CWE-1286: Improper Validation of Syntactic Correctness of Input

Extended Description

Often, complex inputs are expected to follow a particular syntax, which is either assumed by the input itself, or declared within metadata such as headers. The syntax could be for data exchange formats, markup languages, or even programming languages. When untrusted input is not properly validated for the expected syntax, attackers could cause parsing failures, trigger unexpected errors, or expose latent vulnerabilities that might not be directly exploitable if the input had conformed to the syntax.

Code Examples & CVEs

Demonstrative Examples

The following code loads and parses an XML file.

The XML file is loaded without validating it against a known XML Schema or DTD.

BadJava

// Read DOM                      try {...DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();factory.setValidating( false );....c_dom = factory.newDocumentBuilder().parse( xmlFile );} catch(Exception ex) {...}

Observed CVE Examples (2)

CVE-2016-4029

Chain: incorrect validation of intended decimal-based IP address format (CWE-1286) enables parsing of octal or hexadecimal formats (CWE-1389), allowing bypass of an SSRF protection mechanism (CWE-918).

View Details

CVE-2007-5893

HTTP request with missing protocol version number leads to crash

View Details

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-1286 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-1286, Improper Validation of Syntactic Correctness of Input, 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 Validation of Syntactic Correctness of Input

MITRE associates mitigation with Implementation; the listed strategies include Input Validation; recorded impacts include Varies by Context. Use these source-defined anchors to turn CWE-1286 into implementation, review, and verification checks for the affected component.

CWE-1286: Improper Validation of Syntactic Correctness of Input — MITRE CWE

Triage CWE-1286 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-1286, Improper Validation of Syntactic Correctness of Input, 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-1286

Apply MITRE's full root-cause mapping guidance when using CWE-1286, Improper Validation of Syntactic Correctness of Input. 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-1286 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-1286, Improper Validation of Syntactic Correctness of Input. 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-1286: Improper Validation of Syntactic Correctness of Input?+

CWE-1286: Improper Validation of Syntactic Correctness of Input is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product receives input that is expected to be well-formed - i.e., to comply with a certain syntax - but it does not validate or incorrectly validates that the input complies with the syntax. Often, complex inputs are expected to follow a particular syntax, which is either assumed by the input itself, or declared within metadata such as headers. The syntax could be for data exchange formats, markup languages, or even programming languages. When untrusted input is not properly validated for the expected syntax, attackers could cause parsing failures, trigger unexpected errors, or expose latent vulnerabilities that might not be directly exploitable if the input had conformed to the syntax.

What are the security consequences of Improper Validation of Syntactic Correctness of Input?+

If exploited, CWE-1286 (Improper Validation of Syntactic Correctness of Input) it can compromise Other, leading to outcomes such as Varies by Context.

Which programming languages are affected by Improper Validation of Syntactic Correctness of Input?+

CWE-1286 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 Validation of Syntactic Correctness of Input?+

MITRE documents real CVEs mapped to CWE-1286, including CVE-2016-4029 and CVE-2007-5893. 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-1286 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-1286: Improper Validation of Syntactic Correctness of Input

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

Detection Methods