Vulnerability Report:
As part of our recent work on the trust hierarchy that exists among email
providers throughout the Internet, we have uncovered a serious security flaw in
Ggoogle's free email service, Gmail. This vulnerability exposes Google's email
servers in a way that allows an attacker to use them as open spam and phishing
relays. This issue is related to the risk of a malicious user abusing Gmail's
email forwarding functionality. This is possible because Gmail's email
forwarding functionality does not impose proper security restrictions during
its setup process and can be easily subverted. By exploiting this problem an
attacker can send unlimited spam and phishing (i.e. forged) email messages that
are delivered by Google's very own SMTP servers. Since the messages are
delivered by Google's own servers, an attack based on this flaw is able to
bypass all spam filters that are based on the blacklist / whitelist concept. We
were able to confirm that this vulnerability is indeed exploitable b
y crafting a proof of concept attack that allowed us to send any number of
forged email messages without restriction through Google's server
infrastructure. We have also verified that this flaw allows attackers to bypass
spam filters by using our method to send messages that are usually flagged as
spam. While sending these messages directly from our network in the traditional
way had the messages classified as spam, by sending the very same messages
using our exploit, the messages were delivered directly to the victim's inbox,
thus bypassing filters.
Impact:
All email providers that offer Google's SMTP servers any special level of trust
(e.g. whitelist status) are vulnerable.
Disclosure:
We have contacted Google about this issue and are waiting for their position
before releasing further details.
For more information, visit our homepage:
http://ece.uprm.edu/~andre/insert
Regards,
Pablo Ximenes, André dos Santos
INSERT - Information Security Research Team
University of PR at Mayaguez (UPRM), USA
State University of Ceará (UECE), Brazil
pablo.ximenes@xxxxxxx, andre@xxxxxxxxxxxxx