CVE-2026-42052: Beets Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3gxm-wfjx-m847",
  "modified" : "2026-06-24T00:30:30Z",
  "published" : "2026-04-29T18:29:00Z",
  "aliases" : [ "CVE-2026-42052" ],
  "summary" : "beets has a Cross-site Scripting vulnerability",
  "details" : "During code logic analyis, an area that may lead to unintended behavior under specific conditions was discovered. \n\n## Overview\n- Verified Version: `80cd21554124da07d17a4f962c7d770a4f70d0f2`\n- Vulnerability Type: Stored XSS\n- Affected Location: `beetsplug/web/templates/index.html:42`\n- Trigger Scenario: Metadata fields such as `title`, `lyrics`, or `comments` are rendered with raw template interpolation and inserted into DOM via `.html(...)`.\n\n## Root Cause\nThe bundled web UI uses Underscore template interpolation mode `<%= ... %>` for untrusted metadata fields. In this runtime, `<%= ... %>` is raw insertion and HTML escaping is only performed by `<%- ... %>`. Rendered output is then inserted with `.html(...)`, allowing attacker-controlled markup to become active DOM.\n\n## Source-to-Sink Chain\n1. Source (attacker-controlled input)\n- Item metadata values (for example `title`, `lyrics`, `comments`) can contain attacker HTML payload.\n\n2. Data flow\n- Templates in `beetsplug/web/templates/index.html:42-46,87-91` render metadata with `<%= ... %>`.\n- Underscore runtime defines `<%= ... %>` as raw interpolation (`beetsplug/web/static/underscore.js:890-907`).\n\n3. Sink (security-sensitive action)\n- Frontend inserts rendered template output into DOM via `$(this.el).html(this.template(this.model.toJSON()));` in `beetsplug/web/static/beets.js:182,208,220`.\n\n## Exploitation Preconditions\n1. Victim opens the web UI page that renders attacker-controlled metadata.\n2. Metadata includes executable HTML/JS payload.\n\n## Risk\nStored payload executes in the web UI context and can perform actions available to that origin.\n\n## Impact\nAttacker can run arbitrary JavaScript in the victim browser, exfiltrate viewable data, and perform UI-driven actions as the victim session.\n\n## Remediation\n1. Replace raw interpolation `<%= ... %>` with escaped output `<%- ... %>` for untrusted fields.\n2. Avoid `.html(...)` for untrusted template output; use text-safe rendering.\n3. Sanitize metadata values on ingest and before rendering, including attribute contexts.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "beets"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.10.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/beetbox/beets/security/advisories/GHSA-3gxm-wfjx-m847"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42052"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/beetbox/beets"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/beetbox/beets/releases/tag/v2.10.0"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2026/06/msg00030.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-29T18:29:00Z",
    "nvd_published_at" : "2026-05-04T18:16:30Z"
  }
}