CVE-2023-21839: 
Oracle WebLogic Server vulnerability analysis and mitigation

Oracle WebLogic Server contains a critical vulnerability (CVE-2023-21839) that affects versions 12.2.1.3.0, 12.2.1.4.0, and 14.1.1.0.0. This easily exploitable vulnerability allows unauthenticated attackers with network access via T3 or IIOP protocols to compromise the server. The vulnerability was disclosed in January 2023 and has a CVSS 3.1 Base Score of 7.5 (Oracle Advisory).

CVE-2023-21839 is not a typical deserialization vulnerability. The vulnerability occurs after deserialization when an attacker can create an object in the target's memory and later trigger another function that utilizes that deserialized object without proper sanity checks. The vulnerability specifically involves the ForeignOpaqueReference class, which implements the OpaqueReference interface. The bug occurs in the getReferent() method, which performs a remote JNDI loading operation using an attacker-controlled remoteJNDIName parameter (SentinelOne).

Successful exploitation of this vulnerability can result in unauthorized access to critical data or complete access to all Oracle WebLogic Server accessible data. The vulnerability primarily impacts confidentiality, with a High severity rating for confidentiality impact in the CVSS scoring (NVD).

Oracle has released patches for this vulnerability in the January 2023 Critical Patch Update. If immediate patching is not possible, temporary mitigation can be implemented by blocking external access to the T3/T3s protocol on port 7001 using a connection filter. This can be done by accessing the WebLogic console and disabling IIOP or by implementing connection filter rules to block external T3/T3s protocol access (SentinelOne).