}if (! strncmp(pass, inPass, strlen(inPass))) {logEvent("Auth success of password using strlen of inUser");return(AUTH_SUCCESS);}else {logEvent("Auth fail of password using sizeof");return(AUTH_FAIL);}}                      int main (int argc, char **argv) {                         int authResult;                            if (argc < 3) {ExitError("Usage: Provide a username and password");}authResult = AuthenticateUser(argv[1], argv[2]);if (authResult == AUTH_SUCCESS) {DoAuthenticatedTask(argv[1]);}else {ExitError("Authentication failed");}                      }

Observed CVE Examples (5)

CVE-2014-6394

Product does not prevent access to restricted directories due to partial string comparison with a public directory

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CVE-2004-1012

Argument parser of an IMAP server treats a partial command "body[p" as if it is "body.peek", leading to index error and out-of-bounds corruption.

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CVE-2004-0765

Web browser only checks the hostname portion of a certificate when the hostname portion of the URI is not a fully qualified domain name (FQDN), which allows remote attackers to spoof trusted certificates.

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CVE-2002-1374

One-character password by attacker checks only against first character of real password.

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CVE-2000-0979

One-character password by attacker checks only against first character of real password.

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-187 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-187, Partial String Comparison, 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 Partial String Comparison during Testing

MITRE associates mitigation with Testing; recorded impacts include Alter Execution Logic, and Bypass Protection Mechanism; observed examples include CVE-2014-6394, CVE-2004-1012, and CVE-2004-0765. Use these source-defined anchors to turn CWE-187 into implementation, review, and verification checks for the affected component.

CWE-187: Partial String Comparison — MITRE CWE

Triage CWE-187 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-187, Partial String Comparison, 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-187

Apply MITRE's full root-cause mapping guidance when using CWE-187, Partial String Comparison. 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-187 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-187, Partial String Comparison. 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-187: Partial String Comparison?+

CWE-187: Partial String Comparison is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring, leading to resultant weaknesses. For example, an attacker might succeed in authentication by providing a small password that matches the associated portion of the larger, correct password.

What are the security consequences of Partial String Comparison?+

If exploited, CWE-187 (Partial String Comparison) it can compromise Integrity and Access Control, leading to outcomes such as Alter Execution Logic and Bypass Protection Mechanism.

How do you prevent or mitigate Partial String Comparison?+

Recommended mitigations for CWE-187 include: Thoroughly test the comparison scheme before deploying code into production. Perform positive testing as well as negative testing.

Which programming languages are affected by Partial String Comparison?+

CWE-187 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 Partial String Comparison?+

MITRE documents real CVEs mapped to CWE-187, including CVE-2014-6394, CVE-2004-1012, CVE-2004-0765, CVE-2002-1374 and CVE-2000-0979. 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-187 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-187: Partial String Comparison

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-187 with SSDF evidence

Address Partial String Comparison during Testing

Triage CWE-187 against known exploitation evidence

Apply precise root-cause mapping to CWE-187

Validate CWE-187 with root-cause mapping checks

Frequently Asked Questions

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