CVE-2026-65903: Dompurify DOMPurify's ADD_TAGS Function Form Bypasses Vulnerability

MODERATE
Advisory Identifier: GHSA-39q2-94rc-95cp
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CWE-783
Published
Advisory Summary

CVE-2026-65903 is a MODERATE dompurify's add_tags function form bypasses vulnerability (CWE-783: Operator Precedence Logic Error) affecting Dompurify libraries in the npm ecosystem. The issue involves dompurify's add_tags function form bypasses forbid_tags due to short-circuit evaluation. Remediation is available by upgrading affected packages to version 3.4.0.

CVE-2026-65903 at a Glance

CVE Identifier CVE-2026-65903
GHSA Identifier GHSA-39q2-94rc-95cp
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-783: Operator Precedence Logic Error
Affected Product Dompurify
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-65903

To remediate this vulnerability, upgrade all affected Dompurify dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

dompurify fixed: 3.4.0 
npm install dompurify@3.4.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls dompurify

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-65903, inspect your project dependencies using npm:

npm ls dompurify

Analyze the terminal output to locate any version of Dompurify in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.4.0), your application is affected.

Note: The npm ls dompurify command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-783: Operator Precedence Logic Error, where the product uses an expression in which operator precedence causes incorrect logic to be used. In Dompurify, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Summary In `src/purify.ts:1117-1123`, `ADD_TAGS` as a function (via `EXTRA_ELEMENT_HANDLING.tagCheck`) bypasses `FORBID_TAGS` due to short-circuit evaluation. The condition: ``` !(tagCheck(tagName)) && (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName]) ``` When `tagCheck(tagName)` returns `true`, the entire condition is `false` and the element is kept — `FORBID_TAGS[tagName]` is never evaluated. ## Inconsistency This contradicts the attribute-side pattern at line 1214 where `FORBID_ATTR` explicitly wins first: ``` if (FORBID_ATTR[lcName]) { continue; } ``` For tags, FORBID should also take precedence over ADD. ## Impact Applications using both `ADD_TAGS` as a function and `FORBID_TAGS` simultaneously get unexpected behavior — forbidden tags are allowed through. Config-dependent but a genuine logic inconsistency. ## Suggested Fix Check `FORBID_TAGS` before `tagCheck`: ``` if (FORBID_TAGS[tagName]) { /* remove */ } else if (tagCheck(tagName) || ALLOWED_TAGS[tagName]) { /* keep */ } ``` ## Affected Version v3.3.3 (commit 883ac15)

CVE-2026-65903 Affected Dompurify Versions

1 component(s)
Fixed Versions:
3.4.0
Product / Package Ecosystem Affected Versions Fixed Version
dompurify
npm/dompurify
npm
< 3.4.0
3.4.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/cure53/DOMPurify/security/advisories/GHSA-39q2-94rc-95cp
Dompurify Source Repository REPOSITORY
https://github.com/cure53/DOMPurify

Frequently Asked Questions

What is CVE-2026-65903?
CVE-2026-65903 is a security vulnerability in Dompurify involving DOMPurify's ADD_TAGS function form bypasses FORBID_TAGS due to short-circuit evaluation under CWE-783: Operator Precedence Logic Error.
Which Dompurify versions are affected?
Affected versions include releases prior to 3.4.0 across affected packages: dompurify.
What version fixes CVE-2026-65903?
Upgrading to 3.4.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is dompurify affected?
Yes, dompurify is affected in releases prior to 3.4.0. Upgrade your dependency to 3.4.0 or later.
What CWE is associated with CVE-2026-65903?
CVE-2026-65903 is classified under CWE-783: Operator Precedence Logic Error (The product uses an expression in which operator precedence causes incorrect logic to be used.).
How can I check npm dependencies for CVE-2026-65903?
Run the dependency tree command: 'npm ls dompurify'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-39q2-94rc-95cp",
  "modified" : "2026-07-23T14:01:46Z",
  "published" : "2026-04-16T00:46:35Z",
  "aliases" : [ "CVE-2026-65903" ],
  "summary" : "DOMPurify's ADD_TAGS function form bypasses FORBID_TAGS due to short-circuit evaluation",
  "details" : "## Summary\nIn `src/purify.ts:1117-1123`, `ADD_TAGS` as a function (via `EXTRA_ELEMENT_HANDLING.tagCheck`) bypasses `FORBID_TAGS` due to short-circuit evaluation.\n\nThe condition:\n```\n!(tagCheck(tagName)) && (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName])\n```\nWhen `tagCheck(tagName)` returns `true`, the entire condition is `false` and the element is kept — `FORBID_TAGS[tagName]` is never evaluated.\n\n## Inconsistency\nThis contradicts the attribute-side pattern at line 1214 where `FORBID_ATTR` explicitly wins first:\n```\nif (FORBID_ATTR[lcName]) { continue; }\n```\nFor tags, FORBID should also take precedence over ADD.\n\n## Impact\nApplications using both `ADD_TAGS` as a function and `FORBID_TAGS` simultaneously get unexpected behavior — forbidden tags are allowed through. Config-dependent but a genuine logic inconsistency.\n\n## Suggested Fix\nCheck `FORBID_TAGS` before `tagCheck`:\n```\nif (FORBID_TAGS[tagName]) { /* remove */ }\nelse if (tagCheck(tagName) || ALLOWED_TAGS[tagName]) { /* keep */ }\n```\n\n## Affected Version\nv3.3.3 (commit 883ac15)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "dompurify"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.4.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.3.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/cure53/DOMPurify/security/advisories/GHSA-39q2-94rc-95cp"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cure53/DOMPurify"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-783" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-16T00:46:35Z",
    "nvd_published_at" : null
  }
}