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Category:   Application (Generic)  >   Splunk Vendors:   Splunk Inc.
(Splunk Issues Fix) Python Hash Table Collision Bug Lets Remote Users Deny Service
SecurityTracker Alert ID:  1027720
SecurityTracker URL:
CVE Reference:   CVE-2012-1150   (Links to External Site)
Date:  Nov 5 2012
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): prior to 5.0
Description:   A vulnerability was reported in Python. A remote user can cause denial of service conditions. Splunk is affected.

A remote user can send specially crafted POST request values to trigger hash collisions and cause significant performance degradation on the target server.

The original advisory is available at:

Alexander Klink of n.runs AG and Julian Walde of Technische Universitat Darmstadt reported this vulnerability. Scott A. Crosby and Dan S. Wallach of Rice University reported the theoretical attack.

Impact:   A remote user can cause performance to degrade on the target server.
Solution:   Splunk has issued a fix (5.0).

The Splunk advisory is available at:

Cause:   Randomization error
Underlying OS:  Linux (Any), UNIX (AIX), UNIX (FreeBSD), UNIX (HP/UX), UNIX (macOS/OS X), UNIX (Solaris - SunOS), Windows (Any)

Message History:   This archive entry is a follow-up to the message listed below.
Dec 29 2011 Python Hash Table Collision Bug Lets Remote Users Deny Service

 Source Message Contents

Subject:  [Full-disclosure] n.runs-SA-2012.003 - SPLUNK DoS HashDOS

n.runs AG                              security(at)
n.runs-SA-2012.003                                           02-Nov-2012
Vendors:            Splunk Inc.,
Product:            Splunk 4.3.x (+ possibly earlier versions)
Vulnerability:      Unauth. remote denial of service against splunkweb
Tracking IDs:       CVE-2012-1150
Vendor communication:
2012/09/03 Reported the issue via Splunk's website
2012/09/04 Splunk responds and assigns tracking ID, plans fix for 5.0.
                       Replacing the Python version in a maintenance release
	       was considered too risky.
2012/10/25 Splunk informs us that 5.0 will be available on November 1st.
2012/10/29 Splunk 5.0 is released.

Splunkweb uses Python 2.7.2, which suffers from a vulnerability which allows
attacker to produce hash collisions for the hash table string hashing
This leads to an O(n^2) complexity when inserting n keys (see


An attacker can abuse this vulnerability by sending a POST request to
(for example to the login form endpoint) with colliding keys. Even a
amount of POST data leads to a 100% CPU usage for the splunkweb process.


Denial of service (CPU exhaustion) against the Splunk server.


This issue has been fixed in Splunk 5.0 by updating the Python version
to 2.7.3 and enabling hash randomization.  =

Alexander Klink, n.runs AG (discovery)
This advisory and upcoming advisories:
About n.runs:
n.runs AG is a vendor-independent consulting company specialising in the
areas of: IT Infrastructure, IT Security and IT Business Consulting.

Copyright Notice:
Unaltered electronic reproduction of this advisory is permitted. For all
other reproduction or publication, in printing or otherwise, contact for permission. Use of the advisory constitutes
acceptance for use in an =93as is=94 condition. All warranties are excluded.
In no event shall n.runs be liable for any damages whatsoever including
direct, indirect, incidental, consequential, loss of business profits or
special damages, even if n.runs has been advised of the possibility of such
Copyright 2012 n.runs AG. All rights reserved. Terms of use apply.

Full-Disclosure - We believe in it.
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