Vulnerability in justhtml (CVE-2026-7808)
Summary
Vulnerability in justhtml (CVE-2026-7808). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 1.16.0 or later.
Original description
The description as published by the source.
Summary
justhtml 1.16.0 fixes multiple security issues in sanitization, serialization, and programmatic DOM handling.
Most of these issues affected one of these advanced paths rather than ordinary parsed HTML with the default safe settings:
- programmatic DOM input to
sanitize()orsanitize_dom() - reused or mutated sanitization policy objects
- custom policies that preserve foreign namespaces such as SVG or MathML
Affected versions
justhtml<= 1.15.0
Fixed version
justhtml1.16.0released on April 12, 2026
Impact
Policy reuse and mutation
Nested mutation of sanitization policy internals could weaken later sanitization by leaving stale compiled sanitizers active, or by mutating exported default policy internals process-wide.
In-memory sanitization gaps
Programmatic DOM sanitization could miss dangerous mixed-case tag names such as ScRiPt or StYlE, and custom drop_content_tags values such as {"SCRIPT"} could silently fail to drop dangerous subtrees.
Serialization injection
Crafted programmatic doctype names could serialize into active markup before the document body.
Foreign-namespace policy bypasses
Custom policies that preserve SVG or MathML could allow active SVG features to survive sanitization, including:
- animation elements such as
andthat mutate already-sanitized attributes after sanitization - presentation attributes such as
fill,clip-path,mask,marker-start, andcursorcontaining…
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-2026-7808 has been found in justhtml.
Successful exploitation can lead to full system takeover. CVSS score: 9.8/10.
What to do: upgrade justhtml to 1.16.0 or later.
If unsure, ask your IT team or search "justhtml CVE-2026-7808" on the vendor's site.
CVE-2026-7808 (justhtml) — CWE-20 / CVSS v3 9.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 1.16.0 — 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.
A vulnerability (CWE-20) exists in justhtml.
Check the vendor advisory for the affected versions of justhtml.
Severity: Critical (CVSS 9.8/10). Successful exploitation can lead to full system takeover.
Update to 1.16.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'justhtml' . 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
-
1Identify exposure identify
grep -r 'justhtml' . | 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
justhtmlを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade justhtml to 1.16.0ステージング環境で 1.16.0 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。
-
3Post-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
References
- package github.com
- web github.com
- web disclosure@vulncheck.com
- web nvd.nist.gov
- web github.com