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CVE-2026-44898

Estado: AnalizadaMedia (6.1)—

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a <ul> table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#<id>") and the text value (used as the visible link label) are inserted into <a> tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Mistune Project — Mistune

CWE

Referencias

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{
  "id": "CVE-2026-44898",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44898",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-05-27T17:57:34.250055Z"
        }
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    ],
    "cvssMetricV31": [
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        "cvssData": {
          "scope": "CHANGED",
          "version": "3.1",
          "baseScore": 6.1,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 2.7,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
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      "source": "security-advisories@github.com",
      "affectedData": [
        {
          "vendor": "lepture",
          "product": "mistune",
          "versions": [
            {
              "status": "affected",
              "version": "< 3.2.1"
            }
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        }
      ]
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  ],
  "published": "2026-05-26T21:16:39.810",
  "references": [
    {
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1",
      "tags": [
        "Product",
        "Release Notes"
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      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
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  "weaknesses": [
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      "source": "security-advisories@github.com",
      "description": [
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          "value": "CWE-79"
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a <ul> table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href=\"#<id>\") and the text value (used as the visible link label) are inserted into <a> tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href=\"#...\" attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1."
    },
    {
      "lang": "es",
      "value": "Mistune es un analizador de Markdown para Python con renderizadores y complementos. Antes de la versión 3.2.1, render_toc_ul() construye un árbol <ul> de tabla de contenidos a partir de una lista de tuplas (nivel, id, texto). Tanto el valor de 'id' (usado como href='#<id>') como el valor de 'text' (usado como la etiqueta visible del enlace) se insertan en etiquetas <a> a través de una cadena de formato de Python simple - sin aplicar escape HTML a ninguno de los valores. Cuando los IDs de los encabezados se derivan del texto de encabezado proporcionado por el usuario (el caso de uso estándar para anclas de slug legibles), un atacante puede crear un encabezado cuyo texto rompe el contexto del atributo href='#...', inyectando etiquetas HTML arbitrarias, incluidos bloques <script>, directamente en la tabla de contenidos renderizada. Esta vulnerabilidad se corrige en la versión 3.2.1."
    }
  ],
  "lastModified": "2026-07-24T11:10:00.170",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "criteria": "cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*",
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  "sourceIdentifier": "security-advisories@github.com"
}