Invalid URI in request and apache stopps working

Question

Today our apache stopped working, he did not crash but stopped to response.

The only error i can see in the error_log is this:

[Thu Feb 11 10:00:05.245233 2016] [core:error] [pid 7496] [client 169.229.3.91:54481] 
AH00126: Invalid URI in request 2p[\x96(\xc0\xf6\xb6w\x89\xf2=\xcd\x8f\xa4i\x9c\xb6\xec<n\v\x11!W\xdc\x9f\x1c\xdd8?\xb4\xe0\xb6,eW\xf0K\xa0H\xd1-\x91\x9f

accesslog contains the same

linux-9jgs:/home/USER # cat /var/log/apache2/access_log |grep 169.229.3.91
169.229.3.91 - - [11/Feb/2016:10:00:05 +0100] "2p[\x96(\xc0\xf6\xb6w\x89\xf2=\xcd\x8f\xa4i\x9c\xb6\xec<n\v\x11!W\xdc\x9f\x1c\xdd8?\xb4\xe0\xb6,eW\xf0K\xa0H\xd1-\x91\x9f" 307 264 "-" "-"
linux-9jgs:/home/USER #

any idea how we can prevent apache from hang-up next time?

We are using this version:

Server version: Apache/2.4.10 (Linux/SUSE)
Server built:   2015-08-11 15:51:30.000000000 +0000
Server's Module Magic Number: 20120211:36
Server loaded:  APR 1.5.1, APR-UTIL 1.5.3
Compiled using: APR 1.5.1, APR-UTIL 1.5.3
Architecture:   64-bit
Server MPM:     prefork
  threaded:     no
    forked:     yes (variable process count)

Answer 1

I would consider

• Upgrading to Apache webserver latest version (2.4.18 at time of writing)
• Reviewing security-related settings
• Use of modules such as mod_security

See Secure Your Apache With mod_security

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Another action that might be worth trying would be to change the MPM from prefork to worker in the hope that it might be less vulnerable to this problem.

See How do I select which Apache MPM to use? and Understanding Apache 2 MPM (worker vs prefork)