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AUSCERT External Security Bulletin Redistribution
Cisco AsyncOS for Cisco Email Security Appliance Cluster
Denial of Service Vulnerability
16 July 2015
AusCERT Security Bulletin Summary
Product: Cisco Email Security Appliance
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2015-4236
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Cisco AsyncOS for Cisco Email Security Appliance Cluster Denial of Service
Threat Type: CWE-399: Resource Management Errors
IntelliShield ID: 39785
First Published: 2015 July 10 15:40 GMT
Last Published: 2015 July 10 15:40 GMT
Port: Not available
Urgency: Unlikely Use
Severity: Mild Damage
CVSS Base: 5.0
CVSS Temporal: 4.1
Version Summary: Cisco AsyncOS for Cisco Email Security Appliance contains a
vulnerability that could allow an unauthenticated, remote attacker to cause a
denial of service condition. Updates are available.
A vulnerability in the clustering component of Cisco AsyncOS for Cisco Email
Security Appliance (ESA) could allow an unauthenticated, remote attacker to
cause the device to become unresponsive on the clustering and SSH configured
The vulnerability is due to improper handling of packets sent at a high rate
when the system is configured for clustering. An attacker could exploit this
vulnerability by sending packets to the targeted system at a high rate. An
exploit could allow the attacker to cause the affected system to become
unresponsive on the clustering and SSH configured ports, causing all new
connections to these ports to fail. A reload is required to restore normal
Cisco has confirmed the vulnerability and released software updates.
At the time this alert was first published, Cisco ESA releases 8.5.6-073,
8.5.6-074, and 9.0.0-461 were vulnerable. Later releases of Cisco ESA may also
To exploit this vulnerability, an attacker would need to send packets to the
affected device at a high rate, making exploitation more difficult in
environments that restrict access to untrusted sources.
Cisco indicates through the CVSS score that functional exploit code exists;
however, the code is not known to be publicly available.
Cisco has released bug IDs CSCur13704 and CSCuq05636 for registered users,
which contains additional details and an up-to-date list of affected product
An unauthenticated, remote attacker could exploit this vulnerability to cause
an affected device to become unresponsive on the clustering and SSH configured
ports, resulting in a denial of service (DoS) condition.
The vulnerability is due to improper handling of packets sent at high rate to
an affected system that is configured for clustering.
An unauthenticated, remote attacker could exploit this vulnerability by
sending packets to the target system at a high rate. An exploit could allow
the attacker to cause the affected system to become unresponsive on the
clustering and SSH configured ports, resulting in a DoS condition.
Administrators are advised to apply the appropriate updates.
Administrators are advised to allow only trusted users to have network access.
Administrators are advised to monitor affected systems.
Cisco customers with active contracts can obtain updates through the Software
Center at the following link: Cisco. Cisco customers without contracts can
obtain upgrades by contacting the Cisco Technical Assistance Center at
1-800-553-2447 or 1-408-526-7209 or via email at firstname.lastname@example.org.
The security vulnerability applies to the following combinations of products.
Cisco Cisco Email Security Appliance (ESA) 9.0 .0-461 | 8.5 .6-074, .6-073
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The urgency and severity ratings of this alert are not tailored to individual
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configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED
THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF
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TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES
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