CVE-2022-21169Public exploitNetwork attack vector

XSS bypass via inherited allowedTags option

Published Sep 26, 2022 · Updated May 21, 2025

Prototype pollution in express-xss-sanitizer before 1.1.3 allows remote attackers to bypass XSS sanitization via allowedTags. The initializeOptions function in lib/sanitize.js reads inherited allowedTags and allowedKeys properties and passes an inherited tag allowlist to sanitize-html. Exploitation requires the application's Object prototype to be polluted first; attacker-controlled script tags can then survive sanitization and execute when rendered for a user.

CVSS severity6.1
Medium
EPSS probability0.79%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Prototype pollution in express-xss-sanitizer before 1.1.3 allows remote attackers to bypass XSS sanitization via allowedTags. The initializeOptions function in lib/sanitize.js reads inherited allowedTags and allowedKeys properties and passes an inherited tag allowlist to sanitize-html. Exploitation requires the application's Object prototype to be polluted first; attacker-controlled script tags can then survive sanitization and execute when rendered for a user.

The record

CVE
CVE-2022-21169
Published
Sep 26, 2022
Updated
May 21, 2025
Vendor
Express XSS Sanitizer project
Product
express-xss-sanitizer
Classifications
CWE-1321, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 26, 2022CVE publishedPublication date reported by the CVE source.
  2. May 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <1.1.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Express XSS Sanitizer project · express-xss-sanitizerversion=unspecified <1.1.3

Published CVSS scores

7.3SnykCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
6.1NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
T1059.007JavaScript/JScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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