CVE-2026-68537: Fulgur Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4rf6-qx84-q9fv",
  "modified" : "2026-09-17T18:49:15Z",
  "published" : "2026-09-17T18:49:15Z",
  "aliases" : [ "CVE-2026-68537" ],
  "summary" : "Fulgur: Non-painting replaced elements amplify to thousands of blank PDF pages (denial of service)",
  "details" : "`fulgur` converts untrusted HTML/CSS into PDF, commonly on a server that\nprocesses input supplied by many tenants. In versions prior to 0.26.0, a\nchildless box that resolves to a pathologically tall height was amplified into\nthousands of blank PDF pages, even when it produces no visible output.\n\nThe childless-collapse defense that would normally collapse such a box was gated\nby a tag-only \"replaced content\" check, so any **non-painting replaced element**\nbypassed it, including:\n\n- an unresolved `src` (the common offline-first case),\n- a `visibility:hidden` image,\n- an undecodable image format, and\n- an empty `<svg>`.\n\nA trailing-sibling variant of the same gap was also open. A few bytes of HTML\ntherefore amplified into roughly `MAX_PAGES` (10,000) blank pages; the renderer\nallocates and runs a per-page loop over them, producing CPU and memory\nexhaustion. An attacker able to submit HTML to a fulgur-based conversion service\ncan trigger this with a trivially small payload, denying service to the host and\nany co-tenants.\n\n## Patches\n\nFixed in **0.26.0** (PR #575). The tag-only gate was removed so that any\npathologically tall childless box collapses regardless of whether it is a\nreplaced element, closing the missing-`src`, `visibility:hidden`,\nundecodable-format, and empty-`<svg>` vectors at once, along with the\ntrailing-sibling variant.\n\n## Workarounds\n\nUpgrade to 0.26.0 or later. If upgrading is not immediately possible, validate\nor constrain untrusted CSS (in particular very large `height` / `vh` on\nelements) before passing HTML to fulgur.\n\n## Related\n\nVersions prior to 0.19.0 additionally lacked any page-count cap, allowing an\nunbounded (rather than 10,000-page) variant of this amplification and a\nnon-terminating loop on non-finite heights. That earlier variant is tracked\nseparately as GHSA-j5cx-ph8g-95v3.\n\n## Attack Vector rationale\n\n`fulgur` performs no network I/O of its own; it renders HTML/CSS handed to it by\nthe embedding application. This advisory scores the crate independent of any\nspecific adopting program, so per the CVSS v3.1 User Guide §3.7 (scoring library\nvulnerabilities related to incoming data) the Attack Vector is assessed as\n**Network** for the reasonable worst-case deployment — a network-facing service\nthat renders untrusted, attacker-supplied HTML without user interaction. A\nconcrete system that receives the HTML in one component and passes it to fulgur\nin a separate component may assess a lower environmental Attack Vector (Local,\nper §3.10).\n\n## References\n\n- Fix: https://github.com/fulgur-rs/fulgur/pull/575",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "fulgur"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.26.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fulgur-rs/fulgur/security/advisories/GHSA-4rf6-qx84-q9fv"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fulgur-rs/fulgur/pull/575"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fulgur-rs/fulgur"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2026-0201.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-17T18:49:15Z",
    "nvd_published_at" : null
  }
}