CVE-2026-120499 — h5io
Fix: h5io/h5io@afff1d6CVE-2026-120499 is a CWE-95 vulnerability. A fix is available — see the affected versions and patch details below.
h5io before 0.2.6 Arbitrary Code Execution via read_hdf5
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-120499.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Description
h5io before 0.2.6 contains a code injection vulnerability in read_hdf5() that allows attackers to execute arbitrary code by supplying a crafted HDF5 file. Attackers can store Python code in a node titled timezone, which _triage_read() passes to eval() with builtins reachable, name an arbitrary module in class or custom-object nodes that _import_class() imports, or place pickled objects in pd_dataframe or pd_series nodes that pandas deserializes on read.
Detection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Fix
Upgrade the affected component to the fixed release for CVE-2026-120499, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat rates this vulnerability as Important severity because an attacker can achieve arbitrary execution within the process context without prior privileges, although exploitation requires local interaction to load malicious data. The affected library is not part of default system installations and is typically…
Do not load or process HDF5 files from untrusted or unverified external sources. If processing untrusted datasets is required, execute workloads within an isolated container or restricted sandbox running under an unprivileged user account with minimal access to local storage and network resources. Caveat: Sandboxing or container isolation mitigates lateral movement and host compromise but does not prevent malicious code execution within the isolated container boundary itself.Source: Red Hat security advisory for CVE-2026-120499 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-120499 in your dependencies?
Find it across your dependency tree, including transitive dependencies.