The design of the Hot Standby Routing Protocol (HSRP), as implemented on Cisco IOS 12.1, when using IRPAS, allows remote attackers to cause a denial of service (CPU consumption) via a router with the same IP address as the interface on which HSRP is running, which causes a loop.

Cisco SN 5420 Storage Router 1.1(5) and earlier allows remote attackers to cause a denial of service (halt) via a fragmented packet to the Gigabit interface.

Cisco VPN 3000 Concentrator 2.2.x, and 3.x before 3.5.3, allows remote attackers to cause a denial of service (crash) via a long (1) username or (2) password to the HTML login interface.

HTML interface for Cisco VPN 3000 Concentrator 2.x.x and 3.x.x before 3.0.3(B) allows remote attackers to cause a denial of service (CPU consumption) via a long URL request.

emWEB on Cisco Adaptive Security Appliances (ASA) 5500 series devices with software before 8.2(3) allows remote attackers to cause a denial of service (daemon crash) via a request for a document whose name contains space characters, aka Bug ID CSCsy08416.

The LAN-to-LAN IPSEC capability for Cisco VPN 3000 Concentrator 2.2.x, and 3.x before 3.5.4, allows remote attackers to cause a denial of service via an incoming LAN-to-LAN connection with an existing security association with another device on the remote network, which causes the concentrator to remove the previous connection.

Cisco VPN 3000 Concentrator 2.2.x, 3.6(Rel), and 3.x before 3.5.5, allows remote attackers to cause a denial of service via a long user name.

Cisco ONS15454 and ONS15327 running ONS before 3.4 allows attackers to cause a denial of service (reset to TCC, TCC+, TCCi or XTC) via a malformed HTTP request that does not contain a leading / (slash) character.

Cisco IOS 11.1 through 12.2, when HSRP support is not enabled, allows remote attackers to cause a denial of service (CPU consumption) via randomly sized UDP packets to the Hot Standby Routing Protocol (HSRP) port 1985.

Cisco ONS15454 and ONS15327 running ONS before 3.4 allows attackers to cause a denial of service (reset) via an HTTP request to the TCC, TCC+ or XTC, in which the request contains an invalid CORBA Interoperable Object Reference (IOR).

Cisco SN 5420 Storage Router 1.1(5) and earlier allows remote attackers to cause a denial of service (router crash) via an HTTP request with large headers.

The web management interface for Cisco Content Service Switch (CSS) 11000 switches allows remote attackers to cause a denial of service (soft reset) via (1) an HTTPS POST request, or (2) malformed XML data.

Cisco Unified Personal Communicator 7.0 (1.13056) does not free allocated memory for received data and does not perform validation if memory allocation is successful, causing a remote denial of service condition.

Cisco IOS XR 3.4.0 through 3.9.1, when BGP is enabled, does not properly handle unrecognized transitive attributes, which allows remote attackers to cause a denial of service (peering reset) via a crafted prefix announcement, as demonstrated in the wild in August 2010 with attribute type code 99, aka Bug ID CSCti62211.

Buffer overflows in Cisco Virtual Private Network (VPN) Client 3.5.4 and earlier allows remote attackers to cause a denial of service via (1) an Internet Key Exchange (IKE) with a large Security Parameter Index (SPI) payload, or (2) an IKE packet with a large number of valid payloads.

Memory leak in the Call Telephony Integration (CTI) Framework authentication for Cisco CallManager 3.0 and 3.1 before 3.1(3) allows remote attackers to cause a denial of service (crash and reload) via a series of authentication failures, e.g. via incorrect passwords.

Cisco DSL CPE devices running CBOS 2.4.4 and earlier allows remote attackers to cause a denial of service (hang or memory consumption) via (1) a large packet to the DHCP port, (2) a large packet to the Telnet port, or (3) a flood of large packets to the CPE, which causes the TCP/IP stack to consume large amounts of memory.

Cisco ONS15454 optical transport platform running ONS 3.1.0 to 3.2.0 allows remote attackers to cause a denial of service (reset) by sending IP packets with non-zero Type of Service (TOS) bits to the Timing Control Card (TCC) LAN interface.

Cisco Aironet before 11.21 with Telnet enabled allows remote attackers to cause a denial of service (reboot) via a series of login attempts with invalid usernames and passwords.

Cisco IP Phone (VoIP) models 7910, 7940, and 7960 allow remote attackers to cause a denial of service (crash) via malformed packets as demonstrated by (1) "jolt", (2) "jolt2", (3) "raped", (4) "hping2", (5) "bloop", (6) "bubonic", (7) "mutant", (8) "trash", and (9) "trash2."

Cisco IOS 12.2 and earlier running Cisco Discovery Protocol (CDP) allows remote attackers to cause a denial of service (memory consumption) via a flood of CDP neighbor announcements.

Multiple Cisco networking products allow remote attackers to cause a denial of service on the local network via a series of ARP packets sent to the router's interface that contains a different MAC address for the router, which eventually causes the router to overwrite the MAC address in its ARP table.

Cisco devices IOS 12.0 and earlier allow a remote attacker to cause a crash, or bad route updates, via malformed BGP updates with unrecognized transitive attribute.

