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Who should read this
All Struts 2 developers and users
Impact of vulnerability
Possible RCE when performing file upload based on Jakarta Multipart parser
Maximum security rating
Struts 2.3.5 - Struts 2.3.31, Struts 2.5 - Struts 2.5.10
Chris Frohoff <cfrohoff at qualcomm dot com>, Nike Zheng <nike dot zheng at dbappsecurity dot com dot cn>, Alvaro Munoz <alvaro dot munoz at hpe dot com>
It is possible to perform a RCE attack with a malicious
Content-Disposition value or with improper
Content-Length header. If the
Content-Length value is not valid an exception is thrown which is then used to display an error message to a user. This is a different vector for the same vulnerability described in S2-045 (CVE-2017-5638).
If you are using Jakarta based file upload Multipart parser, upgrade to Apache Struts version 2.3.32 or 188.8.131.52.
No backward incompatibility issues are expected.
You can switch to a different implementation of the Multipart parser. We have already prepared two plugins which can be used as a drop-in solution, please find them here. You can use them when you are running the Apache Struts 2.3.8 - 2.5.5 (in case of using the default Jakarta multipart parser) or the Apache Struts 2.3.20 - 2.5.5 (when using an alternative jakarta-stream multipart parser).
Another option is to remove the File Upload Interceptor from the stack, just define your own custom stack and set it as a default - please read How do we configure an Interceptor to be used with every Action. This will work only for Struts 2.5.8 - 2.5.10.