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CVE-2026-63670 medium CVSS 6.1

Cross-Site Scripting (XSS) in sanitize-html (CVE-2026-63670)

Summary

Cross-site scripting in sanitize-html (CVE-2026-63670). Risk of unauthorized operations or information disclosure. Exploitable via textarea. Mitigation: upgrade to 2.17.6 or later.

Original description

The description as published by the source.

Summary

A mutation-XSS / allowedTags bypass: when textarea (or xmp) is included in allowedTags, an input containing a literal (a solidus right after the RCDATA end-tag name) lets non-allowed markup such as pass through sanitizeHtml() live and unescaped, even though img/onerror are not in the allowlist. A spec-compliant browser executes the surviving handler — XSS. This is a literal-solidus variant that bypasses the two most recent fixes in this code area (CVE-2026-40186, CVE-2026-44990), both already applied in 2.17.5. The default configuration is not affected.

Details

sanitize-html emits the text content of HTML raw-text elements (textarea, xmp) without escaping. Two things combine:

  • Parser differential: on input, htmlparser2 does NOT recognize (solidus after the RCDATA end-tag name) as a close tag; it emits as a single raw-text node.
  • Unescaped passthrough: the ontext handler (index.js ~575-583) appends textarea/xmp content with
    result += text (no escapeHtml), assuming it is "already properly encoded" — true for entity-decoded
    content (what CVE-2026-40186 fixed) but false for this mis-tokenized literal close tag.
    A spec browser treats as a valid `textarea` close, so the following is parsed as a live element. The recent fixes addressed entity-encoding (CVE-2026-40186) and the xmp default (CVE-2026-44990); neither covers the literal-solidus mis-tokenization, so the raw passthrough still leaks.

P…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-63670 has been found in sanitize-html.
Attackers can target a specific entry point like textarea over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade sanitize-html to 2.17.6 or later.
If unsure, ask your IT team or search "sanitize-html CVE-2026-63670" on the vendor's site.

CVE-2026-63670 (sanitize-html) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: textarea / xmp / allowedTags / img
Patched: 2.17.6 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in sanitize-html. Attackers reach the vulnerable code path via textarea without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of sanitize-html. Attack surface: textarea / xmp / allowedTags / img.

🔥 Severity

Severity: Medium (CVSS 6.1/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.17.6.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'sanitize-html' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'sanitize-html' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で sanitize-html を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade sanitize-html to 2.17.6

    ステージング環境で 2.17.6 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm sanitize-html
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.17.6"}]}]

References

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