CVE-2026-55209 is a critical-severity (CVSS 9.8) CWE-120 vulnerability in resdata. A fix is available for resdata — see the affected versions and patch details below.
resdata insufficiently validates untrusted GRDECL files
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55209.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-55209 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 382,205 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
resdataReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
resdata is software for reading and writing result files from the Eclipse reservoir simulator. Prior to 6.2.9, resdata insufficiently validates numeric fields, grid dimensions, keyword sizes, and array indexes while parsing untrusted GRDECL files in lib/resdata/rd_kw_grdecl.cpp and lib/resdata/rd_grid.cpp. Malformed COORD, ZCORN, CORSNUM, ACTNUM, or MAPAXES data can reach rd_grid_alloc_GRDECL_kw__ with inconsistent lengths, while unbounded floating-point conversion can exceed the intended parser buffer. In a network service that accepts untrusted GRDECL files, these conditions can cause a classic buffer overflow, out-of-bounds reads, invalid array access, NULL pointer dereference, memory corruption, or service termination. This issue is fixed in version 6.2.9.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | resdata | all versions | 6.2.9pip install --upgrade 'resdata==6.2.9' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for resdata, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update resdata to 6.2.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55209 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Frequently Asked Questions
Is CVE-2026-55209 in your dependencies?
Find it across PyPI, including transitive dependencies.