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2012-04 Security Bulletin: Junos: User authorization can result in incorrect permissions

  [JSA10503] Show Article Properties


Legacy Advisory Id:
PSN-2012-04-545
Product Affected:
This issue can affect all Junos devices configured with access via SSH, and TACACS+ authorization or RADIUS VSA Juniper-Deny-Commands in use.
Problem:

After abnormal termination of an SSH session remotely authenticated using either TACACS+ for both authentication and authorization, or RADIUS returning the Juniper-Deny-Commands vendor-specific attribute (VSA), a permissions file based on the process ID (PID) of the session may not be cleaned up. As a result, it is possible for a future session matching the identical PID to inherit the authorization permissions of the previous session.

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

No other Juniper Networks products or platforms are affected by this issue.
Solution:

Users authenticated on a remote auth-server (RADIUS/TACACS+) have their fetched authorizations stored in a file called /var/run/PID.perm. On unclean exits of the SSH client, the /var/run/PID.perm file is not deleted by the SSH daemon. These stale /var/run/PID.perm files get referenced by future login sessions whose PID matches the PID of the stale /var/run/PID.perm file, thereby causing incorrect authorizations to get applied to the currently logged in user.

The sshd clean-up routines have been enhanced to remove the PID.perm file in all cases of expected or unexpected termination of an SSH session by the client.

All Junos OS software releases built on or after 2010-12-03 have fixed this specific issue. Releases containing the fix specifically include: 10.1R3, 10.2R2, 10.3R1, 10.4R1, and all subsequent releases (i.e. all releases built after 10.4R1).

This issue is being tracked as PR 388053 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:

Use access lists or firewall filters to limit access to the router via SSH only from trusted networks.
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:
7.1 (AV:N/AC:H/Au:S/C:C/I:C/A:C)
Severity Level:
High
Severity Assessment:
CVSS Temporal Score: 5.3 (AV:N/AC:H/Au:S/C:C/I:C/A:C/E:U/RL:O/RC:C)

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