Summary
Fulgur: Non-painting replaced elements amplify to thousands of blank PDF pages (denial of service)
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.
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
Impact
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-68537 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.26.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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.
Frequently Asked Questions
- What is CVE-2026-68537? CVE-2026-68537 is a high-severity uncontrolled resource consumption vulnerability in fulgur (rust), affecting versions < 0.26.0. It is fixed in 0.26.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-68537? CVE-2026-68537 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of fulgur are affected by CVE-2026-68537? fulgur (rust) versions < 0.26.0 is affected.
- Is there a fix for CVE-2026-68537? Yes. CVE-2026-68537 is fixed in 0.26.0. Upgrade to this version or later.
- Is CVE-2026-68537 exploitable, and should I be worried? Whether CVE-2026-68537 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-68537 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-68537? Upgrade
fulgurto 0.26.0 or later.