CVE-2026-66079 in RabbitMQ
Summary
by MITRE • 09/23/2026
RabbitMQ is a messaging and streaming broker. Prior to versions 3.13.15, 4.0.20, 4.1.11, and 4.2.6, parse_array_primitive/2 for constructor 0x45 (list0) returns an element with byte-width B = 0. The enclosing array32 parser at line 148 reads a 4-byte Count from the wire and loops Count times consuming B bytes each , with B = 0, no input is consumed and the loop builds a list of Count empty elements bounded only by the 32-bit field. The SASL-mechanisms / SASL-init frame is parsed by amqp10_framing:decode_bin/1 from rabbit_amqp_reader.erl:412 before authentication completes. The pre-auth incoming_max_frame_size (default 8192 bytes) caps the frame, not the Count field, so a 19-byte payload with Count = 0xFFFFFFFF is accepted. No max_heap_size is set on the reader process. An unauthenticated network attacker can crash any RabbitMQ node that has the AMQP 1.0 listener enabled (default port 5672) by sending a single ~19-byte frame. The reader process attempts to build a list of ~4 billion empty elements, exhausting heap memory and terminating the Erlang VM. All tenants and protocols on the node lose service. Preconditions include Network reachability to the AMQP listener (port 5672, enabled by default) No authentication required. This issue is fixed in versions 3.13.15, 4.0.20, 4.1.11, and 4.2.6.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified involves a critical resource exhaustion flaw within the RabbitMQ messaging broker, specifically affecting its AMQP 1.0 protocol implementation prior to versions 3.13.15, 4.0.20, 4.1.11, and 4.2.6. This issue stems from an improper handling of array parsing logic in the Erlang-based core components responsible for decoding binary frames. The root cause lies within the parse_array_primitive/2 function associated with constructor 0x45, which is designated for list types. When processing this specific data structure, the parser incorrectly returns an element characterized by a byte-width value of zero. This deviation from expected behavior creates a logical loop condition that fails to consume input data during iteration, thereby enabling a denial-of-service scenario through unbounded memory allocation.
The technical mechanism exploits the interaction between the array32 parser and the SASL authentication handshake process. Specifically, the amqp10_framing:decode_bin/1 function in rabbit_amqp_reader.erl processes incoming frames before authentication is fully completed. The system relies on a pre-authentication limit known as incoming_max_frame_size to cap the total size of received data, which defaults to 8192 bytes. However, this constraint applies only to the overall frame payload and not to the internal Count field within that payload. An attacker can craft a maliciously small packet containing approximately nineteen bytes where the four-byte count field is set to its maximum unsigned integer value, 0xFFFFFFFF or roughly four billion elements. Because each element in the resulting list has zero byte width, the parser enters an infinite loop attempting to construct this massive data structure without consuming any actual network input beyond the initial header.
The operational impact of this vulnerability is severe and immediate for any RabbitMQ node with the AMQP 1.0 listener enabled on port 5672, which is active by default in standard installations. Since no max_heap_size limit is enforced on the reader process handling these frames, the Erlang Virtual Machine attempts to allocate memory for billions of empty list elements. This action rapidly exhausts the available heap memory allocated to that specific process and eventually impacts the broader node resources. The result is a complete crash of the RabbitMQ instance due to out-of-memory conditions. Consequently, all tenants connected to this broker and any other protocols running on the same node experience an immediate loss of service, disrupting messaging operations across the entire infrastructure dependent on that single point of failure.
From a classification perspective, this vulnerability aligns with CWE-400 Uncontrolled Resource Consumption, as the application fails to properly limit the amount of resources consumed by processing untrusted input. It also relates to CWE-787 Out-of-bounds Write in terms of memory allocation logic, although the primary manifestation is resource exhaustion rather than arbitrary code execution. In the context of the MITRE ATT&CK framework, this exploit corresponds to T1499 Endpoint Denial of Service, specifically leveraging application layer protocols to disrupt service availability without requiring authentication credentials. The lack of pre-authentication validation for internal data structure limits allows an unauthenticated network attacker to trigger this condition remotely with minimal effort and a very small payload size.
Mitigation strategies primarily involve upgrading the RabbitMQ installation to one of the fixed versions mentioned, which include 3.13.15, 4.0.20, 4.1.11, or 4.2.6. These updates correct the parsing logic for array primitives and ensure that internal count fields are validated against reasonable bounds before memory allocation occurs. For environments where immediate patching is not feasible, administrators should consider disabling the AMQP 1.0 listener if it is not strictly required, thereby removing the attack surface associated with this specific code path. Additionally, implementing network-level access control lists to restrict connectivity to port 5672 can provide a layer of defense against unauthenticated exploitation attempts until the software update is applied.