An attacker was able to bypass the `connect-src`
directive of a Content Security Policy by manipulating
subdocuments. This would have also hidden the connections
from the Network tab in Devtools.
When Multi-Account Containers was enabled, DNS requests
could have bypassed a SOCKS proxy when the domain name was
invalid or the SOCKS proxy was not responding.
If a user visited a webpage with an invalid TLS
certificate, and granted an exception, the webpage was able to
provide a WebAuthn challenge that the user would be prompted
to complete. This is in violation of the WebAuthN spec which
requires "a secure transport established without
errors".
The exception page for the HTTPS-Only feature, displayed
when a website is opened via HTTP, lacked an anti-clickjacking
delay, potentially allowing an attacker to trick a user into
granting an exception and loading a webpage over HTTP.
If a user saved a response from the Network tab in Devtools
using the Save As context menu option, that file may not have
been saved with the `.download` file extension.
This could have led to the user inadvertently running a
malicious executable.
Memory safety bugs present in Firefox 139 and Thunderbird
139. Some of these bugs showed evidence of memory corruption
and we presume that with enough effort some of these could
have been exploited to run arbitrary code.