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CVE-2026-44708 medium CVSS 6.1

Cross-Site Scripting (XSS) in mistune (CVE-2026-44708)

Summary

Cross-site scripting in mistune (CVE-2026-44708). Risk of unauthorized operations or information disclosure. Exploitable via _escape.

Original description

The description as published by the source.

Summary

The mistune math plugin renders inline math ($...$) and block math ($$...$$) by concatenating the raw user-supplied content directly into the HTML output without any HTML escaping. This occurs even when the parser is explicitly created with escape=True, which is supposed to guarantee that all user-controlled text is sanitised before reaching the DOM.

The result is a silent contract violation: a developer who enables escape=True reasonably expects complete XSS protection, but the math plugin operates as an independent render path that ignores the renderer's _escape flag entirely.

Details

File: src/mistune/plugins/math.py

def render_inline_math(renderer, text):
    # `text` is raw user input — no escape() call anywhere
    return r'\(' + text + r"\)"

def render_block_math(renderer, text):
    # same issue for block-level $$...$$
    return '$$\n' + text + "\n$$\n"

Both functions take text directly from the parsed token and concatenate it into the output string. Neither function:

  • calls escape(text) from mistune.util
  • checks renderer._escape
  • calls safe_entity(text) or any other sanitisation helper

The escape=True flag only influences the main HTMLRenderer methods (paragraph, heading, codespan, etc.). Plugin render functions registered via md.renderer.register() receive the renderer instance but have no mechanism that enforces the escape contract - they must opt in manually, and math.py does not.…

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-2026-44708 has been found in mistune.
Attackers can target a specific entry point like _escape over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "mistune CVE-2026-44708" on the vendor's site.

CVE-2026-44708 (mistune) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: _escape / text / mistune.util / renderer._escape
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 _escape without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of mistune. Attack surface: _escape / text / mistune.util / renderer._escape.

🔥 Severity

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

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ 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
    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"}]}]
PyPI mistune
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"3.2.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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