Rust advisories / cxx
UnsoundRUSTSEC-2026-0202 · cxx
RUSTSEC-2026-0202: `let_cxx_string!` uses uninitialized value due to exception safety violations
Short answercxx has an API that can cause undefined behaviour from safe code: `let_cxx_string!` uses uninitialized value due to exception safety violations. Fixed in 1.0.195.
| Crate | cxx |
|---|---|
| Type | Unsound (memory-exposure) |
| Affected versions | Before 1.0.195. |
| Fixed in | 1.0.195 |
| Severity | not scored |
| Published | 2026-07-05 |
| Last changed | 2026-07-05 |
| Also known as | none |
| Affected functions | cxx::let_cxx_string |
What to do
- See which version you have:
cargo tree -i cxx(it also shows which of your dependencies pulls it in). - Update within your version requirement:
cargo update -p cxx. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for examplecxx = "1.0.195") or update the dependency that pulls it in. - Check again with
cargo audit, or paste your Cargo.lock into our Cargo.toml checker.
Details from the advisory
In affected versions of this crate, let_cxx_string! is not exception safe. After creating the StackString, if match $value panics, the content of StackString is not yet initialized, while the drop implementation of StackString unconditionally deinitializes the content, leading to use of uninitialized value.
The soundness issue was fixed in version 1.0.195 by moving drop logics to separate drop guard after initializing the StackString.
References
- Package: crates.io/crates/cxx
- Advisory: rustsec.org/advisories/RUSTSEC-2026-0202.html
- Report: github.com/dtolnay/cxx/issues/1729
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
Up next
Are you affected?Check your whole dependency treePaste Cargo.lock: every advisory, for your exact versions.Read it next →Also worth your time
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