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Cache On Delivery — Memcached Opens an Accidental Security Hole

Posted by timothy on from the everything-has-a-downside dept.

jamie spotted this eye-opening presentation (here's a longer explanation) about how easy it is to access sensitive data on many sites using memcached, writing "If you already know what memcached is, skim to slide #17. The jaw-drop will happen around slide #33. Turns out many websites expose their totally-non-protected memcached interface to the Internet, including gowalla, bit.ly, and PBS."

11 of 149 comments (clear)

  1. I fail to see why this is news by OverlordQ · · Score: 5, Insightful

    Much less 'memcached' being at fault. They say it themselves:

    Memcached does not spend much, if any, effort in ensuring its defensibility from random internet connections. So you must not expose memcached directly to the internet, or otherwise any untrusted users.

    All this is is stupid admins doing stupid things story and those are dime a dozen.

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    1. Re:I fail to see why this is news by TheRaven64 · · Score: 5, Insightful

      Which is exactly the point. The default install should never be working-and-insecure. It should be secure, and ideally it should be working. If it is not possible for the default install to be both useful and secure, as appears to be the case with memcached, then it should install only listening on localhost and require explicit intervention by the user to accept connections from other hosts.

      If you can install it and have it work by default, then there is no reason for the user to bother reading the manual, so they won't learn that it needs to be specially configured to be secure. If the default is secure but not particularly useful, then the user needs to explicitly adjust the setting that makes it insecure, and in so doing needs to read the documentation explaining that this will make it insecure and how to mitigate it.

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  2. Re:Let me see if I understand this by Firehed · · Score: 5, Informative

    Memcache's one purpose in life is to be as fast as possible. It makes perfect sense for it to drop the overhead of authentication and leave it on the server operator's head to not make it publicly accessible. It's not rare to strip out MySQL's authentication layer (and presumably the same for other DBs) for a speedup when your DB server is sitting behind a firewall.

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  3. More Boiled and Distilled. by SuperKendall · · Score: 5, Insightful

    Memcache allows anyone to overwrite a cache instance. Seriously? It does not authenticate a write to the cache? And they didn't see this as a problem when desgining memcache? Really?

    Anyone can write on your underwear too, if you are stupid enough to wear it outside your pants.

    Is that an underwear design flaw?

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    1. Re:More Boiled and Distilled. by Farmer+Tim · · Score: 5, Insightful

      Best. Analogy. Ever.

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    2. Re:More Boiled and Distilled. by outsider007 · · Score: 5, Funny

      That's actually more of a feature.

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    3. Re:More Boiled and Distilled. by Farmer+Tim · · Score: 5, Funny

      That's. Why.

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  4. A few clarifications by marcoslaviero · · Score: 5, Informative

    In terms of the vendors identified, Bit.ly, GoWalla and Pbs were notified. Bit.ly and GoWalla repaired the flaws within minutes. I am not aware of Pbs repairing the issue. This talk seems to have struck a chord which I can't really explain (suggestions welcome). Yes, exposing your memcached's is bad (the talk shows just how bad), but it's not a clever find to discover them. [fd: that's my name on the slides]

    1. Re:A few clarifications by marcoslaviero · · Score: 5, Interesting

      There's a deeper issue at play here as it relates to shifting apps and platforms away from your own hardware/networks. Developers are now often responsible for deploying apps onto cloud systems where they don't have experience with network-security or the tools for protecting network-based services, and this is an obvious difference from the traditional network/app split that occurs in most corporates. It doesn't help that memcached (by default) binds to * but they do make this pretty clear (also, remote enumeration of the cache is genuinely a debug feature).

      Man pages help, but when the defaults don't aid developers we need to a rethink both of the software (memcached) and the systems were it's not running securely (cloud platforms).

    2. Re:A few clarifications by IAmGarethAdams · · Score: 5, Funny

      Mostly through rouge employees

      Luckily, they often get caught red-handed.

  5. Admin or distro? by shish · · Score: 5, Interesting

    Debian's default config says:

    # Specify which IP address to listen on. The default is to listen on all IP addresses
    # This parameter is one of the only security measures that memcached has, so make sure
    # it's listening on a firewalled interface.
    -l 127.0.0.1

    Are there any distros that don't have it locked down by default? I would hope not, but if something has it insecure out of the box with no warning that might explain it... (though a good sysadmin would firewall all internal services, whether the documentation tells them to or not)

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