GHSA-6hgw-6x87-578x

## Summary - **Target:** ImageMagick (commit `ecc9a5eb456747374bae8e07038ba10b3d8821b3`) - **Type:** Undefined Behavior (function-type-mismatch) in splay tree cloning callback - **Impact:** Deterministic abort under UBSan (DoS in sanitizer builds). No crash in a non-sanitized build; likely low security impact. - **Trigger:** Minimal **2-byte** input parsed via MagickWand, then coalescing. ## Environment OS: macOS (Apple Silicon/arm64) Homebrew clang version 20.1.8 Target: arm64-apple-darwin24.5.0 Thread model: posix InstalledDir: /opt/homebrew/Cellar/llvm/20.1.8/bin Configuration file: /opt/homebrew/etc/clang/arm64-apple-darwin24.cfg Homebrew ImageMagick: `magick -version` → `ImageMagick 7.1.2-0 Q16-HDRI aarch64` pkg-config: `MagickWand-7.Q16HDRI` version `7.1.2` Library configure flags (capsule build): ./configure --disable-shared --enable-static --without-modules --without-magick-plus-plus --disable-openmp --without-perl --without-x --with-png=yes --without-jpeg --without-tiff --without-xml --without-lqr --without-gslib Harness compile flags: -fsanitize=fuzzer,address,undefined -fno-omit-frame-pointer pkg-config cflags/libs supplied: -I<...>/include/ImageMagick-7 -DMAGICKCORE_HDRI_ENABLE=1 -DMAGICKCORE_QUANTUM_DEPTH=16 -DMAGICKCORE_CHANNEL_MASK_DEPTH=32 and linked against MagickWand-7.Q16HDRI and MagickCore-7.Q16HDRI Sanitizer runtime: ASan+UBSan defaults. Repro also with `UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1` ## PoC - **Bytes (hex):** `1c 02` - **Base64:** `HAI=` - **sha256 (optional):** <fill in> ## Reproduction Create PoC: `printf '\x1c\x02' > poc.bin` Option A: libFuzzer harness - Run once: `./harness_ImageMagick_... -runs=1 ./poc.bin` - Expected: UBSan aborts with function-type-mismatch at `MagickCore/splay-tree.c:372:43`. Option B: standalone reproducer (C) - Compile (ensure `PKG_CONFIG_PATH` points to your ImageMagick if needed): /opt/homebrew/opt/llvm/bin/clang -g -O1 -fsanitize=address,undefined $(/opt/homebrew/bin/pkg-config --cflags MagickWand-7.Q16HDRI) repro.c -o repro $(/opt/homebrew/bin/pkg-config --libs MagickWand-7.Q16HDRI) - Run: UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1 ./repro ./poc.bin Observed output (excerpt) MagickCore/splay-tree.c:372:43: runtime error: call to function ConstantString through pointer to incorrect function type 'void *(*)(void *)' string.c:680: note: ConstantString defined here #0 CloneSplayTree splay-tree.c:372 #1 CloneImageProfiles profile.c:159 #2 CloneImage image.c:832 #3 CoalesceImages layer.c:269 #4 MagickCoalesceImages magick-image.c:1665 #5 main repro.c:XX Root cause The splay tree clone callback expects a function pointer of type `void *(*)(void *)`. ConstantString has a different signature (`char *ConstantString(const char *)`). Calling through the mismatched function type is undefined behavior in C and triggers UBSan’s function-type-mismatch. The path is exercised during coalescing: CloneImage → CloneImageProfiles → CloneSplayTree. Scope Reproduces with a minimal, sanitizer-instrumented, PNG-enabled build and delegates disabled (policy.xml), suggesting the issue is in MagickCore rather than external delegates. Suggested fix (sketch) Use a wrapper that matches the expected callback prototype, or adjust the splay-tree callback typedef for const-correctness. For example: static void *CloneStringShim(const void *p) { return (void *) ConstantString((const char *) p); } /* When setting splay-tree clone_value, use CloneStringShim instead of ConstantString. */ Alternatively, update the clone callback typedefs to use const void* consistently (and return void*) and ensure callers pass a correctly typed wrapper. Artifacts Minimised PoC: attached (poc.bin, 2 bytes; base64 HAI=) Harness source and exact build command (attached) Full UBSan trace (attached) Commit SHA and configure flags (above) Credits Discovered by: Lumina Mescuwa Method: libFuzzer + UBSan Verification - UBSan build: Reproduces with `halt_on_error=1`; aborts at `MagickCore/splay-tree.c:372`. - Non-sanitized Homebrew build (macOS arm64, clang 20.1.8): No crash; repro completes silently.