CVE-2026-26197: HDF5 Library Buffer Overflow Vulnerability

CVE-2026-26197 Overview

CVE-2026-26197 is an out-of-bounds read vulnerability [CWE-125] in the HDF5 library, a high-performance library and file format specification that implements the HDF5 data model. The flaw resides in how HDF5 parses array datatypes when the stored full size, element count, and element size fields are inconsistent. Processing a maliciously crafted HDF5 file triggers an out-of-bounds read in the parser. The vulnerability requires user interaction to open a tampered file and only manifests when files have been deliberately modified by an attacker.

Critical Impact
Attackers who deliver a crafted HDF5 file can trigger out-of-bounds memory reads, causing process crashes or potential information disclosure in applications consuming HDF5 data.

Affected Products

HDF5 library (The HDF Group)
Applications and scientific tooling that parse untrusted HDF5 files
Downstream data pipelines relying on HDF5 for storage and interchange

Discovery Timeline

2026-07-20 - CVE-2026-26197 published to NVD
2026-07-23 - Last updated in NVD database

Technical Details for CVE-2026-26197

Vulnerability Analysis

HDF5 stores an array datatype using three independent fields: the full datatype size (dt->shared->size), the number of elements (dt->shared->u.array.nelem), and the element size (dt->shared->parent->shared->size). The parser assumes the invariant element size * nelem = full size holds. When any single field is tampered with, that invariant breaks and the library reads memory beyond the intended buffer boundary. The specific type of out-of-bounds read depends on which field the attacker corrupted.

Root Cause

The root cause is missing validation of the relationship between the three size fields when deserializing an array datatype. The code trusts values read from the file and derefences memory using them without cross-checking that the arithmetic invariant holds. This is a classic parser trust boundary failure in binary format handling.

Attack Vector

Exploitation requires an attacker to deliver a maliciously altered HDF5 file to a victim who then opens it with an affected version of the library. The condition cannot arise from normal HDF5 usage because writers produce consistent size, element count, and element size metadata. Attack scenarios include shared scientific datasets, model files, and telemetry archives ingested by automated pipelines. The vulnerability enables denial of service through crashes and potentially adjacent memory disclosure.

No verified public exploit code exists for this issue. See the GitHub Security Advisory (GHSA-gh44-7wpq-622f) for technical details from the maintainers.

Detection Methods for CVE-2026-26197

Indicators of Compromise

Crashes, segmentation faults, or sanitizer reports in processes loading HDF5 files (.h5, .hdf5, .he5)
HDF5 files whose array datatype header fails the element_size * nelem == full_size check
Unexpected file reads from untrusted sources followed by abnormal termination of analytics or ML workloads

Detection Strategies

Statically scan HDF5 files for array datatype messages and validate the size relationship before ingestion
Run HDF5-parsing workloads under AddressSanitizer during pre-production testing to surface out-of-bounds reads
Monitor endpoint telemetry for repeated crash signatures in processes linked against libhdf5

Monitoring Recommendations

Alert on abnormal termination of scientific computing, machine learning, or data ingestion services that consume HDF5 input
Log the origin and hash of HDF5 files entering shared storage and processing clusters
Track HDF5 library versions across build environments and container images to identify unpatched deployments

How to Mitigate CVE-2026-26197

Immediate Actions Required

Inventory all systems and applications linking against the HDF5 library and identify library versions in use
Restrict HDF5 file ingestion to trusted sources until the library is updated
Isolate HDF5 parsing workloads in sandboxes or containers with restricted memory access to limit blast radius

Patch Information

Refer to the HDF5 GitHub Security Advisory GHSA-gh44-7wpq-622f for the fixed release version and patch commits from The HDF Group. Rebuild any statically linked applications and container images against the patched library.

Workarounds

Validate HDF5 files with a checksum allowlist before parsing to reject unexpected content
Reject or quarantine HDF5 files received from external or unauthenticated sources
Run HDF5 consumers with least privilege and enable operating system exploit mitigations such as ASLR and stack canaries

bash

# Verify installed HDF5 library version on Linux
ldconfig -p | grep libhdf5
h5cc -showconfig | grep -i version