LibGD.
Upgrade the PHP version.
Upgrade the 7.0.x series to 7.0.6 or later.Upgrade the 5.6.x series to 5.6.21 or later.Upgrade the 5.5.x series to 5.5.35 or later.
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Fix
Use Alibaba Cloud Security Web Application Firewall to intercept the attacking code for this vulnerability.
Upgrade Struts to version 2.5 or later versions from the official website.
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