Navigation Bar Top Applications Support Documentation Vendors Search Index Top Top

kernel -- TCP connection stall denial of service


Problem Description

Two problems have been discovered in the FreeBSD TCP stack.

First, when a TCP packets containing a timestamp is received, inadequate checking of sequence numbers is performed, allowing an attacker to artificially increase the internal "recent" timestamp for a connection.

Second, a TCP packet with the SYN flag set is accepted for established connections, allowing an attacker to overwrite certain TCP options.


Using either of the two problems an attacker with knowledge of the local and remote IP and port numbers associated with a connection can cause a denial of service situation by stalling the TCP connection. The stalled TCP connection my be closed after some time by the other host.


In some cases it may be possible to defend against these attacks by blocking the attack packets using a firewall. Packets used to effect either of these attacks would have spoofed source IP addresses.



portaudit: kernel -- TCP connection stall denial of service

Disclaimer: The data contained on this page is derived from the VuXML document, please refer to the the original document for copyright information. The author of portaudit makes no claim of authorship or ownership of any of the information contained herein.

If you have found a vulnerability in a FreeBSD port not listed in the database, please contact the FreeBSD Security Officer. Refer to "FreeBSD Security Information" for more information.

Oliver Eikemeier <>