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CVE-2026-19027: HDF5 out-of-bounds heap read in N-Bit filter decompression

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-06 · updated 2026-10-23
• Weakness: CWE-125

Description

The H5Z__nbit_decompress_one_byte, H5Z__nbit_decompress_one_nooptype, and H5Z__nbit_decompress_one_atomic functions in H5Znbit.c in HDF5 prior to 2.3.0 advance a read index into the compressed chunk buffer without bounding it against the buffer's actual size. This allows attackers to cause an out-of-bounds heap read, and in constrained cases disclosure of adjacent heap memory into decompressed dataset values, via a crafted HDF5 file whose N-Bit filter parameters describe more decompressed data than the stored compressed chunk actually contains, triggered via H5Dread, e.g. by the h5ls or h5repack tools.

Affected products

• HDF5: through 2.3.0

References

• https://github.com/HDFGroup/hdf5/issues/6489
• https://github.com/HDFGroup/hdf5/issues/6492
• https://github.com/HDFGroup/hdf5/pull/6497
• https://github.com/HDFGroup/hdf5/issues/6489

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