Considerato che in questi giorni il 30%-35% del totale della posta sul
nostro server è stato generato da tentativi di consegna di virus e che
in più ci si mettono anche le notifiche .... trovo la riflessione che
segue quantomeno interessante.
ciao
Lucia
-------- Original Message --------
Subject: RFC: virus handling
Date: Wed, 28 Jan 2004 16:45:39 +0100
From: Thomas Zehetbauer <thomasz@xxxxxxxxxxxxxx>
To: bugtraq@xxxxxxxxxxxxxxxxx
Looking at the current outbreak of the Mydoom.A worm I would like to
share and discuss some thoughts:
1.) Virus Detected Notifications
After filtering out the messages generated by the worm itself there
remain a lot of messages generated by automated e-mail scanning
solutions.
1.1.) Configuration
Unless the virus scanner provides special handling for worms and virii
which knowingly use a faked sender address it should not send out
notification messages unless the administrator has been warned that
these notification messages may not reach the intended recipient and has
still enabled this feature.
1.2.) Format
These messages cannot be easily filtered because they come in many
different formats and do often not contain any useful information at
all.
1.2.1.) Standardization
To allow filtering of these messages they should always carry the text
'possible virus found' in the subject optionally extended by the name of
the virus or the test conducted (eg. heuristics).
1.2.2.) Virus Information
The message should always include the name of the virus found or the
test conducted (eg. forbidden file type).
1.1.2.) Original Message
The notification should never include the original message sent as
otherwise it may send the worm/virus to a previously unaffected third
party or re-infect a system that has already been cleaned.
1.2.) Notification
Regarding wasted time and storage capacity the false notifications sent
out to innocent third parties by many systems are already causing more
damage than the actual worm or virus. Given the current situation of
many unaware or ignorant administrators everyone capable to do so should
tell these people to fix their badly configured e-mail scanners.
2.) Non Delivery Notifications
It seems that this worm is trying to avoid people getting treacherous
non delivery notifications by using obviously faked but otherwise
plausible e-mail addresses. This may cause double bounce messages or
even message loops at badly configured sites.
2.1.) Avoid
Virus filters should therefore be designed and implemented before
checking the legitimacy of the intended recipient. This would also avoid
helping the virus spread by bouncing it to a previously unaffected third
party.
3.) ISPs
It is worth to note that once again primarily individuals using a
commercial provider have been affected by this worm.
3.1.) Notification
As these people do mostly not run a SMTP server on their system it is
unfortunately almost impossible to contact them when only knowing their
IP address.
3.1.1.) Abuse Role Account
Providers should provide an adequately stuffed abuse role account to
allow the affected users beeing notified. To ease efficiency messages
sent there should include the IP address, the exact time and date of the
incident and the name of the virus on the subject line.
3.1.2.) e-mail Alias and Web-Interface
Additionally providers should provide e-mail aliases for the IP
addresses of their customers (eg. customer at 127.0.0.1 can be reached
via 127.0.0.1@xxxxxxxxxxxx) or a web interface with similiar
functionality. The latter should be provided when dynamically assigned
IP addresses are used for which an additional timestamp is required.
3.2.) Disconnect
Providers should grant their customers some grace period to clean their
infection and should thereafter be disconnected entirely or filtered
based on protocol (eg. outgoing SMTP) or content (eg. transparent
smarthost with virus scanner) until they testify that they have cleaned
their system.
Regards
Tom
--
T h o m a s Z e h e t b a u e r ( TZ251 )
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