Daily security quiz #13

Question for 2026-11-13. Read the code and pick the most serious security vulnerability.

This function logs error messages. msg comes from a user request. What is the most serious vulnerability?

1#include <stdio.h>
2 
3void log_error(FILE *log, const char *msg) {
4    fprintf(log, "[error] ");
5    fprintf(log, msg);
6    fprintf(log, "\n");
7}

1. ALogs are lost because fflush is not called
2. BUser input is used as a format string, allowing memory to be read and written with %x and %n
3. CThe FILE pointer is not checked for NULL
4. DThe logs have no dates