The Rust team was recently notified of a security vulnerability affecting the standard library's str::repeat function. When passed a large number this function has an integer overflow which can lead to an out of bounds write. If you are not using str::repeat, you are not affected.

We're in the process of applying for a CVE number for this vulnerability. Fixes for this issue have landed in the Rust repository for the stable/beta/master branches. Nightlies and betas with the fix will be produced tonight, and 1.29.1 will be released on 2018-09-25 with the fix for stable Rust.

You can find the full announcement on our rustlang-security-announcements mailing list here.