HDF5 szip filter EUVD-2026-115916

Only builds of HDF5 compiled with szip support (libaec or the szip library) are affected - builds without szip are not exploitable. Exploitation requires a victim user or application to read a dataset from an attacker-crafted HDF5 file whose szip chunk record is 4 bytes or shorter (at most the uncompressed-length header), triggering the underflowing length subtraction. Limiting factors: local attack vector (the file must be delivered to and opened on the host), mandatory user/application interaction (UI:P), the optional szip build dependency, and impact confined to denial of service (crash) with no confidentiality or integrity consequence.

This is a medium-severity, limited-impact issue rather than a top priority. The CVSS 4.0 base score is 4.7 with vector AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H: the attack vector is LOCAL (the malicious data must reach the host as a file), exploitation requires passive user interaction (UI:P - a victim must open/read the dataset) and carries an attack requirement (AT:P), and the only impact is availability (VA:H) - no confidentiality or integrity loss. The vuln.today decision label is 'this_month', not act_now/emergency, which aligns with the modest score. There is no CISA KEV listing, so there is no confirmed active exploitation. CVSS exploit maturity is marked Proof-of-Concept (E:P), but the only reference supplied is the vendor fix PR (HDFGroup/hdf5#6585), not working exploit code - so POC maturity is asserted by the metric while no exploit artifact is present in the provided data. EPSS is not provided. Net: a crafted-file denial-of-service in a build-optional code path; real but low urgency, suitable for routine patching rather than emergency response. Signals are internally consistent (local vector, DoS-only, no KEV, this_month), with no contradictions requiring vendor verification.

An attacker crafts an HDF5 file containing a szip-filtered chunk whose stored record is shorter than its 4-byte uncompressed-length header, then gets a user or application to read a dataset from that file (UI:P). The length subtraction (nbytes - 4) wraps to a very large value and the szip decompressor reads far past the end of the chunk buffer, crashing the process. No separate working exploit is referenced in the available data, though CVSS marks exploit maturity as Proof-of-Concept (E:P).