Sign in Sign up
JA · EN · FR
SecPulse
Categories
CVE-2026-44897 medium CVSS 6.1

Cross-Site Scripting (XSS) in mistune (CVE-2026-44897)

Summary

Cross-site scripting in mistune (CVE-2026-44897). Risk of unauthorized operations or information disclosure. Exploitable via toc_1. Mitigation: upgrade to 3.2.1 or later.

Original description

The description as published by the source.

Summary

HTMLRenderer.heading() builds the opening `` tag by string-concatenating the id attribute value directly into the HTML — with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character " in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element.

The default TOC hook assigns safe auto-incremented IDs (toc_1, toc_2, …) that never contain user text. However, the add_toc_hook() API accepts a caller-supplied heading_id callback. Deriving heading IDs from the heading text itself — to produce human-readable slug anchors like #installation or #getting-started — is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the id= attribute.

Details

File: src/mistune/renderers/html.py

def heading(self, text: str, level: int, **attrs: Any) -> str:
    tag = "h" + str(level)
    html = "<" + tag
    _id = attrs.get("id")
    if _id:
        html += ' id="' + _id + '"'    # ← _id is never escaped
    return html + ">" + text + "</" + tag + ">\n"

The text body (line content) is escaped upstream by the inline token renderer, which is why text arrives as &quot; etc. But _id arrives as a raw string directly from whatever the…

Source: GitHub Security Advisories (Global) 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-2026-44897 has been found in mistune.
Attackers can target a specific entry point like toc_1 over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade mistune to 3.2.1 or later.
If unsure, ask your IT team or search "mistune CVE-2026-44897" on the vendor's site.

CVE-2026-44897 (mistune) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: toc_1 / toc_2 / heading_id / text
Patched: 3.2.1 — 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 mistune. Attackers reach the vulnerable code path via toc_1 without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of mistune. Attack surface: toc_1 / toc_2 / heading_id / text.

🔥 Severity

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

🔧 How to fix

Update to 3.2.1.

🛡️ 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 'mistune' . 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 'mistune' . | 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 mistune 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 mistune to 3.2.1

    ステージング環境で 3.2.1 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

pip mistune
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.2.1"}]}]
PyPI mistune
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.2.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

We use cookies for analytics and ad measurement. This setting applies to all Game co., Ltd. sites. Details