CWE-135: Incorrect Calculation of Multi-Byte String Length
Official CWE-135 CWE context with Glexia analysis, remediation guidance, related CVEs, and ATT&CK context.
Glexia's Take
CWE-135: Incorrect Calculation of Multi-Byte String Length
Incorrect Calculation of Multi-Byte String Length represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Integrity,Confidentiality,Availability: Execute Unauthorized Code or Commands: This weakness may lead to a buffer overflow. Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. This can often be used to subvert any other security service.
- Availability,Confidentiality: Read Memory,DoS: Crash, Exit, or Restart,DoS: Resource Consumption (CPU),DoS: Resource Consumption (Memory): Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
- Confidentiality: Read Memory: In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
Developer Pattern
CWE-135 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-135, 4.20.
Official CWE Definition
CWE-135: Incorrect Calculation of Multi-Byte String Length
The product does not correctly calculate the length of strings that can contain wide or multi-byte characters.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- The following example would be exploitable if any of the commented incorrect malloc calls were used. The output from the printf() statement would be:
Remediation
- Implementation: Always verify the length of the string unit character.
- Implementation: Use length computing functions (e.g. strlen, wcslen, etc.) appropriately with their equivalent type (e.g.: byte, wchar_t, etc.)
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
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.