heap write in hashcat filehandling.c fgetl()

Executive Summary

This is an off-by-one heap buffer overflow in hashcat's fgetl() function. When a line in a hash file, potfile, or wordlist is exactly the size of the buffer (HCBUFSIZ_LARGE), the function writes a null terminator one byte past the buffer's end. This corrupts heap memory and could lead to crashes or other unintended behavior.

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Detection Guidance

Check if hashcat version 7.1.2 or earlier is installed. Examine input files (hash files, potfiles, wordlists) for lines exactly 16,777,216 bytes long. Monitor for SIGSEGV or ASAN heap-buffer-overflow errors during hashcat operations.

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Impact Analysis

An attacker could exploit this by providing a specially crafted file to cause heap corruption. This may result in denial of service, crashes, or potentially allow arbitrary code execution depending on heap layout. The impact depends on the system's memory management and heap state.

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Mitigation Strategies

Upgrade hashcat to a version beyond 7.1.2 where the fgetl() buffer overflow is fixed. Avoid using untrusted input files for hashcat operations until patched.

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