Cisco IOS Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service condition.† Updates are available.
Cisco IOS Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability is in the affected device when it handles crafted Session Initiation Protocol (SIP) packets.† An unauthenticated, remote attacker could exploit this vulnerability by sending crafted SIP packets to the affected system.† When the affected device tries to process these packets, an unspecified error could occur that could cause the device to reload, resulting in a DoS condition.
Cisco has confirmed this vulnerability and released updated software.
Cisco has published a list of affected Cisco IOS Software releases in the security advisory.† The Vendor Announcements section of this alert contains a link to the advisory.
Only devices with SIP voice services enabled are vulnerable.† Further, to be vulnerable, the devices must have enabled the Cisco Unified Border Element feature.† More detailed information about determining whether a device is affected by this vulnerability is in the vendor advisory.
Because this vulnerability can be exploited using UDP, it is possible for an attacker to spoof the source address of the malicious SIP packets.† This spoofing could make it harder to determine where the attacks are coming from, and it could also be used to bypass IP-based ACLs if the attacker can determine which IP addresses are allowed to access the affected systems.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
An unauthenticated, remote attacker could exploit this vulnerability to cause a DoS condition on the affected device.† Repeated attacks could result in a persistent DoS condition.
The vulnerability is in the SIP processing component of the affected systems when it handles crafted SIP messages.† An unauthenticated, remote attacker could exploit this vulnerability by sending a series of crafted SIP messages to the affected system on TCP or UDP†port 5060 or TCP port 5061.† When the system tries to process these packets, it may reload, resulting in a DoS condition.
Administrators are advised to apply the appropriate updates.
Administrators are advised to implement anti-spoofing techniques at the network edge.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems†on the affected ports.
The Cisco Applied Intelligence team has created the following companion document to guide administrators in identifying and mitigating attempts to exploit this vulnerability prior to applying updated software: cisco-amb-20090923-voice
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 e-mail at firstname.lastname@example.org.
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