Load Balanced DNS with dnsdist

In recent weeks I’ve found the need to configure and deploy a proper load balancing solution for an authoritative DNS cluster. Now for most solutions (up to a certain scale, and you’d know if you were there) a single-purpose authoritative DNS resolver doesn’t really need a balancing frontend; you can reasonably expect a decent-sized box running a modern kernel to handle several hundred thousand UDP packets per second, with a minimal amount of complimentary TCP traffic. Putting a frontend load balancing tier in front of an authoritative DNS cluster is really only necessary when either hardware redundancy or significant traffic shaping is a requirement, or the generation of authoritative data is expensive and needs to be horizontally scalable. I found myself needing to satisfy a few of these conditions, and have had a wonderful time playing and poking at a purpose-built FOSS DNS load balancing solution in dnsdist.

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Benchmarking Simple String Comparison Options for OpenResty

Perhaps one of the most powerful primatives that lua-nginx-module provides out of the box is a sane, simple wrapper for regular expression operations (via PCRE). String matching, replacing (and now splitting!) via regex allows for much greater flexibility in string processing than Lua’s native string library. Recently while cleaning up an OpenResty InfluxDB client I needed to do some simple string comparison. My knee-jerk reaction was to use a simple expression in ngx.re.find, but I had a hunch that the overhead of using the PCRE lib would be a waste, and that native Lua pattern searches would be quicker. Time for a benchmark to figure out the most sane solution!

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Properly Scoping lua-nginx-module’s ngx.ctx

Some time ago I wrote a comparison of lua-nginx-module’s per-request context table and per-worker shared memory dictionaries. Silly me- our examination of the usage of hitting ngx.ctx is pretty naive. Of course, constantly doing the magic lookup to get to the table will be expensive. What happens when we localize the table, do our work, and shove it back into the ngx API at the end of our handler?

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Mod_Security JSON Audit Logs, Revisited

Last year I took a look at generating Mod_Security audit logs as JSON data, rather than the module’s native format (which is… err… difficult to parse). My initial approach was incomplete, needlessly introduced additional dependencies, and leaked like a sieve; I ended up abandoning this to work on FreeWAF. Some new use uses came up that would benefit from more structured Mod_Security audit logs, so I’ve revamped a patch to emit JSON data using a more sane approach.

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FreeWAF Updates and New Features

January tends to be a pretty quiet month in the admin/operations world. Most people are still coming back from holiday, new yearly plans are being made, meetings are held, and the server monkeys… sit and watch the graphs scroll by. The rest of the world’s gradual return to work means the start of a seasonal upswing, but we’re still in a relatively low point, so that generally means a light workload. That extra free time has given me a chance to put in a good chunk of work towards FreeWAF, cleaning up code, adding new features, and interacting with a total stranger (score!). I’ve just tagged a new release, v0.4, which provides a handful of new features that were sorely missing:

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Fancybox for WordPress – Zero Day and Broken Patch

A malicious iframe has been making its rounds due to a broken non-existent security check in the admin section of the Fancybox for WordPress plugin. Samples of affected sites indicate the vulnerability is being used to initiate a drive-by download targeting MSIE browsers (potentially targeting a recently-announced unpatched IE exploit?). The plugin exploit vector results from poor handling of unauthenticated requests to the plugin’s admin options page (taken from fancybox.php):

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