CVE-2026-68537 is a high-severity (CVSS 7.5) vulnerability in fulgur. A fix is available for fulgur — see the affected versions and patch details below.
Fulgur: Non-painting replaced elements amplify to thousands of blank PDF pages (denial of service)
Real-World Exposure
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Description
fulgur 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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | fulgur | all versions | 0.26.0cargo update -p fulgur --precise 0.26.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fulgur, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fulgur to 0.26.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-68537 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-68537 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-68537. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-68537 in your dependencies?
O3 Security finds CVE-2026-68537 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.