```toml
[advisory]
id = "CVE-2017-20004"
package = "std"
categories = ["thread-safety"]
date = "2017-04-29"
url = "https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-20004"

[versions]
patched = [">= 1.19.0"]
unaffected = ["< 1.0.0"]
```

# MutexGuard\<Cell\<i32\>\> must not be Sync

In the standard library in Rust before 1.19.0, there is a synchronization problem in the MutexGuard object. MutexGuards can be used across threads with any types, allowing for memory safety issues through race conditions.