CVE-2026-67553 Overview
CVE-2026-67553 is a denial of service vulnerability in Apache Qpid Proton-Dotnet, an AMQP 1.0 protocol library used by .NET applications for messaging integration. An authenticated attacker can exceed the session flow control incoming window, exhausting resources on the target and preventing legitimate message processing. The flaw is categorized under [CWE-770] (Allocation of Resources Without Limits or Throttling). Apache Qpid Proton-Dotnet versions through 1.0.0 are affected, and the project maintainers have released version 1.1.0 to fix the issue.
Critical Impact
An authenticated attacker can trigger denial of service against AMQP messaging services by violating the negotiated session flow control window.
Affected Products
- Apache Qpid Proton-Dotnet versions through 1.0.0
- .NET applications embedding the affected AMQP client library
- Messaging services relying on Qpid Proton-Dotnet session handling
Discovery Timeline
- 2026-08-05 - CVE-2026-67553 published to NVD
- 2026-08-05 - Last updated in NVD database
Technical Details for CVE-2026-67553
Vulnerability Analysis
Apache Qpid Proton-Dotnet implements the AMQP 1.0 protocol, which uses session-level flow control to bound the number of transfer frames a peer can send before receiving additional credit. The receiving side advertises an incoming window that limits how many unsettled transfers it will accept. The vulnerability arises because the library does not properly enforce that limit against a misbehaving authenticated peer.
An attacker who has already authenticated to the broker or peer can send more transfer frames than the negotiated incoming window permits. Because the library fails to reject or throttle these excess frames, internal buffers and session state grow beyond expected bounds. This leads to resource exhaustion and denial of service against the messaging endpoint.
The issue tracks with [CWE-770], which covers allocation of resources without limits or throttling. See the Apache Security Discussion and the Openwall OSS Security Mail for the vendor announcement.
Root Cause
The root cause is missing enforcement of the AMQP session incoming window limit on the receive path. The library trusts the peer to honor the advertised window rather than validating and dropping frames that violate it. As transfers accumulate beyond the expected boundary, memory and processing overhead expand until the process degrades or fails.
Attack Vector
Exploitation requires valid authentication to the AMQP endpoint. Once connected, the attacker opens a session and issues transfer frames at a rate exceeding the negotiated incoming window. Sustained frame flooding starves the service of resources, disrupting message delivery for other tenants and clients.
No verified public exploit code is available. The behavior can be described in prose: an authenticated peer submits AMQP transfer performatives beyond the credit granted by the receiver, and the receiver continues to accept and buffer them rather than terminating the offending session.
Detection Methods for CVE-2026-67553
Indicators of Compromise
- Abnormal growth in memory consumption or session buffer counts on AMQP brokers or clients using Qpid Proton-Dotnet
- Authenticated AMQP sessions transmitting transfer frame volumes inconsistent with advertised session credit
- Repeated session resets, timeouts, or crashes correlated with a single authenticated principal
Detection Strategies
- Inventory .NET applications and services using Apache Qpid Proton-Dotnet and identify versions at or below 1.0.0
- Instrument AMQP endpoints to log session-level flow control state and flag peers that exceed advertised windows
- Correlate authentication logs with resource utilization spikes on messaging hosts to identify abusive principals
Monitoring Recommendations
- Track process memory, thread count, and open session counts for services hosting Qpid Proton-Dotnet
- Alert on sustained transfer frame rates that outpace credit issuance from the receiver
- Forward AMQP broker and application logs to a centralized analytics platform to enable cross-session correlation
How to Mitigate CVE-2026-67553
Immediate Actions Required
- Upgrade Apache Qpid Proton-Dotnet to version 1.1.0 or later across all affected .NET applications
- Audit accounts authorized to open AMQP sessions and revoke credentials that are no longer required
- Restrict network exposure of AMQP endpoints to trusted client ranges where operationally feasible
Patch Information
The Apache Qpid project has released Qpid Proton-Dotnet version 1.1.0, which enforces the session flow control incoming window and rejects transfers that exceed the negotiated credit. Refer to the Apache Security Discussion for release details and upgrade guidance.
Workarounds
- Apply strict authentication and authorization policies to limit which principals can open AMQP sessions
- Enforce per-connection resource quotas at the broker or host level to contain the blast radius of misbehaving peers
- Deploy rate limiting or connection throttling in front of AMQP endpoints until affected libraries are upgraded
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
