CVE-2026-120755: Integer Underflow Leads to Out-of-Bounds Read via Truncated Chunk in HDF5 Szip Filter

HDF5 through 2.2.0 contains an out-of-bounds read vulnerability in H5Zfilterszip() in src/H5Zszip.c. When decoding a szip-compressed chunk, the function subtracts the 4-byte uncompressed-length header from the chunk length without first verifying that the chunk is at least 4 bytes long. A truncated or corrupted chunk shorter than the header causes the length calculation to wrap around to a very large value, and the decompressor reads far past the end of the chunk buffer. An attacker who can get a user or application to read a dataset from a crafted HDF5 file can cause a denial of service. Only builds with szip support (libaec or the szip library) are affected.