OpenEXR Makes Use of Uninitialized Memory
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):
==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<Imf_4_0::Slice, std::__1::allocator<Imf_4_0::Slice> > 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:
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/pocImpact
- 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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | openexr | >= 3.3.0, < 3.3.6, >= 3.4.0, < 3.4.3 | 3.3.6, 3.4.3 |
References
- https://github.com/AcademySoftwareFoundation/openexr/security/advisories/GHSA-3h9h-qfvw-98hq
- https://nvd.nist.gov/vuln/detail/CVE-2025-64181
- https://github.com/AcademySoftwareFoundation/openexr
- https://github.com/user-attachments/files/23024726/archive0.zip
- https://github.com/user-attachments/files/23024736/archive1.zip
- https://github.com/user-attachments/files/23024740/archive2.zip
- https://github.com/user-attachments/files/23024744/archive3.zip
- https://github.com/user-attachments/files/23024746/archive4.zip
- https://pypi.org/project/openexr
- https://github.com/advisories/GHSA-3h9h-qfvw-98hq
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-457- Platform
- Python (PyPI)
- Package
openexr- Disclosed
- 06.04.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2843 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-3h9h-qfvw-98hq - CC BY 4.0
Vulnerability history: openexr
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 15
- First → latest
- 05.2022 04.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 7
- Medium 7
- Low 1
Disclosures per year
- 2022: 2
- 2023: 0
- 2024: 0
- 2025: 4
- 2026: 9
-
OpenEXR Makes Use of Uninitialized Memory this entry
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