Cisco 600 series routers running CBOS 2.0.1 through 2.4.2ap allows remote attackers to cause a denial of service via multiple connections to the router on the (1) HTTP or (2) telnet service, which causes the router to become unresponsive and stop forwarding packets.

Cisco routers and switches running IOS 12.0 through 12.2.1 allows a remote attacker to cause a denial of service via a flood of UDP packets.

Cisco CBOS 2.3.8 and earlier allows remote attackers to cause a denial of service via an ICMP ECHO REQUEST (ping) with the IP Record Route option set.

Web-based configuration utility in Cisco 600 series routers running CBOS 2.0.1 through 2.4.2ap binds itself to port 80 even when web-based configuration services are disabled, which could leave the router open to attack.

Cisco CBOS 2.3.8 and earlier allows remote attackers to cause a denial of service via a series of large ICMP ECHO REPLY (ping) packets, which cause it to enter ROMMON mode and stop forwarding packets.

Cisco IOS 12.1(2)T, 12.1(3)T allow remote attackers to cause a denial of service (reload) via a connection to TCP ports 3100-3999, 5100-5999, 7100-7999 and 10100-10999.

Cisco 12000 with IOS 12.0 and line cards based on Engine 2 and earlier allows remote attackers to cause a denial of service (CPU consumption) by flooding the router with traffic that generates a large number of ICMP Unreachable replies.

PPTP implementation in Cisco IOS 12.1 and 12.2 allows remote attackers to cause a denial of service (crash) via a malformed packet.

Cisco 12000 with IOS 12.0 and line cards based on Engine 2 does not handle the "fragment" keyword in a compiled ACL (Turbo ACL) for packets that are sent to the router, which allows remote attackers to cause a denial of service via a flood of fragments.

Cisco TFTP Server 1.1 allows remote attackers to cause a denial of service (daemon crash) via a crafted (1) read (aka RRQ) or (2) write (aka WRQ) request, or other TFTP packet. NOTE: some of these details are obtained from third party information.

Cisco VPN 3000 series concentrators before 2.5.2(F) allow remote attackers to cause a denial of service via an IP packet with an invalid IP option.

The HTTP server in Cisco IOS 12.0 through 12.1 allows local users to cause a denial of service (crash and reload) via a URL containing a "?/" string.

Cisco 600 routers running CBOS 2.4.1 and earlier allow remote attackers to cause a denial of service via a large ICMP echo (ping) packet.

Unspecified vulnerability in Cisco ASA 5500 Series Adaptive Security Appliance 7.0 before 7.0(8.10), 7.2 before 7.2(4.45), 8.0 before 8.0(5.1), 8.1 before 8.1(2.37), and 8.2 before 8.2(1.15); and Cisco PIX 500 Series Security Appliance; allows remote attackers to cause a denial of service (active IPsec tunnel loss and prevention of new tunnels) via a malformed IKE message through an existing tunnel to UDP port 4500, aka Bug ID CSCtc47782.

CBOS 2.4.1 and earlier in Cisco 600 routers allows remote attackers to cause a denial of service via a slow stream of TCP SYN packets.

Cisco Adaptive Security Appliances (ASA) 5500 series devices with software before 8.2(3) allow remote attackers to cause a denial of service (ASDM syslog outage) via a long URL, aka Bug IDs CSCsm11264 and CSCtb92911.

Buffer overflow in Cisco TACACS+ tac_plus server allows remote attackers to cause a denial of service via a malformed packet with a long length field.

Memory leak in the gk_circuit_info_do_in_acf function in the H.323 implementation in Cisco IOS before 15.0(1)XA allows remote attackers to cause a denial of service (memory consumption) via a large number of calls over a long duration, as demonstrated by InterZone Clear Token (IZCT) test traffic, aka Bug ID CSCsz72535.

Cisco IOS 11.x and 12.x allows remote attackers to cause a denial of service by sending the ENVIRON option to the Telnet daemon before it is ready to accept it, which causes the system to reboot.

Denial of service in Cisco routers running NAT via a PORT command from an FTP client to a Telnet port.

Vulnerability in Cisco 7xx series routers allows a remote attacker to cause a system reload via a TCP connection to the router's TELNET port.

Cisco Catalyst LAN switches running Catalyst 5000 supervisor software allows remote attackers to perform a denial of service by forcing the supervisor module to reload.

Denial of service in Cisco IOS web server allows attackers to reboot the router using a long URL.

Buffer overflow in Cisco 7xx routers through the telnet service.

Attackers can crash a Cisco IOS router or device, provided they can get to an interactive prompt (such as a login). This applies to some IOS 9.x, 10.x, and 11.x releases.

Cisco IOS 12.0 and other versions can be crashed by malicious UDP packets to the syslog port.

A vulnerability in the HTTPS decryption feature of Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. The vulnerability is due to insufficient validation of Secure Sockets Layer (SSL) server certificates. An attacker could exploit this vulnerability by installing a malformed certificate in a web server and sending a request to it through the Cisco WSA. A successful exploit could allow the attacker to cause an unexpected restart of the proxy process on an affected device.