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C

C static code analysis

Unique rules to find Bugs, Vulnerabilities, Security Hotspots, and Code Smells in your C code

  • All rules 315
  • Vulnerability13
  • Bug76
  • Security Hotspot19
  • Code Smell207

  • Quick Fix 19
 
Tags
    Impact
      Clean code attribute
        1. Hard-coded secrets are security-sensitive

           Security Hotspot
        2. "sprintf" should not be used

           Security Hotspot
        3. Changing working directories without verifying the success is security-sensitive

           Security Hotspot
        4. Setting capabilities is security-sensitive

           Security Hotspot
        5. Using "tmpnam", "tmpnam_s" or "tmpnam_r" is security-sensitive

           Security Hotspot
        6. Using "strncpy" or "wcsncpy" is security-sensitive

           Security Hotspot
        7. Using "strncat" or "wcsncat" is security-sensitive

           Security Hotspot
        8. Using "strcat" or "wcscat" is security-sensitive

           Security Hotspot
        9. Using "strlen" or "wcslen" is security-sensitive

           Security Hotspot
        10. Changing directories improperly when using "chroot" is security-sensitive

           Security Hotspot
        11. Using "strcpy" or "wcscpy" is security-sensitive

           Security Hotspot
        12. Using publicly writable directories is security-sensitive

           Security Hotspot
        13. Using clear-text protocols is security-sensitive

           Security Hotspot
        14. Expanding archive files without controlling resource consumption is security-sensitive

           Security Hotspot
        15. Using weak hashing algorithms is security-sensitive

           Security Hotspot
        16. Setting loose POSIX file permissions is security-sensitive

           Security Hotspot
        17. Using pseudorandom number generators (PRNGs) is security-sensitive

           Security Hotspot
        18. Hard-coded passwords are security-sensitive

           Security Hotspot
        19. Using hardcoded IP addresses is security-sensitive

           Security Hotspot

        Using "strncat" or "wcsncat" is security-sensitive

        consistency - conventional
        security
        Security Hotspot
        • cwe
        • cert

        In C, a string is just a buffer of characters, normally using the null character as a sentinel for the end of the string. This means that the developer has to be aware of low-level details such as buffer sizes or having an extra character to store the final null character. Doing that correctly and consistently is notoriously difficult and any error can lead to a security vulnerability, for instance, giving access to sensitive data or allowing arbitrary code execution.

        The function char *strncat( char *restrict dest, const char *restrict src, size_t count ); appends the characters of string src at the end of dest, but only add count characters max. dest will always be null-terminated. The wcsncat does the same for wide characters, and should be used with the same guidelines.

        Ask Yourself Whether

        • There is a possibility that either the src or the dest pointer is null
        • The current string length of dest plus the current string length of src plus 1 (for the final null character) is larger than the size of the buffer pointer-to by src
        • There is a possibility that either string is not correctly null-terminated

        There is a risk if you answered yes to any of those questions.

        Recommended Secure Coding Practices

        • C11 provides, in its annex K, the strncat_s and the wcsncat_s that were designed as safer alternatives to strncat and wcsncat. It’s not recommended to use them in all circumstances because they introduce a runtime overhead and require to write more code for error handling, but they perform checks that will limit the consequences of calling the function with bad arguments.
        • Even if your compiler does not exactly support annex K, you probably have access to similar functions
        • If you are using strncat and wsncat as a safer version of strcat and wcscat, you should instead consider strcat_s and wcscat_s because these functions have several shortcomings:
          • It’s not easy to detect truncation
          • The count parameter is error-prone
          • Computing the count parameter typically requires computing the string length of dest, at which point other simpler alternatives exist

        Sensitive Code Example

        int f(char *src) {
          char dest[256];
          strcpy(dest, "Result: ");
          strncat(dest, src, sizeof dest); // Sensitive: passing the buffer size instead of the remaining size
          return doSomethingWith(dest);
        }
        

        Compliant Solution

        int f(char *src) {
          char result[] = "Result: ";
          char dest[256];
          strcpy(dest, result);
          strncat(dest, src, sizeof dest - sizeof result); // Compliant but may silently truncate
          return doSomethingWith(dest);
        }
        

        See

        • OWASP - Top 10 2021 Category A6 - Vulnerable and Outdated Components
        • OWASP - Top 10 2017 Category A9 - Using Components with Known Vulnerabilities
        • CWE - CWE-120 - Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
        • CERT, STR07-C. - Use the bounds-checking interfaces for string manipulation
        • STIG Viewer - Application Security and Development: V-222612 - The application must not be vulnerable to overflow attacks.
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