Apache Software Foundation released an advisory warning that a patch issued in March for a zero-day vulnerability in Apache Struts did not fully patch the bug. Apparently, the patch for the patch is in development and will be released likely within the next 72 hours.
Rene Gielen of the Apache Struts team said that once the release is available, all Struts 2 users are strongly recommended to update their installations. ASF provided a temporary mitigation that users are urged to apply. On March 2, a patch was made available for a ClassLoader vulnerability in Struts up to version 220.127.116.11. All it took was an attacker to manipulate the ClassLoader via request parameters. However Apache admitted that its fix was insufficient to repair the vulnerability. An attacker exploiting the vulnerability could also cause a denial-of-service condition on a server running Struts 2.
“The default upload mechanism in Apache Struts 2 is based on Commons FileUpload version 1.3 which is vulnerable and allows DoS attacks. Additional ParametersInterceptor allows access to ‘class’ parameter which is directly mapped to getClass() method and allows ClassLoader manipulation.”
It will be the third time that Struts has been updated this year. In February, the Apache Struts team urged developers to upgrade Struts 2-based projects to use a patched version of the Commons FileUpload library to prevent denial-of-service attacks.