Weakness · High
CWE-196: Unsigned to Signed Conversion Error
What it is
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.
- Severity (our rating)
- High
- Likelihood of exploit
- Medium
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
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 an attacker can do
- DoS: Crash, Exit, or Restart (Availability)
- Modify Memory (Integrity)
- Execute Unauthorized Code or Commands (Integrity, Confidentiality, Availability, Access Control)
- Bypass Protection Mechanism (Integrity, Confidentiality, Availability, Access Control)
How to prevent it
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.
How to find it
- 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.)
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.