IBM WebSphere deserialization of untrusted data
Advisory url: http://lab.mediaservice.net/advisory/2016-02-websphere.txt
Security Advisory @ Mediaservice.net Srl
(#02, 07/10/2016) Data Security Division
Title: IBM WebSphere deserialization of untrusted data
Application: IBM WebSphere 7,8,8.5,9
Description: The application server deserializes unstrusted data when the
WASPostParam cookie is present. This can lead to a DoS via
resource exhaustion and potentially remote code execution.
Authors: Federico Dotta <federico.dotta@mediaservice.net>
Maurizio Agazzini <inode@mediaservice.net>
Vendor Status: Fixed (PI62375)
CVE Candidate: The Common Vulnerabilities and Exposures project has assigned
the name CVE-2016-5983 to this issue.
References: http://lab.mediaservice.net/advisory/2016-02-websphere.txt
http://lab.mediaservice.net/code/websphere_payload.zip
http://www-01.ibm.com/support/docview.wss?uid=swg21990060
1. Abstract.
When using custom form authentication, IBM WebSphere automatically sets the
cookies WASPostParam and WASReqURL when the LtpaToken2 session cookie is
invalid. The data contained in these cookies is used when the user logs in
again to retrieve the last visited page and related parameters.
The WASPostParam is a serialized Java object that is deserialized without
checking the object type. This behavior can be exploited to cause a denial of
service and potentially execute arbitrary code.
The objects that can cause the DoS are based on known disclosed payloads
taken from:
- https://gist.github.com/coekie/a27cc406fc9f3dc7a70d
Currently there is no known chain that allows code execution on IBM WebSphere,
however new chains are discovered every day.
2. Example Attack Session.
The attack can be reproduced as follows:
- create an application with custom form authentication
- after user login, the LtpaToken2 is set by the application server
- make a HTTP GET request that contains the WASPostParam cookie with one of
these contents:
* 01_BigString_limited_base64.txt: it's a string object; the server will
reply in a normal way (object size similar to the next one).
* 02_SerialDOS_limited_base64.txt: the application server will require
about 2 minutes to execute the request with 100% CPU usage.
* 03_BigString_base64.txt it's a string object; the server will
reply in a normal way (object size similar to the next one).
* 04_SerialDOS_base64.txt: the application server will require an
unknown amount of time to execute the request with 100% CPU usage.
3. Affected Platforms.
This vulnerability affects the following versions and releases of
IBM WebSphere Application Server and priors versions:
- Liberty 16.0.0.2
- 9.0.0.1
- 8.5.5.10
- 8.0.0.12
- 7.0.0.41
4. Fix.
Apply Interim Fix PI62375
http://www-01.ibm.com/support/docview.wss?uid=swg24042712
5. Proof Of Concept.
See websphere_payload.zip and Example Attack Session above.
6. Timeline
20/08/2016 - First communication sent to IBM PSIRT (psirt at us.ibm.com)
22/08/2016 - IBM Response, PSIRT Advisory 6345 assigned to the bug
05/10/2016 - Communication from IBM with fix information (PI62375)
07/10/2016 - Security Advisory released
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