h5io: Arbitrary code execution in read_hdf5 (CVE-2026-120499)

The h5io Python library, specifically in versions prior to 0.2.6, contains a code injection vulnerability within the read_hdf5() function. An attacker can craft a malicious HDF5 file containing specific node structures that, when processed, lead to arbitrary code execution. The vulnerability stems from three primary mechanisms:

1. The timezone node is passed to eval() with builtins enabled.
2. class or custom-object nodes allow for arbitrary module imports via _import_class().
3. pd_dataframe or pd_series nodes contain pickled objects that are insecurely deserialized by pandas.

Impact

Successful exploitation allows for arbitrary code execution with the privileges of the application process that invokes the read_hdf5() function.

Recommendation

• Upgrade the h5io library to version 0.2.6 or later immediately.
• Audit applications that process externally sourced HDF5 files using h5io.
• Implement sandboxing or containerization for untrusted file processing workloads to limit the impact of code execution vulnerabilities.