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Mozilla Firefox < 37.0.1 HTTP/2 Alt-Svc Header SSL MitM

Medium

Synopsis

The remote host has a web browser installed that is vulnerable to a man-in-the-middle (MitM) attack.

Description

Versions of Mozilla Firefox earlier than 37.0.1 are affected by an error related to the HTTP/2 'Alt-Svc' header and SSL certificate verification, which allows man-in-the-middle (MitM) attacks. Specifically, this affects the script 'modules/libpref/init/all.js' as certificates are not properly validated when handling an Alt-Svc header in an HTTP/2 response. By spoofing the TLS/SSL server via a certificate that appears valid, an attacker with the ability to intercept network traffic (e.g. MiTM, DNS cache poisoning) can disclose and optionally manipulate transmitted data.

Solution

Upgrade to Firefox 37.0.1 or later.