FreeBSD syncache "inpcb" pointer denial of service

bsd-syncache-inpcb-dos (8875) The risk level is classified as MediumMedium Risk


FreeBSD creates a syncache entry when a SYN packet arrives at the listen socket. If the program that created the socket was stopped and then restarted, the syncache entry would reference the previous "inpcb" pointer, which would cause the system to crash. The system must be restarted in order to regain normal functionality.


Denial of Service


Upgrade to the latest version of FreeBSD (4.5-STABLE dated 2002-02-21 or later), as listed in FreeBSD Security Advisory FreeBSD-SA-02:20. See References.

— OR —

Apply the appropriate path for this vulnerability, as listed in FreeBSD Security Advisory FreeBSD-SA-02:20. See References.


  • FreeBSD Security Advisory FreeBSD-SA-02:20: syncache/syncookies denial of service.
  • BID-4524: FreeBSD 4.5 syncache / syncookies Denial Of Service Vulnerability
  • CVE-2002-0518: The SYN cache (syncache) and SYN cookie (syncookie) mechanism in FreeBSD 4.5 and earlier allows remote attackers to cause a denial of service (crash) (1) via a SYN packet that is accepted using syncookies that causes a null pointer to be referenced for the socket's TCP options, or (2) by killing and restarting a process that listens on the same socket, which does not properly clear the old inpcb pointer on restart.
  • OSVDB ID: 6046: FreeBSD syncache/syncookie TCP Socket DoS

Platforms Affected:

  • FreeBSD FreeBSD 4.5


Apr 16, 2002

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