CVE-2020-9484
Description
A deserialization flaw was discovered in Apache Tomcat's use of a FileStore. Under specific circumstances, an attacker can use a specially crafted request to trigger Remote Code Execution through deserialization of the file under their control. The highest threat from the vulnerability is to data confidentiality and integrity as well as system availability.
Statement
In Red Hat Enterprise Linux 8, Red Hat Certificate System 10 and Identity Management are using the pki-servlet-engine component, which embeds a vulnerable version of Tomcat. However, in these specific contexts, the prerequisites to the vulnerability are not met. The PersistentManager is not set, and a SecurityManager is used. The use of pki-servlet-engine outside of these contexts is not supported. As a result, the vulnerability can not be triggered in supported configurations of these products. A future update may update Tomcat in pki-servlet-engine.
Red Hat Satellite do not ship Tomcat and rather use its configuration. The product is not affected because configuration does not make use of PersistanceManager or FileStore. Tomcat updates can be obtain from Red Hat Enterprise Linux (RHEL) RHSA.
Mitigation
Users may configure the PersistenceManager with an appropriate value for sessionAttributeValueClassNameFilter to ensure that only application provided attributes are serialized and deserialized. For more details about the configuration, refer to the Apache Tomcat 9 Configuration Reference https://tomcat.apache.org/tomcat-9.0-doc/config/manager.html.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | 7 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
AV should be Local because the attacker requires a malicious file on a Tomcat server's local filesystem to exploit successfully.
There are sufficient factors beyond the attacker's control: a FileStore must be configured, PersistanceManager must have default value configured for sessionattributeclassnamefilter, local access and paths known. This set of conditions, we feel, reflects AC:H rather than AC:L.
PR should be Low because the attacker requires write privileges to a Tomcat server's filesystem but does not require significantly higher (e.g., administrative) permissions.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Application Data; Unexpected State
Attackers can modify unexpected objects or data that was assumed to be safe from modification. Deserialized data or code could be modified without using the provided accessor functions, or unexpected functions could be invoked.
Availability
Technical Impact: DoS: Resource Consumption (CPU)
If a function is making an assumption on when to terminate, based on a sentry in a string, it could easily never terminate.
Other
Technical Impact: Varies by Context
The consequences can vary widely, because it depends on which objects or methods are being deserialized, and how they are used. Making an assumption that the code in the deserialized object is valid is dangerous and can enable exploitation. One example is attackers using gadget chains to perform unauthorized actions, such as generating a shell.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
