What are the security consequences of Improper Handling of URL Encoding (Hex Encoding)?

If exploited, CWE-177 (Improper Handling of URL Encoding (Hex Encoding)) it can compromise Integrity, leading to outcomes such as Unexpected State.

Which programming languages are affected by Improper Handling of URL Encoding (Hex Encoding)?

CWE-177 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 Improper Handling of URL Encoding (Hex Encoding)?

MITRE documents real CVEs mapped to CWE-177, including CVE-2000-0900, CVE-2005-2256, CVE-2004-2121, CVE-2004-0280 and CVE-2003-0424. 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-177 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-177: Improper Handling of URL Encoding (Hex Encoding)

Q: What is CWE-177: Improper Handling of URL Encoding (Hex Encoding)?

CWE-177: Improper Handling of URL Encoding (Hex Encoding) is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product does not properly handle when all or part of an input has been URL encoded.

Verify controls for CWE-177 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-177, Improper Handling of URL Encoding (Hex Encoding), 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 Input Validation controls for Improper Handling of URL Encoding (Hex Encoding)

MITRE associates mitigation with Architecture and Design, and Implementation; the listed strategies include Input Validation; recorded impacts include Unexpected State. Use these source-defined anchors to turn CWE-177 into implementation, review, and verification checks for the affected component.

CWE-177: Improper Handling of URL Encoding (Hex Encoding) — MITRE CWE

Triage CWE-177 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-177, Improper Handling of URL Encoding (Hex Encoding), 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-177

Apply MITRE's full root-cause mapping guidance when using CWE-177, Improper Handling of URL Encoding (Hex Encoding). 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-177 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-177, Improper Handling of URL Encoding (Hex Encoding). 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

CWE-177: Improper Handling of URL Encoding (Hex Encoding)

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

Detection Methods

Code Examples & CVEs

Observed CVE Examples (19)

CWE Relationships

Parent Weaknesses

Source-backed guidance

Verify controls for CWE-177 with SSDF evidence

Apply Input Validation controls for Improper Handling of URL Encoding (Hex Encoding)

Triage CWE-177 against known exploitation evidence

Apply precise root-cause mapping to CWE-177

Validate CWE-177 with root-cause mapping checks

Frequently Asked Questions

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