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TITLE:
Mozilla / Thunderbird Valid Email Address Enumeration Weakness

SECUNIA ADVISORY ID:
SA13086

VERIFY ADVISORY:
http://secunia.com/advisories/13086/

CRITICAL:
Not critical

IMPACT:
Exposure of system information

WHERE:
>From remote

SOFTWARE:
Mozilla 1.7.x
http://secunia.com/product/3691/
Mozilla Thunderbird 0.x
http://secunia.com/product/2637/

DESCRIPTION:
plonk has discovered a weakness in Mozilla and Thunderbird, which can
be exploited by malicious people to enumerate valid email addresses.

The weakness is caused due to an improper behaviour where references
to external stylesheets in HTML documents are followed. This can be
exploited to validate the existence of an mail address when a
malicious mail is opened.

The weakness has been confirmed in Mozilla 1.7.3 and Thunderbird 0.8.
Other versions may also be affected.

SOLUTION:
If this is considered a problem, then disable HTML support in
emails:
"View" --> "Message Body As" --> "Plain Text"

PROVIDED AND/OR DISCOVERED BY:
plonk

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