LIBRELP 1.7.0 release upcoming

Librelp 1.7 brings some memory leaks fixes, support for chained certificate files and a bit more. The official release is tomorrow. It will be co-released with rsyslog 8.2008.

Librelp Logo Image
LIBRELP is a library for reliable network event logging. (Image: Rainer Gerhards)

The memory leak is especially relevant for some load-balancers, including AWS. I highly recommend to use the new library in such environments. As a side-note, we have also finally done some library symbol cleanups. If you used non-API functions that will hurt you. However, to the best of my knowledge nobody does such dirty tricks.

Adiscon will also integrate the new librelp in to it’s Windows products (including WinSyslog and EventReporter)


Librelp is library for reliable network event logging, It provides syslog-like functionality with a drastically reduced risk of messages loss. Note that industry-standard TCP syslog is unreliable by design. Librelp was written to address these shortcomings.

Rainer Gerhards initiated the librelp open source project. It is primarily sponsored by Adiscon.

How we found and fixed a CVE in librelp

This is a joint blog post, from Adiscon and Semmle, about the finding and fixing of CVE-2018-1000140, a security vulnerability in librelp. This was a collaborative effort by:

  • Kevin Backhouse, Semmle, Security Researcher.
  • Rainer Gerhards, Adiscon, Founder and President.
  • Bas van Schaik, Semmle, Head of Product.

We have published this post on Rainer’s blog here and the LGTM blog.

Bas originally found the vulnerability (using and Rainer fixed it. Kev developed the proof-of-concept exploit.

In this blog post, we explain the cause of the bug, which is related to a subtle gotcha in the behavior of snprintf, and how it was found by a default query on We also demonstrate a working exploit (in a docker container, so that you can safely download it and try it for yourself). As a bonus, we give a short tutorial on how to set up rsyslog with TLS for secure communication between the client and server. Continue reading “How we found and fixed a CVE in librelp”

recent librelp development

I thought I share some news on what I have been busy with and intend to be in the future. In the past days, I have added more config options to librelp, which now supports GnuTLS compression methods as well as provides the ability to set the Diffie-Hellman key strength (number of bits) and – for experts – to set the GnuTLS priorities, which select the cipher methods and other important aspects of TLS handling.

This is done now and I also added rsyslog facilities to use these new features. Some of this stuff is not yet released, but will soon be.

The next big step is preventing man-in-the-middle attacks. I will most probably use SSH-type fingerprint authentication, so that no full PKI is necessary to make this work. I guess implementing this feature set will probably take a couple of days and will keep you posted on how things progress.

TLS for librelp

If you followed librelp’s git, you have probably already noticed that there is increased activity. This is due to the fact that TLS support is finally being added! Thanks to some unnamed sponsor, we could invest “a bit” of time to make this happen.

We have decided to base TLS support on GnuTLS, which has matured very much, is preferred by Debian and fully supported by Red Hat and has no licensing issues with GPL like openssl has (plus the sponsor also preferred it). We build TLS support directly into librelp, as we assume it will get very popular, so an abstraction layer would not make that much sense, especially given the fact the GnuTLS nowadays is almost already installed by default. And remember that an abstraction layer always adds code complexity and an (albeit limited) runtime overhead.

Librelp 1.1.0 will be the first version with basic TLS support. With “basic”, we mean that this is a full TLS implementation, but there are some useful additional features not yet present. Most importantly, this version will not support certifiates but rather work with anonymous Diffie-Hellmann key exchange. This means that while the integrity and privacy of the session can be guaranteed as far as the network is concerned, this version does not guard against man-in-the-middle attacks. The reason simply is that there is no way to mutually authenticate peers without certificates. We still think it makes a lot of sense to release that version, as it greatly improves the situation.

Obviously, we have plans to add certificate support in the very near future. And this also means we will add ways for mutual authentication, much like in rsyslog’s RFC 5425 implementation. It’s not finally decided if we will support all authentication options RFC 5425 offers (some may not be very relevant in practice), but that’s so far undecided. We currently strongly consider to start with fingerprint-based authentication, as this permits the ability to do mutual authentication without the need to setup a full-blown PKI. Also, most folks know fingerprint authentication: this is what ssh does when it connects to a remote machine.

So stay tuned to librelp development, many more exciting things are coming up. Please note that rsyslog 7.5.0 will be the first version to utilize the new librelp features – but that’s something for a different blog posting.

[This is also cross-posted to the librelp site]