CVE-2017-4971 in Spring Web Flow
Summary
by MITRE
An issue was discovered in Pivotal Spring Web Flow through 2.4.4. Applications that do not change the value of the MvcViewFactoryCreator useSpringBinding property which is disabled by default (i.e., set to 'false') can be vulnerable to malicious EL expressions in view states that process form submissions but do not have a sub-element to declare explicit data binding property mappings.
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Analysis
by VulDB Data Team • 10/20/2019
The vulnerability described in CVE-2017-4971 represents a critical server-side template injection flaw within the Pivotal Spring Web Flow framework version 2.4.4 and earlier. This vulnerability specifically affects applications that rely on the default configuration of MvcViewFactoryCreator with the useSpringBinding property set to false, creating an exploitable condition where malicious expression language expressions can be executed within view states that handle form submissions. The flaw resides in the framework's handling of user input within view state definitions, particularly when applications do not explicitly declare data binding property mappings through sub-elements. This default configuration creates a dangerous execution environment where untrusted input can be processed through the expression language engine without proper sanitization or validation.
The technical implementation of this vulnerability leverages the Spring Web Flow's view state processing mechanism, where form submission data is typically bound to model objects through the framework's data binding capabilities. When the useSpringBinding property remains disabled, the framework falls back to processing expressions through the Expression Language (EL) engine, which can interpret and execute malicious expressions embedded within view state parameters. Attackers can craft form submissions containing specially crafted EL expressions that, when processed by the vulnerable framework, can execute arbitrary code on the server. This occurs because the framework's default behavior does not properly sanitize or restrict expression evaluation in contexts where user input is processed without explicit binding declarations, creating a path for remote code execution through carefully constructed payload data.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass full system compromise and data exfiltration capabilities. An attacker exploiting this vulnerability can execute arbitrary commands on the affected server, potentially gaining access to sensitive data, escalating privileges, or deploying additional malicious payloads. The vulnerability affects applications that process user input through form submissions in view states without explicit data binding declarations, making it particularly dangerous in web applications that handle user-generated content or form data. The default configuration of the framework means that many applications may be vulnerable without explicit security hardening, creating a widespread risk across Spring Web Flow implementations. This vulnerability directly aligns with CWE-94, which describes improper control of generation of code, and represents a classic server-side template injection attack vector that can lead to complete system compromise.
Organizations should implement immediate mitigations including updating to Spring Web Flow version 2.4.5 or later, where this vulnerability has been patched, and configuring the MvcViewFactoryCreator with useSpringBinding set to true to enable proper data binding validation. Security teams should also review all view state definitions to ensure explicit data binding declarations are implemented for any form processing that accepts user input. Additional protective measures include implementing input validation at multiple layers, configuring web application firewalls to detect and block suspicious expression language patterns, and conducting comprehensive code reviews to identify vulnerable view state configurations. The ATT&CK framework categorizes this vulnerability under T1059.007 for Unix Shell and T1059.008 for PowerShell execution, as the exploitation typically results in command execution capabilities that can be leveraged for lateral movement and persistence within the compromised environment. Regular security assessments and vulnerability scanning should be implemented to identify applications running vulnerable versions of Spring Web Flow and ensure proper configuration hardening across all production environments.