Cisco ASA and FTD SIP Inspection denial-of-service vulnerability

Overview

Cisco Adaptive Security Appliance (ASA) software and Cisco Firepower Threat Defense (FTD) software fails to properly parse SIP traffic, which can result in a denial-of-service condition on affected devices.

Description

Cisco Adaptive Security Appliance (ASA) software and Cisco Firepower Threat Defense (FTD) software fails to properly parse SIP traffic, which can allow an attacker to trigger high CPU usage, resulting in a denial-of-service condition on affected devices. This vulnerability is exposed if SIP Inspection is enabled on affected devices, which is the default configuration on ASA devices. The Cisco SIP Inspection feature is advertised to “… enforce the sanity of the SIP messages, as well as detect SIP-based attacks.”

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Impact

By causing an affected Cisco device to parse specially-crafted SIP traffic, a remote, unauthenticated attacker may be able to trigger a denial-of-service condition on affected devices.

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Solution

The CERT/CC is currently unaware of a practical solution to this problem. Please consider the following workarounds:

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Disable SIP Inspection

According to the Cisco advisory:

Disabling SIP inspection will completely close the attack vector for this vulnerability. However, it may not be suitable for all customers. In particular, disabling SIP inspection would break SIP connections if either NAT is applied to SIP traffic or if not all ports required for SIP communication are opened via ACL.

To disable SIP inspection, configure the following:

_ Cisco ASA Software and Cisco FTD Software Releases 6.2 and later (in FTD 6.2 and later use Cisco FMC to add the following via FlexConfig policy):_

_ policy-map global_policy_
_ class inspection_default_
_ _``**_no inspect sip_**

_ Cisco FTD Software Releases prior to 6.2:_

_ _**_configure inspection sip disable_**

Vendor Information

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Cisco Affected

Updated: November 01, 2018

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Vendor References

• <https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181031-asaftd-sip-dos&gt;

CVSS Metrics

Group	Score	Vector
Base	7.8	AV:N/AC:L/Au:N/C:N/I:N/A:C
Temporal	7.4	E:H/RL:W/RC:C
Environmental	5.5	CDP:ND/TD:M/CR:ND/IR:ND/AR:ND

References

• <https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181031-asaftd-sip-dos&gt;
• <https://www.cisco.com/c/en/us/products/security/adaptive-security-appliance-asa-software/index.html&gt;
• <https://www.cisco.com/c/en/us/support/docs/security/asa-5500-x-series-firewalls/212420-configure-firepower-threat-defense-ftd.html&gt;
• <https://www.cisco.com/c/en/us/td/docs/security/asa/asa96/configuration/firewall/asa-96-firewall-config/inspect-voicevideo.html#ID-2096-00000613&gt;
• <https://www.cisco.com/c/en/us/td/docs/security/asa/asa99/configuration/firewall/asa-99-firewall-config/inspect-voicevideo.pdf&gt;
• <https://en.wikipedia.org/wiki/Session_Initiation_Protocol&gt;

Acknowledgements

This vulnerability was publicly reported by Cisco.

This document was written by Will Dormann.

Other Information

CVE IDs:	CVE-2018-15454
Date Public:	2018-10-31 Date First Published: