Spring4Shell (CVE-2022-22965) Vulnerability: Analysis, Impact, Mitigation

CVE-2022-22965, widely known as "Spring4Shell," is a critical remote code execution (RCE) vulnerability found in the popular Java Spring Framework. Think of it as an unlocked back door in certain web applications. This flaw allows an unauthenticated attacker to remotely execute malicious code on a target server, potentially giving them full control. Because the Spring Framework is so common in enterprise Java applications, this vulnerability sent shockwaves through the cybersecurity community, drawing comparisons to the infamous Log4Shell.

When was it Discovered?

The Spring4Shell vulnerability first came to light in late March 2022. It was initially disclosed to VMware by a security researcher and, shortly after, a proof-of-concept exploit was leaked online before an official patch was even available. This premature leak created a chaotic race between attackers trying to exploit it and defenders scrambling to figure out a fix. The official CVE identifier, CVE-2022-22965, was assigned on March 31, 2022, along with the release of patched Spring Framework versions.

Affected Products & Versions

The conditions for the Spring4Shell vulnerability are quite specific. It doesn't affect all applications using the Spring Framework. Here’s a breakdown of the specific stack that is vulnerable.

Product	Versions Affected	Fixed Versions / Patch Links
Spring Framework	5.3.0 to 5.3.17	5.3.18+
Spring Framework	5.2.0 to 5.2.19	5.2.20+
Prerequisite	Running on JDK 9 or higher	N/A
Prerequisite	Deployed as a traditional WAR file	N/A
Prerequisite	Uses spring-webmvc or spring-webflux	N/A

Note: Executable Spring Boot jars are generally not vulnerable by default, but the potential for exploitation can exist depending on specific configurations.

Spring4Shell Technical Description

So, how does this all go down? The root cause of the CVE-2022-22965 vulnerability lies in how the Spring Framework handles data binding with Plain Old Java Objects (POJOs). In certain configurations, a feature meant for convenience allows an attacker to send a specially crafted HTTP request. This request can manipulate the ClassLoader and access its properties.

By chaining together properties, an attacker can navigate through the object graph to write a malicious file, like a web shell, to an accessible location on the server's filesystem. For example, an attacker could craft a request that sets the logging properties of the Tomcat server to write a JSP file into the web application's root directory. Once that file is on the server, the attacker can just navigate to its URL to execute any code they want. The CVE-2022-22965 exploitability relies on this very specific, but powerful, request manipulation.

Tactics, Techniques & Procedures (TTPs)

Attackers leveraging the Spring4Shell vulnerability typically follow a clear pattern. Their primary goal is to achieve remote code execution. This usually starts with scanning the web for servers running vulnerable versions of the Spring Framework. Once a potential target is found, the attacker sends a crafted HTTP POST request to a vulnerable endpoint. This request is designed to modify server configurations, such as logging properties, to write a malicious web shell (e.g., a .jsp file) onto the server's disk. With the web shell in place, the attacker gains a persistent foothold to execute arbitrary commands, steal data, or pivot deeper into the network.

Indicators of Compromise

Looking for signs of a Spring4Shell attack? Your server logs are the best place to start. Key CVE-2022-22965 vulnerability indicators of compromise (IOCs) include suspicious HTTP requests containing strings like "class.module.classLoader". Also, keep an eye out for the creation of unexpected .jsp files in your web server's directories, especially in directories that are publicly accessible. Any outbound network connections from your web server to unusual IP addresses or domains could be another red flag, indicating a successful exploit and command-and-control (C2) communication.

Known Proof-of-Concepts & Exploits

Within hours of the vulnerability's disclosure, multiple CVE-2022-22965 proof-of-concept (PoC) exploits were published on platforms like GitHub. These PoCs demonstrated just how easy it was to drop a web shell on a vulnerable server. Cybercriminal groups and state-sponsored actors quickly weaponized these PoCs, incorporating them into their automated scanning and exploitation toolkits. Security researchers observed widespread scanning for the vulnerability, with attackers attempting to deploy everything from cryptominers to ransomware loaders. The availability of these public exploits meant that even low-skilled attackers could leverage the CVE-2022-22965 exploit.

How to Detect CVE-2022-22965 Vulnerability

CVE-2022-22965 vulnerability detection requires a multi-layered approach.

Host-Based Detection: Use an Endpoint Detection and Response (EDR) solution to monitor for suspicious file writes in web application directories. Look for processes spawned by your web server process (e.g., w3wp.exe or tomcat.exe) that are running unusual commands like cmd.exe or powershell.exe.
Log Analysis: Your best bet is to analyze your web server's access logs. Search for requests that contain suspicious parameter names like class.*, Class.*, *.class.*, or *.Class.*. A SIEM query could look for POST requests to any URL that includes these patterns in the request body or query parameters.
Network Signatures: Network Intrusion Detection Systems (NIDS) can use signatures to flag HTTP requests that match the known exploit patterns for CVE-2022-22965.

Impact & Risk of CVE-2022-22965 Vulnerability

The impact of a successful Spring4Shell exploit is severe. Because it leads to remote code execution, an attacker can effectively take over your server. This means they can:

Steal Sensitive Data: Access databases, files, and other confidential information stored on the server.
Deploy Ransomware: Encrypt your files and demand a ransom for their release.
Disrupt Services: Take down your web application, causing business interruption and financial loss.
Gain a Foothold: Use the compromised server as a launchpad to attack other systems within your network.

The risk is amplified by how widespread the Spring Framework is. Any public-facing web application running on a vulnerable stack is a prime target. Don't sleep on this one; the potential for damage is huge.

Mitigation & Remediation Strategies

If you're running a vulnerable version, it's time to act. Don't wait.

Patch Immediately: The most effective CVE-2022-22965 vulnerability mitigation is to update your Spring Framework to a patched version (5.3.18+ or 5.2.20+). This is the number one priority. Applying the CVE-2022-22965 patch closes the vulnerability.
Implement a Web Application Firewall (WAF): A properly configured WAF can block the malicious HTTP requests used to trigger the exploit, providing a critical layer of defense while you work on patching.
Apply Workarounds: If you can't patch right away, Spring's official guidance suggested creating a ControllerAdvice component to blacklist specific field patterns like class.* and module.*. This is a temporary fix and should not replace patching.
Monitor and Hunt: Continuously monitor your logs for any CVE-2022-22965 vulnerability IOCs. If you find evidence of compromise, isolate the affected server immediately and begin your incident response process. A robust security solution like Huntress's ITDR platform can help you hunt for and respond to these threats effectively.

Spring4Shell (CVE-2022-22965) Vulnerability FAQs

Spring4Shell (CVE-2022-22965) is a critical remote code execution vulnerability in the Java Spring Framework. It allows attackers to send a malicious web request to manipulate a server's ClassLoader. This lets them write a file, like a web shell, to the server, giving them full control.

Infection isn't like a traditional virus. Instead, an attacker actively exploits the vulnerability by sending a specially crafted HTTP request to a vulnerable web application. If successful, this exploit allows the attacker to execute their own code on the server.

Yes, absolutely. While patches have been available for years, unpatched and forgotten systems are still out there. Attackers continuously scan for these vulnerable servers, making Spring4Shell a persistent threat for any organization that hasn't diligently applied updates across all their applications.

The best protection is to patch your Spring Framework to a non-vulnerable version immediately. Beyond patching, you should use a Web Application Firewall (WAF) to block malicious requests and employ an EDR solution to monitor for any signs of post-exploitation activity, like suspicious file creation or processes.