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AUSCERT External Security Bulletin Redistribution
Cisco Firepower Detection Engine SSL Decryption Memory
Consumption Denial of Service Vulnerability
5 October 2017
AusCERT Security Bulletin Summary
Product: Cisco Firepower Detection Engine
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2017-12245
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Cisco Firepower Detection Engine SSL Decryption Memory Consumption Denial of
2017 October 4 16:00 GMT
No workarounds available
Cisco Bug IDs:
A vulnerability in SSL traffic decryption for Cisco Firepower Threat Defense
(FTD) Software could allow an unauthenticated, remote attacker to cause
depletion of system memory. If this memory leak persists over time, a denial
of service (DoS) condition could develop because traffic can cease to be
forwarded through the device.
The vulnerability is due to an error in how the Firepower Detection Snort
Engine handles SSL traffic decryption and notifications to and from the
Adaptive Security Appliance (ASA) handler. An attacker could exploit this
vulnerability by sending a steady stream of malicious Secure Sockets Layer
(SSL) traffic through the device. An exploit could allow the attacker to cause
a DoS condition when the device runs low on system memory.
Cisco has released software updates that address this vulnerability. There are
no workarounds that address this vulnerability.
This advisory is available at the following link:
This vulnerability affects Cisco Firepower Threat Defense (FTD) Software
Releases 6.0.1 and later when the software is configured as described in this
section and is running on any of the following Cisco products:
Adaptive Security Appliance (ASA) 5500-X Series Next-Generation Firewalls
Firepower 2100 Series Security Appliances
Firepower 4100 Series Security Appliances
Firepower 9300 Series Security Appliances
Affected devices are vulnerable when they are configured for one or more SSL
inspection policies for Decrypt and Resign or Known Key. These features allow
the SSL traffic to be decrypted on the device for further inspection.
This vulnerability applies to FTD-supported releases only. These releases
contain both Firepower and ASA code. Review Firepower Threat Defense Devices
in the Cisco Firepower Compatibility Guide for additional information.
Administrators can use the CLI command show version to determine the FTD
release. In this example, the device is running software release 6.2.0.
> show version
---------------------[ ftd ]---------------------
Model : Cisco ASA5525-X Threat Defense (75) Version 6.2.0 (Build 362)
UUID : 2849ba3c-ecb8-11e6-98ca-b9fc2975893c
Rules update version : 2017-03-15-001-vrt
VDB version : 279
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this
Cisco has confirmed that this vulnerability does not affect the following
3000 Series Industrial Security Appliances (ISA)
Adaptive Security Appliance (ASA) 5000-X Series with FirePOWER Services
Adaptive Security Appliance (ASA) 5500-X Series with FirePOWER Services
Advanced Malware Protection (AMP) for Networks, 7000 Series Appliances
Advanced Malware Protection (AMP) for Networks, 8000 Series Appliances
FirePOWER 7000 Series Appliances
FirePOWER 8000 Series Appliances
Firepower Management Center
Firepower Threat Defense for Integrated Services Routers (ISRs)
Intrusion Prevention System (IPS) Software
Virtual Next-Generation Intrusion Prevention System (NGIPSv) for VMware
Cisco FTD is a unified software image that includes the ASA features and
Firepower services. This unified software is capable of offering the function
of ASA and Firepower in one platform, both in terms of hardware and software
Indicators of Compromise
Vulnerable devices are compromised when all the following conditions are met:
The device stops forwarding traffic.
The output of the show blocks command shows a zero count of a particular
memory block. This is most common for the memory blocks of size 2048 or 9344.
firepower# show blocks
SIZE MAX LOW CNT
0 1450 1448 1450
4 100 99 99
80 1000 950 984
256 4148 3898 4040
1550 6279 6184 6258
2048 15864 0 0
2560 164 164 164
4096 100 100 100
8192 100 100 100
9344 100 100 100
16384 102 102 102
65536 16 16 16
The output of the debug command show asp inspect-dp snort queues detail
debug shows the Receive Queue UtilizationRxQ (util)at 100 percent.
firepower# show asp inspect-dp snort queues detail debug
SNORT Inspect Instance Queue Configuration
RxQ-Size: 1 MB
TxQ-Size: 128 KB
TxQ-Data-Limit: 102.4 KB (80%)
TxQ-Data-Hi-Thresh: 35.8 KB (28%)
Id QId RxQ RxQ RxQ RxQ TxQ TxQ TxQ TxQ
(used) (util) (max used) (state) (used) (util) (max used) (state)
-- ---- ---------- ------ ---------- ---------------- ---------- ------ ---------- --------
0  2 MB 100% 2 MB READY 0 0% 2.1 KB READY
The output of the debug command show asp inspect-dp snort counters debug
zeros shows a count for Receive Queue Full (RxQ-Full) that is not zero.
firepower# show asp inspect-dp snort counters debug zeros SNORT Inspect
Id QId Type Name Value Raw-Value
-- ---- ---- ---- ---------- ----------
All All drop RxQ-Full 146.5 K (146546)
All All drop TxQ-Full 0 (0)
Contact the Cisco Technical Assistance Center (TAC) if additional assistance
is required to determine whether the device has been compromised by
exploitation of this vulnerability.
There are no workarounds that address this vulnerability.
Cisco has released free software updates that address the vulnerability
described in this advisory. Customers may only install and expect support for
software versions and feature sets for which they have purchased a license. By
installing, downloading, accessing, or otherwise using such software upgrades,
customers agree to follow the terms of the Cisco software license:
Additionally, customers may only download software for which they have a valid
license, procured from Cisco directly, or through a Cisco authorized reseller
or partner. In most cases this will be a maintenance upgrade to software that
was previously purchased. Free security software updates do not entitle
customers to a new software license, additional software feature sets, or
major revision upgrades.
When considering software upgrades, customers are advised to regularly consult
the advisories for Cisco products, which are available from the Cisco Security
Advisories and Alerts page, to determine exposure and a complete upgrade
In all cases, customers should ensure that the devices to be upgraded contain
sufficient memory and confirm that current hardware and software
configurations will continue to be supported properly by the new release. If
the information is not clear, customers are advised to contact the Cisco TAC
or their contracted maintenance providers.
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service
contract and customers who make purchases through third-party vendors but are
unsuccessful in obtaining fixed software through their point of sale should
obtain upgrades by contacting the Cisco TAC:
Customers should have the product serial number available and be prepared to
provide the URL of this advisory as evidence of entitlement to a free upgrade.
Customers should upgrade to an appropriate release as indicated in the table
in this section. To help ensure a complete upgrade solution, consider that
this advisory is part of a collection that includes the following advisories:
cisco-sa-20171004-fpsnort: Cisco Firepower Detection Engine IPv6 Denial of
cisco-sa-20171004-ftd: Cisco Firepower Detection Engine SSL Decryption
Memory Consumption Denial of Service Vulnerability
In the following table, the left column lists major releases of Cisco
software. The center column indicates whether a major release is affected by
the vulnerability described in this advisory and the first minor release that
includes the fix for this vulnerability. The right column indicates whether a
major release is affected by all the vulnerabilities described in this
collection of advisories and the current recommended release for those
Exploitation and Public Announcements
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any
public announcements or malicious use of the vulnerability that is described
in this advisory.
This vulnerability was found during resolution of a Cisco TAC support case.
Version Description Section Status Date
1.0 Initial public release. - Final 2017-October-04
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