Cisco Systems has fixed four denial-of-service vulnerabilities that attackers could exploit to cause Web Security Appliance devices to stop processing traffic correctly.The Cisco Web Security Appliance (WSA) is a line of security devices that inspect Web traffic going in and out of an organization in order to detect malware, prevent data leaks, and enforce Internet access policies for users and applications. The devices run an operating system called Cisco AsyncOS.One of the four DoS vulnerabilities fixed Wednesday by Cisco stems from how the OS handles a specific HTTP response code. An attacker could send a specifically crafted HTTP request in order to consume the entire memory of an affected device.If this happens, the device will no longer accept new incoming connection requests, Cisco said in an advisory.All Cisco AsyncOS versions older than 9.0.1-162 are affected. Users are advised to upgrade to this version. Version 9.1 is also unaffected.Another DoS vulnerability is caused by a lack of proper input validation of the packets that make up HTTP POST requests. The flaw can be exploited through specifically crafted HTTP requests and can lead to the proxy process becoming unresponsive and the WSA reloading.Only AsyncOS version 8.0 is affected by this vulnerability. Users can upgrade to 8.0.6-119 or 9.0.1-162, which contains patches for all four flaws, Cisco said in an advisory.The third vulnerability stems from a failure to free memory when a file range for cached content is requested through the WSA. By opening multiple connections and requesting file ranges, an attacker can cause the WSA to run out of memory and stop passing traffic.Versions 8.5 to 8.8 of AsyncOS are affected and Cisco recommends upgrading to 9.0.1-162.The fourth vulnerability occurs because AsyncOS does not properly allocate space for the HTTP header and an expected HTTP payload. Exploiting this flaw can cause the proxy process to reload and the traffic to be stopped.The flaw affects AsyncOS versions 8.8 and lower. Cisco has fixed the flaw in versions 8.5.3-069 for the 8.5 branch and 9.0.1-162.In addition to the WSA flaws, Cisco also patched a moderate severity cross-site scripting vulnerability in the Web interface of the Cisco Unified Computing System (UCS) Central Software.