GHSA-344f-f5vg-2jfj BIT-tomcat-2020-9484 CVE-2020-9484

Potential remote code execution in Apache Tomcat

High Maven

Severity: 7.0 / 10; High · CVSS 3.1
Exploit chance (EPSS): 55.52%; Chance of exploitation in the next 30 days. Higher than 99.04% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-502 Deserialization of Untrusted Data
Fix: Available; 2 packages have a fixed version

Description

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.

Affected versions

Maven

Package	Vulnerable	Fixed in
org.apache.tomcat.embed:tomcat-embed-core	`>= 10.0.0-M1, < 10.0.0-M5`	`10.0.0-M5`
org.apache.tomcat.embed:tomcat-embed-core	`>= 9.0.0, < 9.0.35`	`9.0.35`
org.apache.tomcat.embed:tomcat-embed-core	`>= 8.0.0, < 8.5.55`	`8.5.55`
org.apache.tomcat.embed:tomcat-embed-core	`>= 7.0.0, < 7.0.104`	`7.0.104`
org.apache.tomcat:tomcat-catalina	`>= 10.0.0-M1, < 10.0.0-M5`	`10.0.0-M5`
org.apache.tomcat:tomcat-catalina	`>= 9.0.0, < 9.0.35`	`9.0.35`
org.apache.tomcat:tomcat-catalina	`>= 8.0.0, < 8.5.55`	`8.5.55`
org.apache.tomcat:tomcat-catalina	`>= 7.0.0, < 7.0.104`	`7.0.104`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

org.apache.tomcat.embed:tomcat-embed-core Maven → `10.0.0-M5`

maven

<dependency><groupId>org.apache.tomcat.embed</groupId><artifactId>tomcat-embed-core</artifactId><version>10.0.0-M5</version></dependency>

gradle

implementation("org.apache.tomcat.embed:tomcat-embed-core:10.0.0-M5")

org.apache.tomcat:tomcat-catalina Maven → `10.0.0-M5`

maven

<dependency><groupId>org.apache.tomcat</groupId><artifactId>tomcat-catalina</artifactId><version>10.0.0-M5</version></dependency>

gradle

implementation("org.apache.tomcat:tomcat-catalina:10.0.0-M5")

Severity breakdown

CVSS 3.1 7.0

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack vector: Local
Attack complexity: High
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

Weakness

CWE-502: Deserialization of Untrusted Data

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

How to prevent it

Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
Implementation: When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
Implementation: Explicitly define a final object() to prevent deserialization.
Architecture and Design, Implementation: Make fields transient to protect them from deserialization. An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.
Implementation: Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.
Architecture and Design, Implementation: Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.
Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2020-9484

Packages

github.com/apache/tomcat

Timeline

May 21, 2020 Published
Aug 26, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-83qj-6fr2-vhqg Apache Tomcat: Potential RCE and/or information disclosure and/or information corruption with partial PUT	Critical Known exploited	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-qppj-fm5r-hxr3 HTTP/2 Stream Cancellation Attack	Medium Known exploited	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-xjgh-84hx-56c5 Unrestricted Upload of File with Dangerous Type Apache Tomcat	High Known exploited	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-cw54-59pw-4g8c Apache Tomcat Improper Access Control vulnerability	Critical Known exploited	Also affects org.apache.tomcat:tomcat-catalina
CVE-2020-1938 Improper Privilege Management in Tomcat	Critical Known exploited	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-pjfr-qf3p-3q25 When running Apache Tomcat on Windows with HTTP PUTs enabled it was possible to upload a JSP file to the server	High Known exploited	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-h3x4-894j-xpx5 Apache Tomcat's FORM authentication process has an Incorrect Authorization vulnerability	Critical	Also affects org.apache.tomcat.embed:tomcat-embed-core
GHSA-9xv2-5v5q-p794 Apache Tomcat's DIGEST authenticator has an Authentication Bypass by Capture-replay vulnerability	Critical	Also affects org.apache.tomcat.embed:tomcat-embed-core

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