mrrobots18/gguf-poc-alignment-nullderef

GGUF Parser NULL Pointer Dereference -- PoC

Vulnerability: NULL Pointer Dereference via attacker-controlled general.alignment field in gguf_init_from_file_impl()

Target: llama.cpp / ggml GGUF parser
Commit tested: b9da444 (latest main)
Severity: HIGH -- SEGV confirmed by AddressSanitizer
Submitted to: huntr.com bug bounty ($3,000-$4,000 tier)

Files

File	Description
poc1_huge_alignment.gguf	518-byte malicious GGUF triggering SEGV crash
generate_malicious.py	Python 3 PoC generator (no dependencies)
ASAN_output.txt	Full AddressSanitizer + UBSan crash output

Quick Reproduction

# Clone and build with ASAN
git clone --depth=1 https://github.com/ggerganov/llama.cpp
cd llama.cpp

cmake -B build-asan \
  -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_CXX_FLAGS="-fsanitize=address,undefined -g" \
  -DCMAKE_C_FLAGS="-fsanitize=address,undefined -g" \
  -DGGML_NATIVE=OFF

cmake --build build-asan --target llama-gguf -j4

# Run PoC
export LD_LIBRARY_PATH=./build-asan/bin
./build-asan/bin/llama-gguf poc1_huge_alignment.gguf r

# Expected:
# AddressSanitizer: SEGV on unknown address 0x000000000000
# SUMMARY: AddressSanitizer: SEGV gguf.cpp:869 in gguf_get_version

Root Cause (gguf.cpp:559)

// VULNERABLE: only power-of-2 check, NO upper bound
if (ctx->alignment == 0 || (ctx->alignment & (ctx->alignment - 1)) != 0) {
    return nullptr;
}
// With alignment=2^31, fseek jumps to 2GB offset in a 518-byte file
// fread() returns 0, parser returns nullptr, caller dereferences it -> SEGV

Fix

const size_t GGUF_MAX_ALIGNMENT = (1u << 20);  // 1MB max
if (ctx->alignment == 0 ||
    (ctx->alignment & (ctx->alignment - 1)) != 0 ||
    ctx->alignment > GGUF_MAX_ALIGNMENT) {      // ADD THIS
    return nullptr;
}

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