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2015-10 Security Bulletin: Junos: SSH allows unauthenticated remote user to consume large amounts of resources (CVE-2015-7752)

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Article ID: JSA10708 SECURITY_ADVISORIES Last Updated: 30 Oct 2015Version: 2.0
Product Affected:
This issue can affect any product or platform running Junos OS.​​
Problem:
The SSH server used in Junos allows an unauthenticated remote attacker to consume large amounts of CPU time prior to authentication, possibly leading to a partial Denial of Service attack. The attacker must be able to reach the device via SSH through any existing access lists or firewall filters, and the issue only occurs if SSH is enabled.
​​
This issue is assigned CVE-2015-7752.
Solution:
A new configuration parameter, 'max-pre-authentication-packets', was added to allow specification of the maximum number of pre-auth SSH packets permitted per connection:

[system services ssh max-pre-authentication-packets]

The default is 128.

The following software releases have been updated to address this specific issue: Junos OS 12.1X44-D50, 12.1X46-D35, 12.1X47-D25, 12.3R10, 12.3X48-D10, 13.2R8, 13.2X51-D35, 13.3R6, 14.1R5, 14.1X53-D25, 14.2R3, 15.1R1, 15.1X49-D20, 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.

This issue is being tracked as PR 1058906 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 device via SSH only from trusted 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
2015-10-30: Added more detail about the new configuration parameter.

CVSS Score:
5.3 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L)
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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