Summary
RabbitMQ Java client has frame-level OOM: Math.min(maxInboundMessageBodySize, 0) defeats frame size enforcement
Vulnerability
In AMQConnection.java (line 435-436), after Connection.Tune negotiation, the frame-max limit is set via:
_frameHandler.setFrameMax(
Math.min(this.maxInboundMessageBodySize, frameMax));
When frameMax = 0 (meaning "unlimited" per AMQP spec), Math.min(67108864, 0) = 0. This value is then passed to Utils.framePayloadLimit(0) which returns Integer.MAX_VALUE (line 77-79 of Utils.java):
static int framePayloadLimit(int frameMax) {
if (frameMax <= 0) {
return Integer.MAX_VALUE;
}
// ...
}
This completely defeats the maxInboundMessageBodySize protection (default 64MB) at the frame level.
Attack Scenario
A malicious AMQP server (or MITM) sends Connection.Tune with frameMax=0:
- Client defaults:
requestedFrameMax = 0(ConnectionFactory.DEFAULT_FRAME_MAX, line 82) negotiatedMaxValue(0, 0)=Math.max(0, 0)= 0 (line 673-676)Math.min(maxInboundMessageBodySize, 0)= 0, 64MB cap defeatedframePayloadLimit(0)=Integer.MAX_VALUE, no frame size enforcement- Attacker sends a single frame with
frameSize = 0x1FFFFFFF(~500MB) Frame.readFrom()(line 135) executesnew byte[frameSize], OOM crash
The frame does not need to be a body frame, method frames, header frames, or heartbeat frames with a crafted size field all trigger the allocation before any content-level check fires.
Root Cause
The AMQP spec uses frameMax=0 to mean "unlimited", but Math.min treats it as the integer value zero. The intent of line 435-436 was to take the smaller of the two limits, but when one limit uses 0-means-unlimited semantics, Math.min always selects the zero, disabling the other limit.
Affected Code
AMQConnection.java:435-436,Math.minwith 0-means-unlimitedUtils.java:77-79,framePayloadLimit(0)returnsInteger.MAX_VALUEFrame.java:135,new byte[frameSize]allocation siteConnectionFactory.java:82,DEFAULT_FRAME_MAX = 0
Impact
- Default configuration is vulnerable: Both
requestedFrameMax(client) and legitimate servers'frameMaxin Tune may be 0 - Single-frame OOM: One malicious frame triggers up to ~2GB allocation (
Integer.MAX_VALUEbytes) - Bypasses existing protection:
maxInboundMessageBodySize(introduced to cap allocations at 64MB) is entirely defeated at the frame level - Different from ValueReader OOM: This is a frame-layer allocation in
Frame.readFrom(), not a value-layer allocation inValueReader.readBytes()
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
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.
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int effectiveFrameMax = (frameMax == 0)
? this.maxInboundMessageBodySize
: Math.min(this.maxInboundMessageBodySize, frameMax);
_frameHandler.setFrameMax(effectiveFrameMax);
This treats frameMax=0 as "use maxInboundMessageBodySize as the cap" instead of "zero".
Frequently Asked Questions
- What is CVE-2026-75516? CVE-2026-75516 is a high-severity allocation of resources without limits or throttling vulnerability in com.rabbitmq:amqp-client (maven), affecting versions < 5.34.0. It is fixed in 5.34.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
- Which versions of com.rabbitmq:amqp-client are affected by CVE-2026-75516? com.rabbitmq:amqp-client (maven) versions < 5.34.0 is affected.
- Is there a fix for CVE-2026-75516? Yes. CVE-2026-75516 is fixed in 5.34.0. Upgrade to this version or later.
- Is CVE-2026-75516 exploitable, and should I be worried? Whether CVE-2026-75516 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-2026-75516 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-2026-75516? Upgrade
com.rabbitmq:amqp-clientto 5.34.0 or later.