TI-2026-26320 Aliases CVE-2026-33979 GHSA-3843-rr4g-m8jq

Express XSS Sanitizer: allowedTags/allowedAttributes bypass leads to permissive sanitization (XSS risk)

HIGH 75CWE-183Published 2026-03-27 · Updated 2026-03-31

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Cross-site scripting
Confidentiality · integrity · availability: Low · High · None
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00389 33rd percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Fixed express-xss-sanitizer (AhmedAdelFahim): 2.0.2express-xss-sanitizer (npm): 2.0.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
AhmedAdelFahim	express-xss-sanitizer	before 2.0.2	2.0.2	Patch available	CNA
—	express-xss-sanitizer (npm)	before 2.0.2	2.0.2	Patch available	GHSA-3843-rr4g-m8jq

express-xss-sanitizer VendorAhmedAdelFahim Affected before 2.0.2 Fixed in 2.0.2 Patch available CNA
express-xss-sanitizer (npm) Vendor— Affected before 2.0.2 Fixed in 2.0.2 Patch available GHSA-3843-rr4g-m8jq

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:express_xss_sanitizer_project:express_xss_sanitizer::::::node.js::*	before 2.0.2	Vulnerable	Express XSS Sanitizer project

cpe:2.3:a:express_xss_sanitizer_project:express_xss_sanitizer:*:*:*:*:*:node.js:*:* Versions before 2.0.2 Vulnerable ·Express XSS Sanitizer project

Remediation

Fix · CNA express-xss-sanitizer (AhmedAdelFahim) Fixed in 2.0.2
Fix · GHSA-3843-rr4g-m8jq express-xss-sanitizer (npm) Fixed in 2.0.2 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-33979
2026-10-03 Alias added: GHSA-3843-rr4g-m8jq

References

Other 2

TI-2022-05570 Prototype pollution in express-xss-sanitizer CVSS 3.1HIGH 7.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences