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Description
The software 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.
Modes of Introduction:
– Implementation
Likelihood of Exploit: Medium
Related Weaknesses
CWE-681
CWE-681
CWE-681
CWE-124
CWE-120
Consequences
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.
Potential Mitigations
Phase: Requirements
Description:
Choose a language which is not subject to these casting flaws.
Phase: Architecture and Design
Description:
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.
Phase: Implementation
Description:
Error check the return values of all functions. Be aware of implicit casts made, and use unsigned variables for sizes if at all possible.
CVE References
