The vulnerability exists in the H5Z__filter_fletcher32 function within H5Zfletcher32.c of the HDF5 library through version 2.3.0. It computes the data length for checksum calculation by subtracting a fixed 4-byte checksum size from the input buffer size without checking if the buffer is at least 4 bytes. This leads to a size_t underflow if the buffer is smaller than 4 bytes, resulting in a massively out-of-bounds read in H5_checksum_fletcher32. An attacker can exploit this by crafting an HDF5 file with a Fletcher32-filtered chunk smaller than 4 bytes, causing a denial of service (application crash) when the file is read via H5Dread, including through utilities like h5ls or h5dump.

This vulnerability allows an attacker to cause a denial of service by crashing applications that use the vulnerable HDF5 library when processing maliciously crafted HDF5 files. The impact is limited to denial of service; there is no indication of code execution or data corruption beyond the crash.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid processing untrusted HDF5 files with Fletcher32-filtered chunks smaller than 4 bytes. Monitor vendor communications for updates on patches or official fixes.