It’s been a few weeks since [Dan Kaminsky] announced the nature of the DNS vulnerability and allowed 30 days of non-disclosure for patches to be applied before details of the exploit went public. Unfortunately, the details were leaked early and it didn’t take long for a functional exploit to be released into the wild. Since then, many ISPs have taken steps to prevent their users from falling victim to the attack, and BIND, the widely-used DNS protocol implementation, was updated to minimize the threat. Even then, there were reports of a version of the attack being actively used on AT&T’s DNS servers.
Mac OSX uses a BIND implementation but as of yet, Apple has not released a patch updating the system (Microsoft, on the other hand, patched this up on July 8). As a result, machines running OSX are at risk of being exploited. Individual users are less likely to be targeted, since the attacks are directed towards servers, but it’s not a smart idea to leave this vulnerability open. [Glenn Fleishman] has published a way to update BIND on OSX manually, rather than waiting on Apple to patch it themselves. It requires Xcode and a bit of terminal work, but it’s a relatively painless update. When we tried it, the “make test” step skipped a few tests and told us to run “bin/tests/system/ifconfig.sh up”. That allowed us to re-run the tests and continue the update without further interruption. [Fleischman] warns that people who manually update BIND may break the official update, but he will update his instructions when it happens with any possible workarounds. Unfortunately, this fix only works for 10.5 but alternative, yet less effective methods may work for 10.4 and earlier.
If you’d like to know if your preferred DNS servers are vulnerable or not, you can use the DNS checker tool from Doxpara. As an alternative to your ISP’s DNS servers, you can use OpenDNS, which many prefer for its security features and configuration options.
UPDATE: Full audio of the webcast is now available
Today Black Hat held a preview webcast with [Dan Kaminsky] about the massive DNS bug he discovered. On July 8th, multiple vendors announced a patch for an undisclosed DNS vulnerability. [Dan Kaminisky] did not release the details of the vulnerability at that time, but encouraged security researchers to not release their work, if they did happen to discover the bug. On the 21st, the full description of the vulnerability was leaked.
In today’s webcast, [Dan] covered how he felt about the handling of the vulnerability and answered a few questions about it. He started out by talking about how he stumbled across the bug; he was working on how to make content distribution faster by using DNS to find the server closest to the client. The new attack works because DNS servers not using port randomization make it easy for the attacker to forge a response. You can read the specifics of the attack here.
Continue reading “DNS cache poisoning webcast”
We’ve been tracking Metasploit commits since Matasano’s premature publication of [Dan Kaminsky]’s DNS cache poisoning flaw on Monday knowing full well that a functional exploit would be coming soon. Only two hours ago [HD Moore] and [I)ruid] added a module to the Metasploit Project that will let anyone test the vulnerability (with comment: “ZOMG. What is this? >:-)“). [HD] told Threat Level that it doesn’t work yet for domains that are already cached by the DNS server, but it will automatically wait for the cached entry to expire and then complete the attack. You can read more about the bailiwicked_host.rb module in CAU’s advisory. For a more detailed description of how the attack works, see this mirror of Matason’s post. You can check if the DNS server you are using is vulnerable by using the tool on [Dan]’s site.
The Zlob trojan, also known as DNSChanger, has been around for a few years, but recent Zlob variants to appear in the wild attempt to log into routers using a list of default admin/password combos. If they succeed, they alter the DNS records on the router to reroute traffic through the attacker’s server.
Our friend [Dan Kaminisky] recently did a presentation warning against vulnerabilities in internet browser plugins that allow attackers to mount DNS rebinding attacks against routers with default passwords.. Though it achieves the same end, Zlob is different because it infects by the tried-and-true method of fooling users into downloading it inside a fake video codec. Once it is running on a client machine, it is free to attempt to use the default admin id and password of the router to log in and alter DNS settings. It even supports the DD-WRT firmware.
Even if a system is wiped clean of Zlob trojans, the router could still be compromised. The good news is that it is easy to fix and even easier to prevent. Fixing it takes no more than wiping all network clients clean, then resetting the router and restoring custom settings. Prevention is a simple matter of changing the router’s password.
[IronGeek] has published his latest video how-to: DNS Spoofing with Ettercap. Ettercap is designed specifically to perform man in the middle attacks on your local network. It can do ARP poisoning, collect passwords, fingerprint OSes, and content filtering. For DNS spoofing, you just need to edit a config file that defines which domains resolve to which IP addresses. You can use wildcards for the domains. In the video, he uses Linux because the network interfaces are easier to remember. Once you’re done playing with DNS spoofing, remember to flush your local cache otherwise your browser will continue to go to the wrong IP.
Charter Communications seems to be pulling some sort of crap with their DNS servers. While working on a new project our friend Billy Hoffman, discovered that Charter was reporting absolutely every domain as resolving. They do offer a solution by providing an opt-out cookie, which isn’t useful at all if you’re not using a web browser… and I’m guessing most of Charter’s subscribers aren’t looking for a bastardized version of the net. We’ve seen recently that messing with DNS like this can actually open up new security holes.