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Avoid using forced OGNL evaluation on untrusted user input, and/or upgrade to Struts 2.5.26 which checks if expression evaluation won't lead to the double evaluation.
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No issues expected when upgrading to Struts 2.5.26
Workaround
Do no not use forced OGNL evaluation in the tag's attributes based on untrusted/unvalidated user input, please follow out recommendations from the Security Guide.
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