CVE-2025-64181

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/poc

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

• Undefined Behavior
• Potential crash
• Denial of Service

Credit: Aldo Ristori
archive0.zip

CVE-2025-64181 has a CVSS score of 7.5 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.3.6, 3.4.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-64181? CVE-2025-64181 is a low-severity security vulnerability in OpenEXR (pip), affecting versions >= 3.3.0, < 3.3.6. It is fixed in 3.3.6, 3.4.3.
2. How severe is CVE-2025-64181? CVE-2025-64181 has a CVSS score of 7.5 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of OpenEXR are affected by CVE-2025-64181? OpenEXR (pip) versions >= 3.3.0, < 3.3.6 is affected.
4. Is there a fix for CVE-2025-64181? Yes. CVE-2025-64181 is fixed in 3.3.6, 3.4.3. Upgrade to this version or later.
5. Is CVE-2025-64181 exploitable, and should I be worried? Whether CVE-2025-64181 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-64181 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-64181?
   • Upgrade OpenEXR to 3.3.6 or later
   • Upgrade OpenEXR to 3.4.3 or later