Summary
RabbitMQ: JSONReader in the default JSON-RPC mapper never terminates on truncated input, causing DoS
com.rabbitmq.tools.json.JSONReader.read() never returns when its input ends inside a quoted string or a // line comment. Both scanners walk the input with StringCharacterIterator.next() but only compare against a delimiter, so once the iterator reaches CharacterIterator.DONE () they loop forever. The string scanner (string(), line 210, while (c != sep)) also appends to a StringBuilder every iteration, so it fills the heap and throws OutOfMemoryError, taking down the JVM. The comment scanner (skipWhiteSpace(), lines 89-92, while (c != '\n')) pins a thread at 100% CPU with no allocation.
This is reachable with a single message. JsonRpcServer and JsonRpcClient fall back to DefaultJsonRpcMapper whenever no mapper is passed (JsonRpcServer.java:84 and :114, JsonRpcClient.java:186), and that mapper hands the raw message body straight to JSONReader.read() (DefaultJsonRpcMapper.java:42 for the server request, :52 for the client reply). A caller that can publish to the RPC request queue hangs the server; a malicious or MITM'd JSON-RPC service does the same to a client.
Proof of concept
Against amqp-client 5.36.0 from Maven Central:
import com.rabbitmq.tools.jsonrpc.DefaultJsonRpcMapper;
public class Poc {
public static void main(String[] args) {
DefaultJsonRpcMapper mapper = new DefaultJsonRpcMapper();
mapper.parse("{\"method\":\"x", String.class); // unterminated string
// mapper.parse("//", String.class); // unterminated // comment
System.out.println("unreachable");
}
}
java -Xmx64m -cp amqp-client-5.36.0.jar:. Poc throws OutOfMemoryError: Java heap space in about 0.1s and never prints. Swapping in the // line spins at 100% CPU and never returns. A well-formed body such as {"method":"x"} returns immediately.
Scope and fix
Only applications using the JSON-RPC-over-AMQP tooling (com.rabbitmq.tools.jsonrpc) with the default DefaultJsonRpcMapper are affected. DefaultJsonRpcMapper and JSONReader are deprecated in favour of JacksonJsonRpcMapper, but both still ship and remain the default when no mapper is supplied. The fix is to stop both loops at CharacterIterator.DONE.
Impact
Availability. One small, unauthenticated message stops a JSON-RPC endpoint: the unterminated string exhausts the heap, the unterminated comment pins a thread forever. Neither is recoverable per request - JsonRpcServer.doCall only catches ClassCastException, and an OutOfMemoryError affects the whole process.
CVE-2026-106121 has a CVSS score of 4.9 (Medium). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.36.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-106121? CVE-2026-106121 is a medium-severity security vulnerability in com.rabbitmq:amqp-client (maven), affecting versions <= 5.36.0. It is fixed in 5.36.1.
- How severe is CVE-2026-106121? CVE-2026-106121 has a CVSS score of 4.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of com.rabbitmq:amqp-client are affected by CVE-2026-106121? com.rabbitmq:amqp-client (maven) versions <= 5.36.0 is affected.
- Is there a fix for CVE-2026-106121? Yes. CVE-2026-106121 is fixed in 5.36.1. Upgrade to this version or later.
- Is CVE-2026-106121 exploitable, and should I be worried? Whether CVE-2026-106121 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-106121 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-106121? Upgrade
com.rabbitmq:amqp-clientto 5.36.1 or later.