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Date: Wed, 20 May 2020 16:22:21 +0100
From: Mark Thomas <markt@...che.org>
To: oss-security@...ts.openwall.com
Subject: CVE-2020-9484 Apache Tomcat Remote Code Execution via session
 persistence

CVE-2020-9484 Apache Tomcat Remote Code Execution via session persistence

Severity: High

Vendor: The Apache Software Foundation

Versions Affected:
Apache Tomcat 10.0.0-M1 to 10.0.0-M4
Apache Tomcat 9.0.0.M1 to 9.0.34
Apache Tomcat 8.5.0 to 8.5.54
Apache Tomcat 7.0.0 to 7.0.103

Description:
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.

Mitigation:
- Upgrade to Apache Tomcat 10.0.0-M5 or later
- Upgrade to Apache Tomcat 9.0.35 or later
- Upgrade to Apache Tomcat 8.5.55 or later
- Upgrade to Apache Tomcat 7.0.104 or later
Alternatively, users may configure the PersistenceManager with an
appropriate value for sessionAttributeValueClassNameFilter to ensure
that only application provided attributes are serialized and deserialized.

Credit:
This issue was discovered and reported responsibly to the Apache Tomcat
Security Team by report by jarvis threedr3am of pdd security research

References:
[1] http://tomcat.apache.org/security-10.html
[2] http://tomcat.apache.org/security-9.html
[3] http://tomcat.apache.org/security-8.html
[4] http://tomcat.apache.org/security-7.html

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