CVE-2021-38196: 
Rust vulnerability analysis and mitigation

An issue was discovered in the better-macro crate through 2021-07-22 for Rust. The crate intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose. The vulnerability is tracked as CVE-2021-38196 with a CVSS v3.1 base score of 9.8 (CRITICAL) (NVD).

The vulnerability exists in the better-macro crate's println function for versions >1.0.0. The crate was created specifically to demonstrate that proc-macros can be used to execute arbitrary code. It opens a URL (https://github.com/raycar5/better-macro/blob/master/doc/hi.md) which, while not currently malicious, could potentially be changed to serve malicious content (RustSec Advisory).

The vulnerability allows remote attackers to execute arbitrary code through proc-macros. While the current implementation only opens a non-malicious URL, the potential impact is critical as it could be modified to execute malicious code (RustSec Advisory).

There are no patches available for this vulnerability. The only mitigation is to avoid using the better-macro crate entirely, as it has no legitimate purpose or functionality (RustSec Advisory).