CVE-2026-27469: Isso Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9fww-8cpr-q66r",
  "modified" : "2026-02-24T16:03:04Z",
  "published" : "2026-02-24T16:03:04Z",
  "aliases" : [ "CVE-2026-27469" ],
  "summary" : "Isso affected by Stored XSS via comment website field",
  "details" : "## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/<id>) and the moderation edit endpoint (POST /id/<id>/edit/<key>).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/<id>, POST /id/<id>/edit/<key>), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape — note the quote parameter",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "isso"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.13.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27469"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"
  }, {
    "type" : "WEB",
    "url" : "https://docs.python.org/3/library/html.html#html.escape"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/isso-comments/isso"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116", "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-24T16:03:04Z",
    "nvd_published_at" : "2026-02-21T08:16:11Z"
  }
}