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The vulnerability stems from how the lopdf library processes PDF file structures, specifically when parsing nested arrays and dictionaries within the document catalog. During the parsing phase, functions such as `load_mem` recursively descend into these nested elements without enforcing any maximum recursion depth limit. When an attacker crafts a malicious PDF file containing thousands of deeply nested levels—such as an array nested over ten thousand times—the continuous recursive function calls rapidly consume all available stack memory space. This unchecked consumption causes a fatal stack overflow condition. Unlike standard application-level errors or panics in Rust, which can sometimes be safely caught and handled using `catch_unwind` mechanisms, a stack overflow results in an immediate and uncatchable process abort via SIGABRT. Consequently, any backend service, web API, or utility tool that ingests untrusted PDF files using vulnerable versions of lopdf can be completely disabled using a very small, lightweight file of roughly 21 kilobytes. This triggers a total denial of service across dependent systems without requiring complex memory corruption techniques or administrative privileges, presenting a severe availability risk for applications processing user-submitted documents.
DailyCVE Form:
Platform: lopdf
Version: 0.41.0 and earlier
Vulnerability : Stack Overflow
Severity : High
date : June 26, 2026
Prediction: June 2026
What Undercode Say:
Analytics: The vulnerability represents an uncontrolled recursion flaw leading to stack exhaustion and service denial. The risk vector relies on parsing malformed input structures locally or remotely via untrusted PDF parsing pipelines.
Bash commands and codes:
cargo add lopdf@=0.42.0 cargo update -p lopdf
fn main() {
let bytes = std::fs::read("poc.pdf").unwrap();
let _ = lopdf::Document::load_mem(&bytes);
}
Exploit: (Educational Purposes!)
To test and validate this denial of service behavior, a minimal proof of concept can be constructed by generating an excessively nested sequence of arrays within the PDF Catalog dictionary. An equivalent programmatic payload can be represented as:
let poc_data = "[" .repeat(10380) + &"]".repeat(10380);
Passing this payload into vulnerable versions of `lopdf::Document::load_mem` triggers unconstrained recursion, exhausting the thread stack and instantly aborting the runtime environment with SIGABRT.
Protection: from this CVE
Developers must update the lopdf dependency to version 0.42.0 or higher, where built-in parser safeguards enforce a maximum object-nesting depth limit and return an error instead of unbounded recursion. Implementing input sanitation or process isolation for PDF parsing tasks can also mitigate service-wide crashes.
Impact:
The impact is a complete denial of service across applications utilizing vulnerable library versions. Because the underlying stack overflow forces a hard process termination via SIGABRT that bypasses panic handlers, worker threads or host services crash instantly, causing persistent application downtime and service unavailability.
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Sources:
Reported By: github.com
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