XSS in Ahmedadelfahim Express-Xss-Sanitizer
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N.
EPSS exploit prediction
EPSS: 0.004 (35.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- Ahmedadelfahim Express-Xss-Sanitizer — versions < 2.0.2
- Express Xss Sanitizer Project
Weakness classification (CWE)
References
- github.com/AhmedAdelFahim/express-xss-sanitizer/security/advisories/GHSA-3843-r… (Exploit, Mitigation, Vendor Advisory)
- github.com/AhmedAdelFahim/express-xss-sanitizer/commit/5623009ef11dcf095c163a38… (Patch)
- github.com/AhmedAdelFahim/express-xss-sanitizer/releases/tag/v2.0.2 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-33979?
- CVE-2026-33979 is a high-severity vulnerability in Ahmedadelfahim Express-Xss-Sanitizer, classified under Cross-site Scripting. CVSS score: 8.2/10. Published 2026-03-27.
- How severe is CVE-2026-33979?
- High severity. CVSS v3 base score is 8.2 out of 10.