Rsync, a versatile file-synchronizing tool, contains six vulnerabilities present within versions 3.3.0 and below. Rsync can be used to sync files between remote and local computers, as well as storage devices. The discovered vulnerabilities include heap-buffer overflow, information leak, file leak, external directory file-write,–safe-links bypass, and symbolic-link race condition.

On January 14, Nick Tait announced the discovery of six vulnerabilities in rsync, the popular file-synchronization tool. While software vulnerabilities are not uncommon, the most serious one he announced allows for remote code execution on servers that run rsyncd — and possibly other configurations. The bug itself is fairly simple, but this event provides a nice opportunity to dig into it, show why it is so serious, and consider ways the open-source community can prevent such mistakes in the future.

The vulnerabilities were found by two groups of researchers: Simon Scannell, Pedro Gallegos, and Jasiel Spelman from Google's Cloud Vulnerability Research identified five of them, including the most serious one. Aleksei Gorban, a security researcher at TikTok, discovered the sixth — a race condition in how rsync handles symbolic links.