GHSA-4RF6-QX84-Q9FV
Vulnerability from github – Published: 2026-09-17 18:49 – Updated: 2026-09-17 18:49fulgur converts untrusted HTML/CSS into PDF, commonly on a server that
processes input supplied by many tenants. In versions prior to 0.26.0, a
childless box that resolves to a pathologically tall height was amplified into
thousands of blank PDF pages, even when it produces no visible output.
The childless-collapse defense that would normally collapse such a box was gated by a tag-only "replaced content" check, so any non-painting replaced element bypassed it, including:
- an unresolved
src(the common offline-first case), - a
visibility:hiddenimage, - an undecodable image format, and
- an empty
<svg>.
A trailing-sibling variant of the same gap was also open. A few bytes of HTML
therefore amplified into roughly MAX_PAGES (10,000) blank pages; the renderer
allocates and runs a per-page loop over them, producing CPU and memory
exhaustion. An attacker able to submit HTML to a fulgur-based conversion service
can trigger this with a trivially small payload, denying service to the host and
any co-tenants.
Patches
Fixed in 0.26.0 (PR #575). The tag-only gate was removed so that any
pathologically tall childless box collapses regardless of whether it is a
replaced element, closing the missing-src, visibility:hidden,
undecodable-format, and empty-<svg> vectors at once, along with the
trailing-sibling variant.
Workarounds
Upgrade to 0.26.0 or later. If upgrading is not immediately possible, validate
or constrain untrusted CSS (in particular very large height / vh on
elements) before passing HTML to fulgur.
Related
Versions prior to 0.19.0 additionally lacked any page-count cap, allowing an unbounded (rather than 10,000-page) variant of this amplification and a non-terminating loop on non-finite heights. That earlier variant is tracked separately as GHSA-j5cx-ph8g-95v3.
Attack Vector rationale
fulgur performs no network I/O of its own; it renders HTML/CSS handed to it by
the embedding application. This advisory scores the crate independent of any
specific adopting program, so per the CVSS v3.1 User Guide §3.7 (scoring library
vulnerabilities related to incoming data) the Attack Vector is assessed as
Network for the reasonable worst-case deployment — a network-facing service
that renders untrusted, attacker-supplied HTML without user interaction. A
concrete system that receives the HTML in one component and passes it to fulgur
in a separate component may assess a lower environmental Attack Vector (Local,
per §3.10).
References
- Fix: https://github.com/fulgur-rs/fulgur/pull/575
{
"affected": [
{
"package": {
"ecosystem": "crates.io",
"name": "fulgur"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.26.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-68537"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-17T18:49:15Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"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 `\u003csvg\u003e`.\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-`\u003csvg\u003e` 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 \u00a73.7 (scoring library\nvulnerabilities related to incoming data) the Attack Vector is assessed as\n**Network** for the reasonable worst-case deployment \u2014 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 \u00a73.10).\n\n## References\n\n- Fix: https://github.com/fulgur-rs/fulgur/pull/575",
"id": "GHSA-4rf6-qx84-q9fv",
"modified": "2026-09-17T18:49:15Z",
"published": "2026-09-17T18:49:15Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "Fulgur: Non-painting replaced elements amplify to thousands of blank PDF pages (denial of service)"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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