Null-terminated byte strings are, by definition, null-terminated. String operations cannot determine the length or end of strings that are not properly null-terminated, which can consequently result in buffer overflows and other undefined behavior.
Unable to render {include} The included page could not be found.
Unable to render {include} The included page could not be found.
Unable to render {include} The included page could not be found.
Unable to render {include} The included page could not be found.
Exception
An exception to this rule applies if the intent of the programmer is to convert a null-terminated byte string to a character array. To be compliant with this standard, this intent must be clearly stated in comments.
Risk Assessment
Failure to properly null terminate null-terminated byte strings can result in buffer overflows and the execution of arbitrary code with the permissions of the vulnerable process by an attacker.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
STR32-C |
3 (high) |
2 (probable) |
2 (medium) |
P12 |
L1 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Mitigation Strategies
(Section under construction by Ciera. Just wanted to get some current notes down here before I clean it up.)
Static Analysis
Assume all in parameters require NT, all out params provide NT.
Write specialized handlers for any function where this is not the case (should not be too many. Default should be that strings are NT as soon as possible.)
O represents open strings, M represents maybe case (top of lattice).
Local analysis. Make sure we meet our own handler requirements, too.
Few false positives, as those that accept NT are specified. Probably will still get some FP from pointer magic.
Consider affects on STR03-A, STR07-A, and STR31-C
Combined attack (SA/DA/T)
Static analysis to generate test cases, dynamic analysis instruments the code that the test cases run on. Will have slightly different tradeoffs to SA. Good if we don't know the codebase well enough to create the handlers for non-NT functions. More work up front to create this kind of analysis, but reusable to many codebases. Provides the breadth of static analysis, the preciseness of dynamic analysis, and the repeatability of testing. Will have to think through this algorithm more carefully.
Rejected Strategies
Testing
It would probably be prohibitively expensive to come up with the test cases by hand.
Dynamic Analysis
It seems the analysis won't be very different from the static analysis, in which case, we should just do this statically.
Inspection
An inspection would essentially grep for known problem functions and inspect the usage. Obviously, this is extremely costly, as there would be a lot of false positives, and this does not scale well. There may also be many false negatives. Say Dev A inspects a function that returns an open string. Dev A considers it ok and documents it as such, perhaps this is one of the exception cases. Dev B might be inspecting another part of the code and might not realize that Dev A allowed an open string. It might be documented, but this is not very reliable. This might lead to a false sense of confidence that since the developers hand inspected every case that the code is fine, when in fact, a miscommunication can cause a defect.
References
[[ISO/IEC 9899-1999]] Section 7.1.1, "Definitions of terms," and Section 7.21, "String handling <string.h>"
[[Seacord 05]] Chapter 2, "Strings"
[[ISO/IEC TR 24731-2006]] Section 6.7.1.4, "The strncpy_s function"
[[Viega 05]] Section 5.2.14, "Miscalculated null termination"