OpenTelemetry Java Instrumentation allows auto‑instrumentation for Java applications. In versions before 2.26.1 the RMI instrumentation registers a custom endpoint that deserializes incoming data without applying serialization filters. This unsandboxed deserialization can be triggered by a remote attacker with access to a JMX or RMI port, leading to arbitrary code execution. The vulnerability is a classic unsafe deserialization flaw (CWE‑502) that permits an attacker to run arbitrary code with the privileges of the JVM process.

Systems running OpenTelemetry Java Instrumentation on Java 16 or earlier and configured with a network‑exposed JMX/RMI port are affected. The issue applies to any deployment that attaches the Java agent (`-javaagent`) of OpenTelemetry and does not disable RMI integration. The relevant product is the OpenTelemetry Java Instrumentation library; versions older than 2.26.1 are vulnerable. Users of JDK 17 or newer are not impacted and no remediation is required, but upgrading remains recommended.

The CVSS score of 9.3 classifies the flaw as critical. Because the exploit requires three conditions – the vulnerable agent, a reachable JMX/RMI port, and a gadget‑chain library on the classpath – the threat is high but not trivially exploitable by all attackers. Attackers need to be able to connect to the RMI port over the network, which is often behind firewalls; nevertheless, any exposed port could be abused. The EPSS score is not available, but the vulnerability is not listed in the CISA KEV catalog. Given the severity and the possibility of remote code execution, immediate action is strongly advised.