Critical Tomcat Vulnerability CVE-2025-31651: How To Fix

Hey guys! Let's talk about a critical security vulnerability, CVE-2025-31651, detected in tomcat-embed-core-8.5.11.jar. This is pretty serious, so buckle up and let's get into the details!

What is CVE-2025-31651?

This CVE-2025-31651 is a critical security flaw found in Apache Tomcat, specifically affecting versions from 11.0.0-M1 through 11.0.5, 10.1.0-M1 through 10.1.39, and 9.0.0.M1 through 9.0.102. It's related to the improper neutralization of escape, meta, or control sequences. In simpler terms, a sneaky request could bypass certain rewrite rules under specific, albeit unlikely, configurations. Now, why is this a big deal? Well, if these rewrite rules are in place to enforce security constraints, bypassing them means those constraints are effectively nullified. Imagine it like this: you have a locked door (rewrite rule), but there's a hidden passage (the vulnerability) that allows someone to walk right around it!

This vulnerability can lead to significant security breaches. The improper neutralization means that attackers can potentially manipulate requests in a way that the system interprets them differently than intended. This could involve injecting malicious code, accessing restricted areas, or performing unauthorized actions. The severity of this issue is highlighted by its CVSS score, which we'll dive into shortly. It’s crucial for anyone using these versions of Tomcat to understand the implications and take immediate action to mitigate the risk.

The core of the problem lies in how Tomcat handles certain rewrite rules. Rewrite rules are essentially instructions that tell the web server how to modify incoming requests before they reach the application. They are commonly used for tasks such as URL redirection, security filtering, and request manipulation. However, in this case, a specific type of request, crafted to exploit the vulnerability, can slip through the cracks. This bypass can occur if the rewrite rules are not configured to handle these specially crafted requests properly. It’s like having a filter with a hole in it – some things will still get through.

To fully grasp the potential impact, consider scenarios where rewrite rules are used to enforce critical security policies. For example, they might be used to block access to certain administrative areas or to filter out potentially harmful input. If an attacker can bypass these rules, they can gain unauthorized access to sensitive resources or inject malicious code into the application. This could lead to data breaches, system compromise, and other severe security incidents. Therefore, understanding the nature of CVE-2025-31651 and its implications is paramount for maintaining the security and integrity of your web applications running on Apache Tomcat.

Vulnerable Library: tomcat-embed-core-8.5.11.jar

The culprit in this scenario is the tomcat-embed-core-8.5.11.jar library, which is a core component of the Tomcat implementation. This JAR file is responsible for handling many of the fundamental operations within Tomcat, including request processing and security management. It’s like the engine of a car – if there’s a problem here, the whole system is at risk. The library's primary function is to provide the necessary classes and resources for embedding Tomcat within other applications, which is a common practice for Spring Boot applications and other Java-based web frameworks. This makes it a critical component, and any vulnerability within it can have far-reaching consequences.

The location of the vulnerable library within your project's dependency hierarchy is crucial for understanding the scope of the issue. In this particular case, the report indicates that tomcat-embed-core-8.5.11.jar is a transitive dependency, meaning it's not directly included in the project but is rather pulled in as a dependency of another library. Specifically, it's a dependency of spring-boot-starter-tomcat-1.5.2.RELEASE.jar, which itself is a dependency of spring-boot-starter-web-1.5.2.RELEASE.jar. This type of dependency relationship is common in modern Java projects that leverage dependency management tools like Maven or Gradle. It’s like tracing the branches of a tree to find where the problem lies.

Understanding the dependency hierarchy is essential for effective vulnerability remediation. When a vulnerability is found in a transitive dependency, it’s not enough to simply update the vulnerable library. You need to identify the direct dependency that brings it in and update that dependency instead. In this case, upgrading spring-boot-starter-tomcat would likely be the solution, as it would pull in a newer, patched version of tomcat-embed-core. This highlights the importance of regular dependency audits and updates as part of your overall security strategy. It's like making sure all the links in a chain are strong to prevent a break.

The provided information also points to the specific location of the vulnerable JAR file on the system: /home/wss-scanner/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/8.5.11/tomcat-embed-core-8.5.11.jar. This is the standard location for Maven dependencies stored in the local repository. Knowing the exact path can be helpful for verifying the presence of the vulnerable library and for confirming that the fix has been applied correctly. It’s like having a map to find the exact spot where the treasure (or in this case, the vulnerability) is located.

Impact of CVE-2025-31651

The impact of CVE-2025-31651 is severe, guys, due to the potential for attackers to bypass security constraints enforced by rewrite rules. Imagine your web application has rules to block malicious requests or restrict access to sensitive areas. This vulnerability lets attackers craft requests that slip past these rules, opening the door for serious trouble.

This critical vulnerability allows for improper neutralization of escape, meta, or control sequences. Attackers can manipulate requests in unexpected ways, causing the application to misinterpret them. This can lead to a range of malicious activities, such as unauthorized access to sensitive data, injection of malicious code, or complete system compromise. The potential for widespread damage makes it a top priority to address.

