AV:N/AC:L/Au:N/C:C/I:C/A:C/E:F/RL:OF/RC:C
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Cisco Unified Communications Manager (CUCM), formerly CallManager, contains two denial of service (DoS) vulnerabilities. Large volumes of UDP Session Initiation Protocol (SIP) INVITE messages may cause a resource exhaustion condition on CUCM systems resulting in a kernel panic. The CUCM Trivial File Transfer Protocol (TFTP) service contains a buffer overflow vulnerability that may result in a denial of service condition or allow a remote, unauthenticated user to execute arbitrary code. There are no workarounds for these vulnerabilities.
Cisco has made free software available to address these vulnerabilities for affected customers.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-cucm.
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Note: Cisco Unified CallManager versions 4.2, 4.3, 5.1 and 6.0 have been renamed Cisco Unified Communications Manager. CUCM versions 3.3, 4.0, 4.1 and 5.0 retain the Cisco Unified CallManager name.
Vulnerable Products
All Cisco Unified CallManager 5.0 versions and Communications Manager 5.1 versions prior to 5.1(2) are affected by the SIP INVITE UDP denial of service and TFTP service overflow vulnerabilities. Cisco Unified Communications Manager version 5.1(2) is affected by the SIP INVITE UDP denial of service vulnerability, but not the TFTP service overflow vulnerability.
Note: Cisco Unified Communications Manager version 6.0(1) shipped containing the fixes for these vulnerabilities.
Administrators of systems that are running CUCM versions 5.x and 6.x can determine the software version by viewing the main page of the CUCM Administration interface. The software version can also be determined by running the command show version active via the command line interface (CLI).
Products Confirmed Not Vulnerable
Cisco Unified CallManager versions 3.x, 4.0 and 4.1, Communications Manager 4.2 and 4.3, and Cisco CallManager Express are not affected by these vulnerabilities. No other Cisco products are currently known to be affected by these vulnerabilities.
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Cisco Unified Communications Manager (CUCM), formerly CallManager, is the call processing component of the Cisco IP Telephony solution that extends enterprise telephony features and functions to packet telephony network devices, such as IP phones, media processing devices, voice-over-IP (VoIP) gateways, and multimedia applications.
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SIP INVITE UDP Denial of Service:
The CUCM Session Initiation Protocol (SIP) stack contains a DoS vulnerability. By flooding a CUCM system with normal SIP INVITE messages to UDP port 5060, it may be possible to trigger a resource exhaustion condition that will result in a kernel panic. This vulnerability is corrected in CUCM versions 5.1(2b), 5.1(3) and 6.0(1). This issue is documented in Cisco bug ID CSCsi75822.
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Centralized TFTP File Locator Service Overflow:
The CUCM TFTP service contains a buffer overflow vulnerability in the processing of filenames that may allow a remote, unauthenticated user to cause a DoS condition or execute arbitrary code. The TFTP service serves files via two methods: traditional TFTP (UDP port 69), and a HTTP server that listens on TCP port 6970. The HTTP server component is known as the Centralized TFTP File Locator Service.
The Centralized TFTP File Locator Service allows CUCM administrators to store device configuration and software files in a central location. The Centralized TFTP File Locator Service becomes active when the CUCM TFTP service is enabled and an alternate TFTP path is configured. Please consult the following documentation for more information on configuring the Centralized TFTP File Locator Service and alternate TFTP paths:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/5_0_1/ccmsys/a02tftp.html#wp1044917
The overflow vulnerability only affects the Centralized TFTP File Locator Service component of the CUCM TFTP service. The Centralized TFTP File Locator Service is only used for communication between CUCM systems. The CUCM TFTP service is not enabled by default.
This vulnerability is corrected in CUCM versions 5.1(2), 5.1(3) and 6.0(1). This issue is documented in Cisco bug ID CSCsh47712.
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SIP INVITE UDP Denial of Service:
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There are no workarounds for these vulnerabilities.
Filtering traffic to affected CUCM systems on screening devices can provide a mitigation technique for both vulnerabilities:
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Permit access to UDP port 5060 only from valid SIP devices to
mitigate the SIP INVITE UDP DoS. Anti-spoofing measures should also be employed
to prevent UDP spoofing.
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Permit access to TCP port 6970 only from CUCM systems to mitigate the
Centralized TFTP File Locator Service overflow.
There is currently no method to configure filtering directly on a CUCM system.
Filters that deny SIP packets using UDP port 5060 and HTTP packets on TCP port 6970 should be deployed throughout the network as part of a transit access control list (tACL) policy for protection of traffic that enters the network at ingress access points. Filters for SIP packets using UDP port 5060 and HTTP packets on TCP port 6970 should be deployed in front of vulnerable network devices so that traffic is allowed from trusted clients only.
Additional information about tACLs is available in Transit Access Control Lists: Filtering at Your Edge:
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801afc76.shtml
Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory:
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Permit access to UDP port 5060 only from valid SIP devices to
mitigate the SIP INVITE UDP DoS. Anti-spoofing measures should also be employed
to prevent UDP spoofing.
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When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.
These vulnerabilities were discovered internally by Cisco.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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