Microsoft security researchers Shuo
Chen, Ziqing Mao, Yi-Min
Wang, and Ming Zhang reported that when a
CONNECT request is sent to a proxy server and a non-200 response is
returned, then the body of the response is incorrectly rendered
within the context of the request Host: header. An
active network attacker could use this vulnerability to intercept a
CONNECT request and reply with a non-200 response containing malicious
code which would be executed within the context of the victim's
requested SSL-protected domain. Since this attack requires the victim
to have a proxy configured, the severity of this issue was determined
to be high.
Thunderbird mail messages are not vulnerable to this flaw, but if Thunderbird were being used in a browser-like manner (through Add-ons, perhaps) and JavaScript were enabled (not the default settng) then users could be vulnerable to this flaw in older versions.
Vulmon