CVE-2026-55209: Resdata Resdata Has Classic Buffer Overflow, Vulnerability

CRITICAL
Advisory Identifier: GHSA-pr85-w493-9w3x
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CVSS 9.8
CWE-125 CWE-120 CWE-129 CWE-476
Published
Advisory Summary

CVE-2026-55209 is a CRITICAL (CVSS 9.8) resdata has classic buffer overflow, vulnerability (CWE-125: Out-of-bounds Read) affecting Resdata libraries in the PyPI ecosystem. The issue involves resdata has classic buffer overflow, improper validation of array index, null pointer dereference and out-of-bounds read. Remediation is available by upgrading affected packages to version 6.2.9.

CVE-2026-55209 at a Glance

CVE Identifier CVE-2026-55209
GHSA Identifier GHSA-pr85-w493-9w3x
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-125: Out-of-bounds Read
Affected Product Resdata
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-55209

To remediate this vulnerability, upgrade all affected Resdata dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

resdata fixed: 6.2.9 
pip install resdata>=6.2.9
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show resdata

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-55209, inspect your installed packages using pip:

pip show resdata

Analyze the terminal output to locate any version of Resdata in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.2.9), your application is affected.

Note: The pip show resdata command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-125: Out-of-bounds Read, where the product reads data past the end, or before the beginning, of the intended buffer. In Resdata, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Prior to version 6.2.9 resdata would not correctly validate input in GRDECL files. The severity rating assumes that resdata is used to parse untrused files in a networking context such as a webservice. ### Patches The bug has been patched starting with version 6.2.9.

CVE-2026-55209 Affected Resdata Versions

1 component(s)
Fixed Versions:
6.2.9
Product / Package Ecosystem Affected Versions Fixed Version
resdata
pypi/resdata
PyPI
< 6.2.9
6.2.9

References

GitHub Advisory / Wiki ADVISORY
https://github.com/equinor/resdata/security/advisories/GHSA-pr85-w493-9w3x
Resdata Source Repository REPOSITORY
https://github.com/equinor/resdata
Resdata Release RELEASE
https://github.com/equinor/resdata/releases/tag/6.2.9

Frequently Asked Questions

What is CVE-2026-55209?
CVE-2026-55209 is a security vulnerability in Resdata involving resdata has Classic Buffer Overflow, Improper Validation of Array Index, NULL Pointer Dereference and Out-of-bounds Read under CWE-125: Out-of-bounds Read.
Which Resdata versions are affected?
Affected versions include releases prior to 6.2.9 across affected packages: resdata.
What version fixes CVE-2026-55209?
Upgrading to 6.2.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is resdata affected?
Yes, resdata is affected in releases prior to 6.2.9. Upgrade your dependency to 6.2.9 or later.
What is the CVSS score of CVE-2026-55209?
CVE-2026-55209 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-55209?
CVE-2026-55209 is classified under CWE-125: Out-of-bounds Read (The product reads data past the end, or before the beginning, of the intended buffer.).
How can I check PyPI dependencies for CVE-2026-55209?
Run the dependency tree command: 'pip show resdata'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-pr85-w493-9w3x",
  "modified" : "2026-08-18T20:11:04Z",
  "published" : "2026-08-18T20:11:04Z",
  "aliases" : [ "CVE-2026-55209" ],
  "summary" : "resdata has Classic Buffer Overflow, Improper Validation of Array Index, NULL Pointer Dereference and Out-of-bounds Read",
  "details" : "### Impact\nPrior to version 6.2.9 resdata would not correctly validate input in GRDECL files. The severity rating assumes that resdata is used to parse untrused files in a networking context such as a webservice.\n\n### Patches\nThe bug has been patched starting with version 6.2.9.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "resdata"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.2.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/equinor/resdata/security/advisories/GHSA-pr85-w493-9w3x"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/equinor/resdata"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/equinor/resdata/releases/tag/6.2.9"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-120", "CWE-125", "CWE-129", "CWE-476" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-18T20:11:04Z",
    "nvd_published_at" : null
  }
}