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2015-10 Security Bulletin: Junos: Corrupt pam.conf file allows unauthenticated root access (​CVE-2015-7751)

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Article ID: JSA10707 SECURITY_ADVISORIES Last Updated: 15 Oct 2015Version: 2.0
Product Affected:
This issue can affect any product or platform running Junos OS.​​
Problem:
When the pam.conf file is corrupted in certain ways, it may allow connection to the device as the root user with no password. This "fail-open" behavior allows an attacker who can specifically modify the file to gain full access to the device.

Note that inadvertent manipulation of the pam.conf by an authorized administrator can also lead to unauthenticated root access to the device. Extreme care should be taken by administrators to avoid modifying pam.conf directly.

While the standalone vulnerability may not be directly exploitable, this issue increases the severity of other attacks that may be chained together to launch a multi-stage advanced attack against the device.

This issue is assigned ​CVE-2015-7751.

Solution:
The following software releases have been updated to resolve this specific issue: Junos OS 12.1X44-D50, 12.1X46-D35, 12.1X47-D25, 12.3R9, 12.3X48-D15, 13.2R7, 13.2X51-D35, 13.3R6, 14.1R5, 14.1X50-D105, 14.1X51-D70, 14.1X53-D25, 14.1X55-D20, 14.2R1, 15.1F2, 15.1R1, 15.1X49-D10, and all subsequent releases.​

This issue was found during internal product security testing.

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

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

This issue is being tracked as PR 965378 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 CLI access to the router only from trusted hosts.

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 SSH or telnet only from trusted, administrative networks or hosts.

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.


Modification History:
Modification History:

2015-10-14: Initial publication
2015-10-15: Removed 'chflags' workaround which can cause operational issues in certain cases.

CVSS Score:
6.7 (CVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H)
Severity Level:
Medium
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories"
Acknowledgements:

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