CWE-196: Unsigned to Signed Conversion Error
Official CWE-196 CWE context with Glexia analysis, remediation guidance, related CVEs, and ATT&CK context.
Glexia's Take
CWE-196: Unsigned to Signed Conversion Error
Unsigned to Signed Conversion Error represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Availability: DoS: Crash, Exit, or Restart: Incorrect sign conversions generally lead to undefined behavior, and therefore crashes.
- Integrity: Modify Memory: If a poor cast lead to a buffer overflow or similar condition, data integrity may be affected.
- Integrity,Confidentiality,Availability,Access Control: Execute Unauthorized Code or Commands,Bypass Protection Mechanism: Improper signed-to-unsigned conversions without proper checking can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.
Developer Pattern
CWE-196 is the kind of defect developers can usually prevent with explicit validation, safer framework defaults, and tests that exercise hostile input or unsafe state transitions.
Confidence
high confidence from CWE-196, 4.20.
Official CWE Definition
CWE-196: Unsigned to Signed Conversion Error
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.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- Missing validation
- Unsafe defaults
- Insufficient authorization or memory-safety invariant
Remediation
- Requirements: Choose a language which is not subject to these casting flaws.
- Architecture and Design: 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.
- Implementation: Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.
Detection
- 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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
Mappings
Related CVEs, CWEs, and ATT&CK context
Related CWEs
- CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- CWE-124: Buffer Underwrite ('Buffer Underflow')
- CWE-681: Incorrect Conversion between Numeric Types
- CWE-681: Incorrect Conversion between Numeric Types
- CWE-681: Incorrect Conversion between Numeric Types
- CWE-197: Numeric Truncation Error
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.