A vulnerability in the cut-through proxy function of Cisco Firewall Services Module (FWSM)
Software could allow an unauthenticated, remote attacker to cause a
reload of the affected system.
The vulnerability is due to a race
condition when releasing the memory allocated by the cut-through proxy function. An attacker could exploit this vulnerability by sending
traffic to match the condition that triggers cut-through proxy authentication. An exploit could allow the attacker to
trigger a reload of the affected system. Repeated exploitation could result in a denial of service (DoS) condition.
Cisco has confirmed the vulnerability in a security advisory and has released software updates.
Indicators of Compromise
Cisco Firewall Services Module versions 3.1, 3.2, 4.0, and 4.1 are affected.
The vulnerability is due to a race condition when releasing the memory allocated by the cut-through proxy function of the Cisco FWSM.
An unauthenticated, remote attacker could exploit this vulnerability by sending IPv4 traffic crafted to match the condition that triggers cut-through proxy authentication to a targeted device. When the device processes the malicious traffic, the attacker could cause the device to reload abnormally. Repeated exploitation could cause a DoS condition for legitimate users.
To exploit this vulnerability, an attacker may require access to trusted, internal networks to send crafted requests to the affected software. This access requirement could limit the likelihood of a successful exploit.
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 are advised to allow only trusted users to have network access.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to monitor affected systems.
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 email 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.