# RUSTSEC-2026-0202: `let_cxx_string!` uses uninitialized value due to exception safety violations

> Attackers can trigger use of uninitialized memory via panics in let_cxx_string!, potentially causing crashes or code execution in Rust applications using this crate.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Jul 2026

## What is RUSTSEC-2026-0202?

RUSTSEC-2026-0202 is an use after free vulnerability in cxx, published on 5 Jul 2026. 

### Official description

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`.

## Which versions are affected by RUSTSEC-2026-0202?

1 open source package ship an affected version, including cxx.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `cxx` | crates.io | From 0.0.0-0 | 1.0.195 |

## How do I fix RUSTSEC-2026-0202?

Upgrade cxx to 1.0.195 or later.

## Is RUSTSEC-2026-0202 being exploited?

There is no known exploitation of RUSTSEC-2026-0202 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0202 and fix it if it is affected.

What it is: RUSTSEC-2026-0202 is an use after free vulnerability in cxx, published on 5 Jul 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0202 in the wild and no public exploit code.

Affected packages and fixed versions:
- cxx (crates.io): affected from 0.0.0-0; fixed in 1.0.195

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/RUSTSEC-2026-0202/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0202/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0202

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0202/
Summaries are generated and may contain mistakes; the official description above is the record.