CVE-2020-9484

When using Apache Tomcat versions 10.0.0-M1 to 10.0.0-M4, 9.0.0.M1 to 9.0.34, 8.5.0 to 8.5.54 and 7.0.0 to 7.0.103 if a) an attacker is able to control the contents and name of a file on the server; and b) the server is configured to use the PersistenceManager with a FileStore; and c) the PersistenceManager is configured with sessionAttributeValueClassNameFilter="null" (the default unless a SecurityManager is used) or a sufficiently lax filter to allow the attacker provided object to be deserialized; and d) the attacker knows the relative file path from the storage location used by FileStore to the file the attacker has control over; then, using a specifically crafted request, the attacker will be able to trigger remote code execution via deserialization of the file under their control. Note that all of conditions a) to d) must be true for the attack to succeed.

Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.

CVE-2020-9484 has a CVSS score of 7.0 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (10.0.0-M5, 9.0.35, 8.5.55, 7.0.104); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2020-9484? CVE-2020-9484 is a high-severity insecure deserialization vulnerability in org.apache.tomcat:tomcat-catalina (maven), affecting versions >= 10.0.0-M1, <= 10.0.0-M4. It is fixed in 10.0.0-M5, 9.0.35, 8.5.55, 7.0.104. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
2. How severe is CVE-2020-9484? CVE-2020-9484 has a CVSS score of 7.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2020-9484?
   • org.apache.tomcat:tomcat-catalina (maven) (versions >= 10.0.0-M1, <= 10.0.0-M4)
   • org.apache.tomcat.embed:tomcat-embed-core (maven) (versions >= 10.0.0-M1, <= 10.0.0-M4)
4. Is there a fix for CVE-2020-9484? Yes. CVE-2020-9484 is fixed in 10.0.0-M5, 9.0.35, 8.5.55, 7.0.104. Upgrade to this version or later.
5. Is CVE-2020-9484 exploitable, and should I be worried? Whether CVE-2020-9484 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-9484 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-9484?
   • Upgrade org.apache.tomcat:tomcat-catalina to 10.0.0-M5 or later
   • Upgrade org.apache.tomcat:tomcat-catalina to 9.0.35 or later
   • Upgrade org.apache.tomcat:tomcat-catalina to 8.5.55 or later
   • Upgrade org.apache.tomcat:tomcat-catalina to 7.0.104 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 10.0.0-M5 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 9.0.35 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 8.5.55 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 7.0.104 or later