---
title: "CVE-2026-55209: resdata has Classic Buffer Overflow, Improper Validation of Array Index, NULL Pointer Dereference and Out-of-bounds Read"
url: https://erroneo.us/security/cve/CVE-2026-55209/
description: "CVE-2026-55209 (resdata (PyPI)): resdata is software for reading and writing result files from the Eclipse reservoir simulator. Prior to 6.2.9, resdata…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-14
date_modified: 2026-09-14
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-55209"
kev: false
cvss: 9.8
epss: 0.0078
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-55209: resdata has Classic Buffer Overflow, Improper Validation of Array Index, NULL Pointer Dereference and Out-of-bounds Read

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.8% , percentile 55: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 55% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes resdata (PyPI) < 6.2.9, fixed in 6.2.9 . Check your lockfile, including transitive dependencies.

## What it is

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/rdkwgrdecl.cpp and lib/resdata/rdgrid.cpp. Malformed COORD, ZCORN, CORSNUM, ACTNUM, or MAPAXES data can reach rdgridallocGRDECLkw 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

- PyPI `resdata` < 6.2.9 → fixed: 6.2.9

## Affected products (CVE record)

- equinor resdata: < 6.2.9

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.78% probability of exploitation activity in the next 30 days; percentile 55.

## Sources

- [GitHub Advisory GHSA-pr85-w493-9w3x](https://github.com/advisories/GHSA-pr85-w493-9w3x)
- [CVE.org record CVE-2026-55209](https://www.cve.org/CVERecord?id=CVE-2026-55209)
- [NVD entry CVE-2026-55209](https://nvd.nist.gov/vuln/detail/CVE-2026-55209)
- [github.com](https://github.com/equinor/resdata/security/advisories/GHSA-pr85-w493-9w3x)
- [github.com](https://github.com/equinor/resdata/pull/1166)
- [github.com](https://github.com/equinor/resdata/commit/9f8fd6db472e0696080b768389914d60a453904f)
- [github.com](https://github.com/equinor/resdata/commit/d3f45828e9413506b8e8160a9304f4b7b06dcefc)
- [github.com](https://github.com/equinor/resdata/commit/ee8cc12b026d945df3077bc98e211ee45f80a433)
- [github.com](https://github.com/equinor/resdata/releases/tag/6.2.9)

---
Source page: https://erroneo.us/security/cve/CVE-2026-55209/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt