- Reported
-
- Issued
-
- Package
-
fulgur
(crates.io)
- Type
-
Vulnerability
- Categories
-
- Keywords
-
#dos
#pagination
#pdf
- Aliases
-
- References
-
- CVSS Score
- 7.5
HIGH
- CVSS Details
-
- Attack Vector
- Network
- Attack Complexity
- Low
- Privileges Required
- None
- User Interaction
- None
- Scope
- Unchanged
- Confidentiality Impact
- None
- Integrity Impact
- None
- Availability Impact
- High
- CVSS Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Patched
-
Description
fulgur converts untrusted HTML/CSS into PDF, commonly on a server that
processes input supplied by many tenants. In versions prior to 0.19.0, a
body-direct child whose CSS-resolved height greatly exceeds the page height was
sliced into one fragment per page with no upper bound.
The height is taken directly from attacker-controlled HTML/CSS (height, vh
units), so a few bytes such as <div style="height:99999999px"></div> forced on
the order of 125,000 page fragments. The pagination code then allocates
vec![Vec::new(); page_count] and runs a per-page render loop, resulting in CPU
and memory exhaustion. A non-finite height (one that resolves to +inf)
additionally made the slicing loop's remaining -= last_slice_h decrement never
terminate, causing an infinite loop.
An attacker able to submit HTML/CSS to a fulgur-based conversion service can
trigger this with a trivially small payload, denying service to the host and any
co-tenants.
Fixed in 0.19.0: a MAX_PAGES cap bounds the slice loop — halting it even for a
+inf height — and non-finite layout heights are sanitized so they can no
longer drive the loop.
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 the Attack
Vector is assessed as Network for the reasonable worst-case deployment — a
network-facing service that renders untrusted 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).
Advisory available under CC0-1.0
license.