How severe is CVE-2026-55209?

CVE-2026-55209 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-55209?

CVE-2026-55209 affects the following packages: resdata (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-55209?

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.

How do I detect CVE-2026-55209 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for resdata. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-55209 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-55209?

O3 pinpoints whether CVE-2026-55209 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-55209 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55209 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-55209 published, and has it been updated?

CVE-2026-55209 was published on August 18, 2026 and was last updated on August 19, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

CRITICAL severity

CVE-2026-55209

CRITICAL

CVE-2026-55209 is a critical-severity (CVSS 9.8) vulnerability in resdata. O3 Security confirms whether CVE-2026-55209 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

resdata has Classic Buffer Overflow, Improper Validation of Array Index, NULL Pointer Dereference and Out-of-bounds Read

Also known asPYSEC-2026-3694

Published

Aug 18, 2026

Updated

Aug 19, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Aug 19, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐍resdata

Real-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

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`resdata`	all versions	6.2.9

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for resdata. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-55209 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-55209. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

### 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.

O3 Security · Impact-Aware SCA

Is CVE-2026-55209 in your dependencies?

O3 detects CVE-2026-55209 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works