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DHCP Relay Agent can be tricked into snooping unicast DHCP traffic not configured on router

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Article ID: JSA10481 SECURITY_ADVISORIES Last Updated: 09 May 2013Version: 1.0
Legacy Advisory Id:
PSN-2011-07-300
Product Affected:
This issue can affect any MX Series, M120 or M320 router configured as a DHCP Relay Agent.
Problem:

The initial implementation of the Junos OS Extended DHCP Relay Agent feature failed to check whether unicast DHCP relay packets were received from trusted, known DHCP servers. The DHCP Relay Agent would simply intercept any unicast DHCP reply packets, if they passed through an interface which has the Extended DHCP Relay Agent enabled. This would in turn cause a DHCP binding and an access-internal route to be installed for the DHCP reply.

A malicious DHCP server could be configured to send crafted unicast DHCP reply packets through the router, which could cause the resultant access-internal routes to redirect traffic.
Solution:

Support for a new 'forward-snooped-clients' configuration option in the Extended DHCP Relay Agent was added in the releases listed below.

All JUNOS software releases built on or after 2010-12-08 have fixed this specific issue. Releases containing the fix specifically include: 10.0R4, 10.1R3, 10.2R2, 10.3R1, and all subsequent releases (i.e. all releases built after 10.3R1).

This issue is being tracked as PR 523902. While this PR may not be viewable by customers, it can be used as a reference when discussing the issue with JTAC.

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:

No known workaround exists for this issue.
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.
CVSS Score:
6.4 (AV:A/AC:M/Au:N/C:N/I:P/A:C/E:P/RL:U/RC:C)
Severity Level:
High
Severity 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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