Hey Paul, this is a very interesting article. We’ve collected 2 other reports of zlib crashing in memcpy() over the last few months and are still a bit in the fog for now, especially since libslz seems to fix the issue for you. I tend to trust zlib as being stable, so probably it’s zlib’s integration into haproxy that is causing trouble (but why now as it’s been working fine for years?). Are you using “maxzlibmem” in your global section ? The only candidate I’m thinking about could be this one, indicating a failure to properly recover from an out-of-memory condition.