How severe is CVE-2026-27942?

No CVSS score has been assigned to CVE-2026-27942 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-27942?

CVE-2026-27942 affects the following packages: fast-xml-parser (npm), fast-xml-parser (npm). Ecosystems affected: npm.

How do I fix CVE-2026-27942?

Update fast-xml-parser to 5.3.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27942 is resolved across your whole dependency graph.

How do I detect CVE-2026-27942 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-xml-parser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-27942 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-2026-27942?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27942 can be triaged on real exposure rather than presence alone.

Is CVE-2026-27942 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-27942 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.

What is the EPSS score for CVE-2026-27942?

CVE-2026-27942 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-27942?

CVE-2026-27942 is classified as CWE-120 (CWE-120). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-27942 published, and has it been updated?

CVE-2026-27942 was published on February 26, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-27942 — fast-xml-parser

Fix: NaturalIntelligence/fast-xml-parser@c13a961

CVE-2026-27942 is a CWE-120 vulnerability in fast-xml-parser. A fix is available for fast-xml-parser — see the affected versions and patch details below.

fast-xml-parser has stack overflow in XMLBuilder with preserveOrder

Also known asGHSA-fj3w-jwp8-x2g3

Published

Feb 26, 2026

Updated

Aug 12, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Sep 20, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

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-2026-27942.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

5Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

fast-xml-parsernpm

57.7Mdownloads / week

Description

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. Prior to version 5.3.8, the application crashes with stack overflow when user use XML builder with preserveOrder:true. Version 5.3.8 fixes the issue. As a workaround, use XML builder with preserveOrder:false or check the input data before passing to builder.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`fast-xml-parser`	≥ 5.0.0&&< 5.3.8	5.3.8`npm install fast-xml-parser@5.3.8`
📦npm	`fast-xml-parser`	≥ 4.0.0-beta.0&&< 4.5.4	4.5.4`npm install fast-xml-parser@4.5.4`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fast-xml-parser, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fast-xml-parser to 5.3.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27942 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27942 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-27942. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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 HatModerate

The flaw affects the XML builder component of the fast-xml-parser library and is triggered only when the preserveOrder option is explicitly enabled. In Red Hat–shipped configurations, this option is not enabled by default, and the vulnerable code path is therefore not exercised under typical deployments. The…

Product	Fixed in	Advisory
Red Hat Advanced Cluster Security 4.8	`advanced-cluster-security/rhacs-main-rhel8:1775594119`	RHSA-2026:7110
Red Hat Advanced Cluster Security 4.9	`advanced-cluster-security/rhacs-main-rhel8:1775594284`	RHSA-2026:7128
Red Hat Developer Hub 1.8	`rhdh/rhdh-hub-rhel9:1774545605`	RHSA-2026:6174
Red Hat Developer Hub 1.9	`rhdh/rhdh-hub-rhel9:1775140647`	RHSA-2026:6802
Red Hat Openshift Data Foundation 4.18	`odf4/cephcsi-rhel9:1783676191`	RHSA-2026:41941
Red Hat Openshift Data Foundation 4.19	`odf4/cephcsi-rhel9:1783684360`	RHSA-2026:41944
Red Hat Openshift Data Foundation 4.20	`odf4/cephcsi-rhel9:1775822432`	RHSA-2026:12277
Red Hat Openshift Data Foundation 4.20	`odf4/cephcsi-rhel9:1783667125`	RHSA-2026:40984

Frequently Asked Questions

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. Prior to version 5.3.8, the application crashes with stack overflow when user use XML builder with `preserveOrder:true`. Version 5.3.8 fixes the issue. As a workaround, use XML builder with `preserveOrder:false` or check the input data before passing to builder.

O3 Security · Impact-Aware SCA

Is CVE-2026-27942 in your dependencies?

O3 Security finds CVE-2026-27942 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works