GHSA-3h9h-qfvw-98hq OpenEXR Makes Use of Uninitialized Memory

• PyPI OpenEXR: >= 3.3.0, < 3.3.6 → fixed in 3.3.6 • PyPI OpenEXR: >= 3.4.0, < 3.4.3 → fixed in 3.4.3

Summary While fuzzing `openexr_exrcheck_fuzzer`, Valgrind reports a conditional branch depending on uninitialized data inside `generic_unpack`. This indicates a use of uninitialized memory (CWE-457). The issue is reproducible with the current OSS-Fuzz harness and a single-file PoC. Details Environment: • Tooling: `valgrind --tool=memcheck --track-origins=yes` • Target: `openexr_exrcheck_fuzzer` • OS: Ubuntu 20.04.6 LTS focal x86_64 • openexr version and Git-commit hash: ` openexr 3.4.2 | commit fd657e8a41e157e5841c7cc2e2a5efe094b069a1 (grafted, HEAD -> main, origin/main, origin/HEAD)` Function: `generic_unpack` Possible root cause (based on observed symptoms): The unpacker is branching on bytes in a scratch buffer that were never written because the decode step didn’t fully populate it. • The first use flagged is in `generic_unpack()`. That function reads from the decompressed/expanded pixel buffer to scatter data into the framebuffer. A “conditional jump depends on uninitialised value(s)” means it’s consulting bytes in that buffer before they were written. • Valgrind says the uninitialised value “was created by a heap allocation (malloc)”, not the stack: this matches a per-tile/per-scanline decode scratch buffer allocated in `exr_decoding_run()`. Valgrind Trace (top frames): ```bash ==454== Conditional jump or move depends on uninitialised value(s) ==454== at 0x4539BE: generic_unpack (in /out/openexr_exrcheck_fuzzer) ==454== by 0x44B85F: exr_decoding_run (in /out/openexr_exrcheck_fuzzer) ==454== by 0x38BC5F: Imf_4_0::(anonymous namespace)::TileProcess::run_decode(_priv_exr_context_t const*, int, Imf_4_0::FrameBuffer const*, std::__1::vector > const&) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x388BE1: Imf_4_0::TiledInputFile::Data::readTiles(int, int, int, int, int, int) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x388619: Imf_4_0::TiledInputFile::readTiles(int, int, int, int, int, int) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x353755: Imf_4_0::InputFile::Data::bufferedReadPixels(int, int) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x352286: Imf_4_0::InputFile::readPixels(int) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x3190FA: Imf_4_0::(anonymous namespace)::readMultiPart(Imf_4_0::MultiPartInputFile&, bool, bool) (in /out/openexr_exrcheck_fuzzer) ==454== by 0x314C4D: Imf_4_0::checkOpenEXRFile(char const*, unsigned long, bool, bool, bool) (in /out/openexr_exrcheck_fuzzer) ==454== Uninitialised value was created by a heap allocation at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so) ``` PoC In the attached archive, you will find: • The executable used for our tests. • The testcase used to trigger the bug. To observe the bug, simply run the OSS-Fuzz helper script: ```bash git clone https://github.com/google/oss-fuzz.git cd oss-fuzz python3 infra/helper.py build_image openexr python3 infra/helper.py build_fuzzers --sanitizer=none openexr python3 infra/helper.py shell openexr apt update && apt install -y valgrind ulimit -n 65535 valgrind --tool=memcheck --track-origins=yes /out/openexr_exrcheck_fuzzer /path/to/poc ``` Impact • Undefined Behavior • Potential crash • Denial of Service Credit: Aldo Ristori archive0.zip Update Note: Other saved testcases from the fuzzing campaign trigger the same underlying bug, but with a different manifestation. So there is one root cause (missing post-decode validation / zero-init before any unpack), with different call-sites. Below there are several archives, formatted like the previous one, that reproduce the other test cases. Other observed sinks (distinct manifestations of the same bug): Deep pointers path: generic_unpack_deep_pointers (deep scanline/tiled) archive1.zip Deep sample table path: unpack_sample_table (deep scanline) archive2.zip Half conversion path: half_to_float_buffer_f16c via unpack_half_to_float_3chan_planar archive3.zip Deep compositing: CompositeDeepScanLine::readPixels → ThreadPool::addTask → LineCompositeTask::execute archive4.zip