CWE-196: Unsigned to Signed Conversion Error

VariantDraftExploit Likelihood: Medium

The product uses an unsigned primitive and performs a cast to a signed primitive, which can produce an unexpected value if the value of the unsigned primitive can not be represented using a signed primitive.

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Extended Description

Although less frequent an issue than signed-to-unsigned conversion, unsigned-to-signed conversion can be the perfect precursor to dangerous buffer underwrite conditions that allow attackers to move down the stack where they otherwise might not have access in a normal buffer overflow condition. Buffer underwrites occur frequently when large unsigned values are cast to signed values, and then used as indexes into a buffer or for pointer arithmetic.

Technical Details

Structure
Simple
Vulnerability Mapping
ALLOWED

Applicable To

Languages
CC++
Platforms

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-196 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-196, Unsigned to Signed Conversion Error, 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 Unsigned to Signed Conversion Error during Requirements

MITRE associates mitigation with Requirements, Architecture and Design, and Implementation; documented detection approaches include Automated Static Analysis; recorded impacts include DoS: Crash, Exit, or Restart, Modify Memory, Execute Unauthorized Code or Commands, and Bypass Protection Mechanism. Use these source-defined anchors to turn CWE-196 into implementation, review, and verification checks for the affected component.

CWE-196: Unsigned to Signed Conversion Error — MITRE CWE

Triage CWE-196 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-196, Unsigned to Signed Conversion Error, 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-196

Apply MITRE's full root-cause mapping guidance when using CWE-196, Unsigned to Signed Conversion Error. 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-196 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-196, Unsigned to Signed Conversion Error. 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-196: Unsigned to Signed Conversion Error?+

CWE-196: Unsigned to Signed Conversion Error is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product uses an unsigned primitive and performs a cast to a signed primitive, which can produce an unexpected value if the value of the unsigned primitive can not be represented using a signed primitive. Although less frequent an issue than signed-to-unsigned conversion, unsigned-to-signed conversion can be the perfect precursor to dangerous buffer underwrite conditions that allow attackers to move down the stack where they otherwise might not have access in a normal buffer overflow condition. Buffer underwrites occur frequently when large unsigned values are cast to signed values, and then used as indexes into a buffer or for pointer arithmetic.

What are the security consequences of Unsigned to Signed Conversion Error?+

If exploited, CWE-196 (Unsigned to Signed Conversion Error) it can compromise Availability, Integrity, Confidentiality and Access Control, leading to outcomes such as DoS: Crash, Exit, or Restart, Modify Memory, Execute Unauthorized Code or Commands and Bypass Protection Mechanism.

How do you prevent or mitigate Unsigned to Signed Conversion Error?+

Recommended mitigations for CWE-196 include: Choose a language which is not subject to these casting flaws. Design object accessor functions to implicitly check values for valid sizes. Ensure that all functions which will be used as a size are checked previous to use as a size. If the language permits, throw exceptions rather than using in-band errors. Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.

Which programming languages are affected by Unsigned to Signed Conversion Error?+

CWE-196 commonly affects C and C++. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-196 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.

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