CVSS 3 Score: 9.8 (Critical)

The CVSS (Common Vulnerability Scoring System) v3 score for CVE-2025-31651 is a whopping 9.8 out of 10, which classifies it as critical. This score is a standardized way to assess the severity of a vulnerability, and a score this high indicates a significant risk. Let's break down what contributes to this score:

• Attack Vector: Network: This means the vulnerability can be exploited remotely over a network, making it accessible to a wide range of attackers. It's like leaving your front door unlocked, but the door is the internet, so anyone, anywhere, can try to walk in.
• Attack Complexity: Low: Exploiting this vulnerability doesn't require a high level of technical skill. The attack is relatively straightforward to execute, increasing the likelihood of it being exploited. Think of it as a lock that's easily picked.
• Privileges Required: None: An attacker doesn't need any prior access or credentials to exploit this vulnerability. They can launch the attack without any authentication, making it even more dangerous. It’s like someone being able to walk right into your house without needing a key or even knocking.
• User Interaction: None: The attack doesn't require any interaction from a user. This means an attacker can exploit the vulnerability without tricking someone into clicking a link or opening a file. It’s a completely hands-off attack, making it harder to prevent.
• Scope: Unchanged: While the vulnerability is serious, it's likely confined to the Tomcat instance itself and might not directly impact other systems. However, compromising the Tomcat instance can still have significant consequences for the application it serves.
• Confidentiality Impact: High: A successful exploit can lead to a significant loss of sensitive information. Attackers can gain access to confidential data, such as user credentials, financial information, or proprietary business data. It’s like someone getting the keys to your safe.
• Integrity Impact: High: The vulnerability can allow attackers to modify or corrupt data within the application. This can lead to data tampering, application malfunction, or even the injection of malicious content. It’s like someone changing the information in your important documents.
• Availability Impact: High: An attacker can disrupt the availability of the application, potentially causing a denial-of-service (DoS) situation. This means the application becomes unavailable to legitimate users, leading to business disruption and financial losses. It’s like someone turning off the lights in your house.

Given these factors, the critical CVSS score of 9.8 is justified. It underscores the urgent need to address this vulnerability and implement the recommended fixes.

Suggested Fix: Upgrade Tomcat

The recommended fix for CVE-2025-31651 is to upgrade your Tomcat version to a patched release. Specifically, the suggested fix is to upgrade to version 10.1.40 or later. This version includes the necessary security patches to address the vulnerability and prevent attackers from exploiting it. Upgrading is like reinforcing your door with a stronger lock and adding an alarm system.

Why is upgrading the preferred solution? Because it directly addresses the root cause of the vulnerability. The patched versions of Tomcat contain code changes that neutralize the attack vectors and prevent the bypass of rewrite rules. Simply put, upgrading ensures that your Tomcat instance is no longer susceptible to this particular flaw.

The fix resolution, as indicated in the details, is org.apache.tomcat.embed:tomcat-embed-core:10.1.40. This tells you the specific artifact and version to target when upgrading your dependencies. If you're using Maven or Gradle, you'll need to update your project's pom.xml or build.gradle file to specify the new version. This ensures that your project pulls in the patched version of the library. It's like swapping out the old, flawed part in your car with a new, improved one.

The fix was released on 2025-04-28, so it's readily available for implementation. The origin of the fix information points to the Openwall oss-security mailing list, a trusted source for security-related announcements and discussions. This adds credibility to the fix and provides assurance that it's a legitimate solution to the vulnerability. It’s like getting confirmation from a reliable expert that the repair is the right one.

To upgrade, you'll typically follow these steps:

1. Identify the Tomcat dependency: As we discussed earlier, you need to identify the direct dependency that brings in tomcat-embed-core. In this case, it's likely spring-boot-starter-tomcat.
2. Update your dependency management file: In your pom.xml (for Maven) or build.gradle (for Gradle) file, update the version of spring-boot-starter-tomcat to a version that includes the patched Tomcat version. For example, if you're using Spring Boot, you might need to upgrade to a newer Spring Boot version that depends on Tomcat 10.1.40 or later.
3. Rebuild your application: After updating the dependency, rebuild your application to include the new library version. This ensures that the patched code is deployed and running.
4. Test thoroughly: After upgrading, thoroughly test your application to ensure that everything is working as expected. This is crucial to verify that the upgrade didn't introduce any regressions or compatibility issues. It’s like taking your car for a test drive after the repair to make sure it’s running smoothly.

By following these steps, you can effectively mitigate the risk posed by CVE-2025-31651 and protect your application from potential attacks.

Conclusion

So, guys, CVE-2025-31651 is a critical vulnerability that needs your immediate attention if you're using the affected versions of Tomcat. The high CVSS score of 9.8 speaks volumes about the potential impact. Make sure to upgrade to version 10.1.40 or later to stay safe. Stay secure out there!