CVE-2021-33503

### Impact When provided with a URL containing many `@` characters in the authority component the authority regular expression exhibits catastrophic backtracking causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect. ### Patches The issue has been fixed in urllib3 v1.26.5. ### References - [CVE-2021-33503](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-33503) - [JVNVU#92413403 (English)](https://jvn.jp/en/vu/JVNVU92413403/) - [JVNVU#92413403 (Japanese)](https://jvn.jp/vu/JVNVU92413403/) - [urllib3 v1.26.5](https://github.com/urllib3/urllib3/releases/tag/1.26.5) ### For more information If you have any questions or comments about this advisory: * Ask in our [community Discord](https://discord.gg/urllib3) * Email [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)