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 H.323 packets. An unauthenticated, remote attacker could exploit this vulnerability by sending crafted H.323 packets to the affected system. When the 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.
Indicators of Compromise
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.
The vulnerability is in the H.323 processing component of the affected systems when it handles crafted H.323 packets. An unauthenticated, remote attacker could exploit this vulnerability by sending a series of crafted H.323 packets to the affected system on TCP port 1720. When the system tries to process these packets, it may reload, resulting in a DoS condition.
Only devices that are configured to process H.323 messages are vulnerable. H.323 message processing is disabled by default. Details on how to determine if this feature has been enabled are in the vendor advisory.
Exploitation requires the attacker to complete a three-way TCP handshake. For this reason the attacker will not be able to spoof the source address of the malicious H.323 packets.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
Administrators are advised to apply the appropriate updates.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems on TCP port 1720.
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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Cisco Multivendor Vulnerability Alerts respond to vulnerabilities identified in third-party vendors' products. These alerts contain information compiled from diverse sources and provide comprehensive technical descriptions, objective analytical assessments, workarounds and practical safeguards, and links to vendor advisories and patches.