Product Affected

This issue can affect any product or platform running Junos OS.
Medium
CVSS Base Score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)

Problem

For an established TCP session, TCP input validation only ensures that sequence numbers are within the acceptable window prior to examining whether the SYN flag is set on the segment. If the SYN flag is set, the TCP stack drops the session and sends a RST segment to the other side. Given that the SYN only needs to fall within the window, an attacker who can guess an in-window sequence number, source and destination address and port numbers can exploit this vulnerability to reset any established TCP session.

This issue only affects TCP sessions terminating on the router. Transit traffic and TCP Proxy services are unaffected by this vulnerability.

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue has been assigned CVE-2004-0230 .

Solution

Junos now implements the TCP robustness improvements outlined in Section 4 of RFC 5961. Junos will send an ACK in response to any SYN or RST flag received, irrespective of the sequence number.

The following software releases have been updated to resolve this specific issue: Junos OS 11.4R11, 12.1R10, 12.1X44-D35, 12.1X45-D25, 12.1X46-D20, 12.1X47-D10, 12.2R8, 12.3R6, 13.1R4, 13.2R4, 13.3R2, 14.1R1, and all subsequent releases (i.e. all releases built after 14.1R1).

This issue is being tracked as PR 935125 and is visible on the Customer Support website.

KB16765 [juniper.net] - "In which releases are vulnerabilities fixed?" describes which release vulnerabilities are fixed as per our End of Engineering and End of Life support policies.

How to obtain fixed software:

Security vulnerabilities in Junos are fixed in the next available Maintenance Release of each supported Junos version. In some cases, a Maintenance Release is not planned to be available in an appropriate time-frame. For these cases, Service Releases are made available in order to be more timely. Security Advisory and Security Notices will indicate which Maintenance and Service Releases contain fixes for the issues described. Upon request to JTAC, customers will be provided download instructions for a Service Release. Although Juniper does not provide formal Release Note documentation for a Service Release, a list of "PRs fixed" can be provided on request.

Workaround

  • Enable TCP authentication. Refer to Junos documentation for config options and examples.
  • Enable IPSec.
  • Enable the system to send ACKs for in-window RSTs and SYN packets on TCP connections via the ' set system internet-options tcp-reset-syn-acknowledge ' hidden configuration command.
  • Enable a stateful firewall to block SYN packets on existing sessions.

In addition to the recommendations listed above, it is good security practice to limit the exploitable attack surface of critical infrastructure networking equipment. Use access lists or firewall filters to limit access to the router via TCP only from trusted, administrative networks or hosts.

Severity Assessment

Information for how Juniper Networks uses CVSS can be found at KB 16446 [juniper.net] "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

Related Information

Acknowledgements