CVE-2026-26278

CVE-2026-26278 is a high-severity vulnerability in Naturalintelligence Fast-xml-parser with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-776.

Key facts

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.

Frequently asked questions

What is CVE-2026-26278?
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.
How severe is CVE-2026-26278?
CVE-2026-26278 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-26278 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-26278?
CVE-2026-26278 affects Naturalintelligence Fast-xml-parser. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-26278?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-26278 have an EU (EUVD) identifier?
Yes. CVE-2026-26278 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7970.
When was CVE-2026-26278 published?
CVE-2026-26278 was published on 2026-02-19 and last updated on 2026-06-30.

References

Affected products (1)

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