How severe is CVE-2026-33979?

CVE-2026-33979 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity high, and availability none.

Is CVE-2026-33979 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (30th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33979?

CVE-2026-33979 affects Express Xss Sanitizer Project Express Xss Sanitizer. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33979?

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-2026-33979 have an EU (EUVD) identifier?

Yes. CVE-2026-33979 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16876.

When was CVE-2026-33979 published?

CVE-2026-33979 was published on 2026-03-27 and last updated on 2026-06-17.

CVE-2026-33979

CVE-2026-33979 is a high-severity vulnerability in Express Xss Sanitizer Project Express Xss Sanitizer with a CVSS 3.x base score of 8.2. 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-79.

Key facts

Severity: High (CVSS 3.x base score 8.2)
EPSS exploit prediction: 0% (30th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16876
Weakness: CWE-79
Affected product: Express Xss Sanitizer Project Express Xss Sanitizer
Published: 2026-03-27
Last modified: 2026-06-17

Description

Express XSS Sanitizer is Express 4.x and 5.x middleware which sanitizes user input data (in req.body, req.query, req.headers and req.params) to prevent Cross Site Scripting (XSS) attack. A vulnerability has been identified in versions prior to 2.0.2 where restrictive sanitization configurations are silently ignored. In version 2.0.2, the validation logic has been updated to respect explicitly provided empty configurations. Now, if allowedTags or allowedAttributes are provided (even if empty), they are passed directly to sanitize-html without being overridden.

Frequently asked questions

What is CVE-2026-33979?: Express XSS Sanitizer is Express 4.x and 5.x middleware which sanitizes user input data (in req.body, req.query, req.headers and req.params) to prevent Cross Site Scripting (XSS) attack. A vulnerability has been identified in versions prior to 2.0.2 where restrictive sanitization configurations are silently ignored. In version 2.0.2, the validation logic has been updated to respect explicitly provided empty configurations. Now, if allowedTags or allowedAttributes are provided (even if empty), they are passed directly to sanitize-html without being overridden.
How severe is CVE-2026-33979?: CVE-2026-33979 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity high, and availability none.
Is CVE-2026-33979 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (30th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33979?: CVE-2026-33979 affects Express Xss Sanitizer Project Express Xss Sanitizer. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33979?: 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-2026-33979 have an EU (EUVD) identifier?: Yes. CVE-2026-33979 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16876.
When was CVE-2026-33979 published?: CVE-2026-33979 was published on 2026-03-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:express_xss_sanitizer_project:express_xss_sanitizer:*:*:*:*:*:node.js:*:*

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