GHSA-5w5r-mf82-595p

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

Published 28 Jan 2026Modified 28 Jan 2026

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

GHSA9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Trivy's own label is CRITICAL. Rated critical by GHSA.

Description

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

Affected packages and fixed versions

Source	Package	Fixed in
cargo::GitHub Security Advisory Rust	capnp	0.24.0

References

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