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  • S2-050
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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



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


Adam Cazzolla <acazzolla at sonatype dot com>, Jonathan Bullock <jonbullock at gmail dot com>

CVE Identifier



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.


Upgrade to Apache Struts version 2.5.13 or 2.3.34.

Backward compatibility

No backward incompatibility issues are expected.


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})*)?" +



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