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

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Summary

CVECVE-2026-33979
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-27 22:16:22 UTC
Updated2026-03-31 18:24:58 UTC
DescriptionExpress 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.

Risk And Classification

Primary CVSS: v3.1 8.2 HIGH from [email protected]

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

EPSS: 0.000100000 probability, percentile 0.010110000 (date 2026-04-01)

Problem Types: CWE-79 | CWE-183 | CWE-183 CWE-183: Permissive List of Allowed Inputs | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
3.1CNADECLARED8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
None

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Express Xss Sanitizer Project Express Xss Sanitizer All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA AhmedAdelFahim Express-xss-sanitizer affected < 2.0.2 Not specified

References

ReferenceSourceLinkTags
github.com/AhmedAdelFahim/express-xss-sanitizer/commit/5623009ef11dcf095... [email protected] github.com Patch
github.com/AhmedAdelFahim/express-xss-sanitizer/releases/tag/v2.0.2 [email protected] github.com Product, Release Notes
github.com/AhmedAdelFahim/express-xss-sanitizer/security/advisories/GHSA... [email protected] github.com Exploit, Mitigation, Vendor Advisory
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