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             AUSCERT External Security Bulletin Redistribution

       A vulnerability has been identified in Juniper platforms and
                         products running Junos OS
                               7 August 2018


        AusCERT Security Bulletin Summary

Product:           Juniper Junos
Publisher:         Juniper Networks
Operating System:  Juniper
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-5390  

Reference:         ESB-2018.2275

Original Bulletin: 

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2018-08 Out of Cycle Security Bulletin: Junos platforms vulnerable to
SegmentSmack attack [VU#962459]

Article ID:        JSA10876
Last Updated:      06 Aug 2018
Version:           1.0
- -------------------------------------------------------------------------------
Product Affected:
This issue affects all products and platforms running Junos OS
On August 6, 2018, the CERT/CC published VU#962459 describing a Linux kernel
TCP implementation denial of service vulnerability.  This issue, informally
called "SegmentSmack", relies upon a crafted set of TCP segments over an
established TCP session to create a resource denial of service.  Internal
testing has confirmed that both Linux-based (WRL, CentOS, RHEL) systems and
FreeBSD-based products and platforms running Junos OS are vulnerable to the
SegmentSmack attack (CVE-2018-5390).

Crafted sequences of TCP/IP packets may allow a remote attacker to create a
denial of service (DoS) condition on routing engines (REs) running Junos OS.
The attack requires a successfully established two-way TCP connection to an
open port.  The rate of attack traffic is lower than typical thresholds for
built-in Junos OS distributed denial-of-service (DDoS) protection, so
additional configuration is required to defend against these issues on affected
platforms.  Refer to the WORKAROUND section for additional guidance.

This issue was discovered by an external security researcher.

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

This issue has been assigned CVE-2018-5390.

Platforms confirmed to be vulnerable include, but are not limited to:

  o MX80
  o MX480
  o QFX5100
  o NFX 150/250
  o QFX5100
  o QFX5200
  o QFX10008
  o PTX10008
  o vMX, vSRX, vQFX, vPTX, etc.

Other platforms are still under investigation and continue to be tested by the
Juniper SIRT.

Since the attack requires a successfully established two-way TCP connection to
an open port, security best current practice of limiting the exploitable attack
surface of critical infrastructure networking equipment will mitigate this
issue.  Refer to the WORKAROUND section for additional guidance.

As software releases are updated to resolve this specific issue, this Juniper
Security Advisory (JSA) will be updated.

The TCP segment attack can be mitigated by using access lists or firewall
filters to limit access to the device only from trusted hosts.  Enable source
address validation such as uRPF to defend against attacks that rely upon an
established two-way TCP session to a reachable open port.

Additionally, the following IDP anomaly signatures may reduce the risk to
devices from these types of attacks:

Description: This protocol anomaly triggers when it detects a TCP Reassembler
that has exhausted all allocated memory for storing unacknowledged packets
Recommended action: Drop

Note: Memory threshold for the IDP-reassembler can be configured using IDP
sensor configuration.

Description: This protocol anomaly triggers when it detects that the TCP
Reassembler has too many packets stored in memory for a connection. This can
indicate an anti-IDS attack. This anomaly can be ignored in sniffer mode or in
case of asymmetric routing.
Recommended action: Drop

Note: Memory threshold for per flow in-memory segments can be configured using
IDP sensor configuration.

Software Releases, patches and updates are available at https://www.juniper.net
Modification History:

  o 2018-08-06: Initial Publication

Related Links:

  o KB16613: Overview of the Juniper Networks SIRT Quarterly Security Bulletin
    Publication Process

  o KB16765: In which releases are vulnerabilities fixed-

  o KB16446: Common Vulnerability Scoring System (CVSS) and Juniper's Security

  o Report a Vulnerability - How to Contact the Juniper Networks Security
    Incident Response Team

  o CVE-2018-5390: TCP denial of service

CVSS Score:
7.5 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Risk Level:
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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