Vulnerability GHSA-5w5r-mf82-595p

Critical
CRITICAL RISK
CVSS Score: 9.5
Score Range: 9.0–10.0
Critical severity vulnerabilities (CVSS 9.0–10.0). These represent the highest impact issues.
9 months ago
January 28, 2026 at 04:06 PM UTC
Cap'n Proto has Undefined Behavior in constant::Reader and StructSchema
0.0.1 - 0.23.2
0.0.1 - 0.23.2

Summary

Cap'n Proto has Undefined Behavior in constant::Reader and StructSchema

Details

The safe API functions constant::Reader::get and StructSchema::new rely on PointerReader::get_root_unchecked, which can cause undefined behavior (UB) by constructing arbitrary words or schemas.

Reader::get

pub fn get(&self) -> Result<<T as Owned>::Reader<'static>> {
    // ...
    // UNSAFE: access `words` without validation
}

StructSchema::new

pub fn new(builder: RawBrandedStructSchema) -> StructSchema {
    // ...
    // UNSAFE: access encoded nodes without validation
}

This vulnerability allows safe Rust code to trigger UB, which violates Rust's safety guarantees.

The issue is resolved in version 0.24.0 by making constructor functions unsafe and mark the fields of struct as visible only in the crate.

Impacted packages

Timeline

Published
9 months ago
January 28, 2026 at 04:06 PM UTC
Fixed (0.24.0)
10 months ago
December 24, 2025 at 08:20 PM UTC
Last Modified
9 months ago
February 03, 2026 at 03:06 AM UTC