Summary
A regular expression Denial of Service when using URLValidator (similar to S2-044 & S2-047)Who should read this | All Struts 2 developers and users |
|---|---|
Impact of vulnerability | Possible DoS attack when using URLValidator |
Maximum security rating | Low |
Recommendation | Upgrade to Struts 2.5.13 or Struts 2.3.34 |
Affected Software | Struts 2.3.7 - Struts 2.3.33, Struts 2.5 - Struts 2.5.12 |
Reporter | Adam Cazzolla <acazzolla at sonatype dot com>, Jonathan Bullock <jonbullock at gmail dot com> |
CVE Identifier | CVE-2017-9804 |
Problem
The previous fix issued with S2-047 was incomplete. If an application allows enter an URL in a form field and built-in URLValidator is used, it is possible to prepare a special URL which will be used to overload server process when performing validation of the URL.
Solution
Upgrade to Apache Struts version 2.5.13 or 2.3.34.
Backward compatibility
No backward incompatibility issues are expected.
Workaround
Instead of using the default RegEx provided by the UrlValidator you can use the below one:
"^(?:https?|ftp):\\/\\/" +
"(?:(?:[a-z0-9$_.+!*'(),;?&=\\-]|%[0-9a-f]{2})+" +
"(?::(?:[a-z0-9$_.+!*'(),;?&=\\-]|%[0-9a-f]{2})+)?" +
"@)?#?" +
"(?:(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)*" +
"[a-z][a-z0-9-]*[a-z0-9]" +
"|(?:(?:[1-9]?\\d|1\\d{2}|2[0-4]\\d|25[0-5])\\.){3}" +
"(?:[1-9]?\\d|1\\d{2}|2[0-4]\\d|25[0-5])" +
")(?::\\d+)?" +
")(?:(?:\\/(?:[a-z0-9$_.+!*'(),;:@&=\\-]|%[0-9a-f]{2})*)*" +
"(?:\\?(?:[a-z0-9$_.+!*'(),;:@&=\\-\\/:]|%[0-9a-f]{2})*)?)?" +
"(?:#(?:[a-z0-9$_.+!*'(),;:@&=\\-]|%[0-9a-f]{2})*)?" +
"$"