Skip to content
Patch Next
Sign inAdd to your agent

← Actionable
High, CVSS 8.2amended

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

CVE-2026-33979GHSA-3843-rr4g-m8jq

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (express-xss-sanitizer 2.0.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

Add to your agent

Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
EPSS
  • CVE-2026-33979: 0.39% estimated exploitation activity in the next 30 days; percentile 33.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Description A vulnerability has been identified in express-xss-sanitizer (<= 2.0.1) where restrictive sanitization configurations are silently ignored. When a developer explicitly sets: allowedTags: [] allowedAttributes: {} the library incorrectly treats these values as "not provided" due to length/emptiness checks, and falls back to sanitize-html's default configuration. As a result, instead of stripping all HTML tags and attributes, the sanitizer allows a permissive set of tags . This behavior violates the expected API contract and may lead to security issues such as content injection or XSS, depending on how the sanitized output is used. Impact Developers intending to fully strip HTML content by providing empty allowedTags or allowedAttributes configurations may unknowingly allow a wide range of HTML elements and attributes. This can result in: - Injection of unintended HTML content - Injection of links via - Potential XSS vectors depending on downstream usage The impact depends…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-3843-rr4g-m8jq

  2. Revision 1 · created ·

    Published from osv record GHSA-3843-rr4g-m8jq

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-33979

Advisory: Express XSS Sanitizer: allowedTags/allowedAttributes bypass leads to permissive sanitization (XSS risk)
IDs: CVE-2026-33979, GHSA-3843-rr4g-m8jq
Record: https://patchnext.com/advisories/cve-2026-33979 (revision 2, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: express-xss-sanitizer 2.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm express-xss-sanitizer: affected < 2.0.2; fixed in 2.0.2

## Suggested inspection (read-only)
- `npm ls express-xss-sanitizer --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on express-xss-sanitizer.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3843-rr4g-m8jq (OSV record GHSA-3843-rr4g-m8jq lists affected ranges: npm express-xss-sanitizer >=0 <2.0.2 (fixed))
- Verified: https://github.com/advisories/GHSA-3843-rr4g-m8jq (GitHub-reviewed advisory GHSA-3843-rr4g-m8jq lists affected ranges: npm express-xss-sanitizer >=0 <2.0.2)

Commands are suggestions: review each one before running it.

Loading voting…