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Cisco has released eight security updates for the software used to power its routers, but has refused to confirm reports that it is working on a patch for a major TCP/IP bug.

The patches for the Internetwork Operating System (IOS) software were released Wednesday. None of the bugs had been publicly disclosed ahead of Wednesday's updates, but some of them were reported to Cisco by outside sources.

The eight updates fix 11 security vulnerabilities, according to Jean Reese, senior manager with Cisco's Product Security Incident Response Team.

Most of the bugs could be exploited by attackers to crash or somehow disrupt service to a router, typically if a specific, vulnerable service is enabled, Cisco said.

For example, Cisco has fixed two bugs in its SSLVPN (Secure Sockets Layer Virtual Private Network) software that could be used to crash the device. Attackers could exploit one of these bugs by sending a specially crafted HTTPS packet to the router. The bug does not affect users of the company's ASA 5500 appliance or of Cisco IOS XR or XE software, however.

SSLVPN lets users outside of the corporate firewall access their company's network using a web browser, instead of installing special VPN software on their PC.

Another serious bug affects those who have enabled the Secure Copy Protocol (SCP), used to allow file transfers over the network. Because of this bug, an authenticated user on the device could "transfer files to and from a Cisco IOS device that is configured to be an SCP server, regardless of what users are authorised to do," Cisco said in its advisory. This could allow a user to mess with the router's configuration files or sneak a peek at passwords, Cisco said. This bug was reported to Cisco by Kevin Graham, the company said.

For the bug to be exploited, the Cisco user would need to have a command line interface (CLI) on the router. "The SCP bug is pretty bad if you have read-only CLI users," said Felix Lindner, a noted Cisco expert who is head of Recurity Labs, in an email interview. "If you are a read-only CLI user and this bug allows you to write the configuration or, even worse, a new backdoored IOS image. That's evil."

According to sources familiar with the matter, Cisco and other vendors have been working on patching a major TCP/IP bug in its routers that could be exploited in what's called a Sockstress attack. This flaw, which has not been disclosed publicly, could be used to take down a router using a very low-bandwidth denial of service attack.

Reese wouldn't comment on whether this bug was patched in Wednesday's updates. The company did not credit the two researchers who first discussed the Sockstress attack in any of its updates, a sign that the issue may not have been patched.

More details on the updates can be found here.

Cisco's next set of IOS patches is due 23 September.

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