Format String Vulnerabilities
A security flaw that allows attackers to manipulate program output by injecting format specifiers.
Understanding Format String Vulnerabilities
This occurs when an application directly accepts user-controlled format specifiers (like %s, %x, %n) in functions like printf(), without proper validation. Attackers exploit this to access memory locations or manipulate program execution.
How Format String Attacks Work
Reading Arbitrary Memory – Using
%xor%sto leak sensitive data from memory.Memory Corruption & Overwriting Variables –
%nallows writing arbitrary values into memory, altering execution flow.Gaining Code Execution – Attackers inject shellcode by modifying function return addresses.
Best Practices for Preventing Format String Vulnerabilities
1. Use Safe Formatting Functions
Replace printf() with snprintf() or sprintf_s(), which prevent format injection.
2. Implement Input Validation & Sanitization
Restrict user input and use whitelisting approaches.
3. Compile with Security Flags
Enable FORTIFY_SOURCE and Address Space Layout Randomization (ASLR) to mitigate exploits.