GHSA-3h9h-qfvw-98hq

Описание

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):

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:

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