2012-01 Security Bulletin: Junos: SSH allows forwarding of tunneled TCP traffic over an existing CLI connection

Legacy Advisory Id:PSN-2012-01-473

Product Affected:This issue affects all Junos routers configured to allow access via SSH.

Problem:After establishing a CLI session to a Junos router via SSH, it is possible to create an SSH tunnel over this session to forward TCP traffic. This effectively bypasses any firewall filters or ACLs, allowing access to the resources beyond the router. Note that SSH access lists still apply, and successful CLI authentication to the router is required. This issue was discovered by an external security researcher. Juniper SIRT is not aware of any malicious exploitation of this vulnerability. No other products or platforms are affected by this issue.This issue has been assigned CVE-2004-1653.

Solution:Starting with Junos 11.4R1, a new configuration option has been added to selectively disallow TCP port forwarding through an existing SSH CLI session:
user@junos# set system services ssh no-tcp-forwarding
Once enabled, new SSH sessions will not allow the forwarding of tunneled TCP traffic. All Junos OS software releases 11.4R1 and above include this new security enhancement. This issue is being tracked as PR 684130 and is visible on the Customer Support website. KB16765 – “In which releases are vulnerabilities fixed?” describes which release vulnerabilities are fixed as per our End of Engineering and End of Life support policies.

Workaround:Since this vulnerability simply allows an extension of access already granted by the user, allowing SSH access only from trusted networks will completely mitigate this issue. Acknowledgement Juniper SIRT would like to acknowledge and thank Ajay Kumar Upadhyay for responsibly reporting this vulnerability.

Implementation: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.

Related Links: CVSS Score:5.5 (AV:N/AC:L/Au:S/C:P/I:P/A:N)

Risk Level:Medium

Risk Assessment:Information for how Juniper Networks uses CVSS can be found at KB 16446 “Common Vulnerability Scoring System (CVSS) and Juniper’s Security Advisories.”

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