A [critical vulnerability](https://www.mozilla.org/en-US/security/advisories/mfsa2020-49/)was discovered in the JavaScript engine of *Firefox* and *Tor Browser*.
Until Tails 4.13 (November 17), we recommend all users to set the [[security level of *Tor Browser*|doc/anonymous_internet/Tor_Browser#security-level]] to *Safer* or *Safest*.
This vulnerability was discovered during the [Tianfu Cup 2020 International Cybersecurity Contest](http://www.tianfucup.com/). The details of the vulnerability were not disclosed.