CWE-134: Use of Externally-Controlled Format String
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How it's found
Use of Externally-Controlled Format String is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
Consequences
- Read Memory: Format string problems allow for information disclosure which can severely simplify exploitation of the program.
- Modify Memory, Execute Unauthorized Code or Commands: Format string problems can result in the execution of arbitrary code, buffer overflows, denial of service, or incorrect data representation.
Mitigations
- Requirements: Choose a language that is not subject to this flaw.
- Implementation: Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings. [REF-116] [REF-117]
- Build and Compilation: Run compilers and linkers with high warning levels, since they may detect incorrect usage.
Where this fits in a TurboPentest engagement
TurboPentest's agentic pentest is powerful and covers a broad range of issues automatically. This particular class is best confirmed in a manual IntegSec engagement, where human pentesters apply deeper methodology and a larger context window than any automated pass.
Frequently asked questions
What is CWE-134?
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How do you find Use of Externally-Controlled Format String?
Use of Externally-Controlled Format String is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
What is the impact of CWE-134?
Read Memory: Format string problems allow for information disclosure which can severely simplify exploitation of the program. Modify Memory, Execute Unauthorized Code or Commands: Format string problems can result in the execution of arbitrary code, buffer overflows, denial of service, or incorrect data representation.
Does TurboPentest test for Use of Externally-Controlled Format String?
TurboPentest's agentic pentest is powerful and covers a broad range of issues automatically. This particular class is best confirmed in a manual IntegSec engagement, where human pentesters apply deeper methodology and a larger context window than any automated pass.
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