CVE-2026-26278

Naturalintelligence Fast-xml-parser vulnerability

7.5 HIGHPublic exploitEPSS 0.99%

Published19 Feb 2026

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. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Naturalintelligence Fast-xml-parser≥ 4.1.3 < 5.3.6

Remediation

Fixed in

Naturalintelligence Fast-xml-parser≥ 5.3.6

Patch & vendor advisories

References

and 4 more references

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-26278 being actively exploited?

CVE-2026-26278 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.99%.

How severe is CVE-2026-26278?

CVE-2026-26278 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.99% probability of exploitation.

Which products are affected by CVE-2026-26278?

Affected products include Naturalintelligence Fast-xml-parser.

How do I fix CVE-2026-26278?

Upgrade affected software to a fixed version, for example Naturalintelligence Fast-xml-parser 5.3.6 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-26278 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.