FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

FreeBSD -- Resource exhaustion due to sessions stuck in LAST_ACK state

Affected packages
10.1 <= FreeBSD-kernel < 10.1_15
9.3 <= FreeBSD-kernel < 9.3_20
8.4 <= FreeBSD-kernel < 8.4_34


VuXML ID 0c064c43-600a-11e6-a6c3-14dae9d210b8
Discovery 2015-07-21
Entry 2016-08-11

Problem Description:

TCP connections transitioning to the LAST_ACK state can become permanently stuck due to mishandling of protocol state in certain situations, which in turn can lead to accumulated consumption and eventual exhaustion of system resources, such as mbufs and sockets.


An attacker who can repeatedly establish TCP connections to a victim system (for instance, a Web server) could create many TCP connections that are stuck in LAST_ACK state and cause resource exhaustion, resulting in a denial of service condition. This may also happen in normal operation where no intentional attack is conducted, but an attacker who can send specifically crafted packets can trigger this more reliably.


CVE Name CVE-2015-5358
FreeBSD Advisory SA-15:13.tcp