Software Development

The Syslog Hell

Syslog. You’ve probably heard about that, especially if you are into monitoring or security. Syslog is perceived to be the common, unified way that systems can send logs to other systems. Linux supports syslog, many network and security appliances support syslog as a way to share their logs. On the other side, a syslog server is receiving all syslog messages. It sounds great in theory – having a simple, common way to represent logs messages and send them across systems.

Reality can’t be further from that. Syslog is not one thing – there are multiple “standards”, and each of those is implemented incorrectly more often than not. Many vendors have their own way of representing data, and it’s all a big mess.

First, the RFCs. There are two RFCs – RFC3164 (“old” or “BSD” syslog) and RFC5254 (the new variant that obsoletes 3164). RFC3164 is not a standard, while RFC5254 is (mostly).

Those RFCs concern the contents of a syslog message. Then there’s RFC6587 which is about transmitting a syslog message over TCP. It’s also not a standard, but rather “an observation”. Syslog is usually transmitted over UDP, so fitting it into TCP requires some extra considerations. Now add TLS ontop of that as well.

Then there are content formats. RFC5254 defines a key-value structure, but RFC 3164 does not – everything after the syslog header is just a non-structured message string. So many custom formats exist. For example firewall vendors tend to define their own message formats. At least they are often documented (e.g. check WatchGuard and SonicWall), but parsing them requires a lot of custom knowledge about that vendor’s choices. Sometimes the documentation doesn’t fully reflect the reality, though.

Instead of vendor-specific formats, there are also de-facto standards like CEF and the less popular LEEF. They define a structure of the message and are actually syslog-independent (you can write CEF/LEEF to a file). But when syslog is used for transmitting CEF/LEEF, the message should respect RFC3164.

And now comes the “fun” part – incorrect implementations. Many vendors don’t really respect those documents. They come up with their own variations of even the simplest things like a syslog header. Date formats are all over the place, hosts are sometimes missing, priority is sometimes missing, non-host identifiers are used in place of hosts, colons are placed frivolously.

Parsing all of that mess is extremely “hacky”, with tons of regexes trying to account for all vendor quirks. I’m working on a SIEM, and our collector is open source – you can check our syslog package. Some vendor-specific parsers are yet missing, but we are adding new ones constantly. The date formats in the CEF parser tell a good story.

If it were just two RFCs with one de-facto message format standard for one of them and a few option for TCP/UDP transmission, that would be fine. But what makes things hell is the fact that too many vendors decided not to care about what is in the RFCs, they decided that “hey, putting a year there is just fine” even though the RFC says “no”, that they don’t really need to set a host in the header, and that they didn’t really need to implement anything new after their initial legacy stuff was created.

Too many vendors (of various security and non-security software) came up with their own way of essentially representing key-value pairs, too many vendors thought their date format is the right one, too many vendors didn’t take the time to upgrade their logging facility in the past 12 years.

Unfortunately that’s representative of our industry (yes, xkcd). Someone somewhere stitches something together and then decades later we have an incomprehensible patchwork of stringly-typed, randomly formatted stuff flying around whatever socket it finds suitable. And it’s never the right time and the right priority to clean things up, to get up to date, to align with others in the field. We, as an industry (both security and IT in general) are creating a mess out of everything. Yes, the world is complex, and technology is complex as well. Our job is to make it all palpable, abstracted away, simplified and standardized. And we are doing the opposite.

Published on Java Code Geeks with permission by Bozhidar Bozhanov, partner at our JCG program. See the original article here: The Syslog Hell

Opinions expressed by Java Code Geeks contributors are their own.

Bozhidar Bozhanov

Senior Java developer, one of the top stackoverflow users, fluent with Java and Java technology stacks - Spring, JPA, JavaEE, as well as Android, Scala and any framework you throw at him. creator of Computoser - an algorithmic music composer. Worked on telecom projects, e-government and large-scale online recruitment and navigation platforms.
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