CVE-2021-31805 RCE bug in Apache Struts was finally patched

Apache addressed a critical flaw in Apache Struts RCE that was linked to a previous issue that was not properly fixed.

Apache Struts is an open-source web application framework for developing Java EE web applications.

The Apache Software Foundation urges organizations to address a vulnerability, tracked as CVE-2021-31805, affecting Struts versions ranging 2.0.0 to 2.5.29. An attacker could trigger this vulnerability to take control of an affected system.

According to the advisory published by Apache, the issue addressed by the organization is a critical flaw in Apache Struts linked to a previous OGNL Injection flaw (CVE-2020-17530) that wasn’t properly fixed.

The remote code execution flaw, tracked as CVE-2020-17530, resides in forced OGNL evaluation when evaluated on raw user input in tag attributes.

“Forced OGNL evaluation, when evaluated on raw user input in tag attributes, may lead to remote code execution – similar to S2-059.” reads the advisory published by the Apache Software Foundation. “Some of the tag’s attributes could perform a double evaluation if a developer applied forced OGNL evaluation by using the %{...} syntax. Using forced OGNL evaluation on untrusted user input can lead to a Remote Code Execution and security degradation.”

Upon forcing OGNL evaluation using the %{…} syntax, tag’s attributes could perform double evaluation. Forced OGNL evaluation on untrusted input it is possible to achieve remote code execution.

“The fix issued for CVE-2020-17530 (S2-061) was incomplete. Still some of the tag’s attributes could perform a double evaluation if a developer applied forced OGNL evaluation by using the %{…} syntax. Using forced OGNL evaluation on untrusted user input can lead to a Remote Code Execution and security degradation.” reads the advisory published by Apache.

CISA also published a security advisory for Struts 2 recommending organizations to upgrade their installs.

Apache advisory recommends avoiding using forced OGNL evaluation on untrusted user input, and/or upgrade to Struts 2.5.30 or greater which checks if expression evaluation won’t lead to the double evaluation.

Please vote for Security Affairs as the best European Cybersecurity Blogger Awards 2022 – VOTE FOR YOUR WINNERS
Vote for me in the sections “The Underdogs – Best Personal (non-commercial) Security Blog” and “The Tech Whizz – Best Technical Blog” and others of your choice.
To nominate, please visit: https://docs.google.com/forms/d/e/1FAIpQLSfxxrxICiMZ9QM9iiPuMQIC-IoM-NpQMOsFZnJXrBQRYJGCOw/viewform

Follow me on Twitter: @securityaffairs and Facebook

[adrotate banner=”9″]

[adrotate banner=”12″]

Pierluigi Paganini

(SecurityAffairs – hacking, Apache)

[adrotate banner=”5″]

[adrotate banner=”13″]

Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.