CVE-2026-31814 in rust-yamux
Summary
by MITRE • 03/13/2026
Yamux is a stream multiplexer over reliable, ordered connections such as TCP/IP. From 0.13.0 to before 0.13.9, a specially crafted WindowUpdate can cause arithmetic overflow in send-window accounting, which triggers a panic in the connection state machine. This is remotely reachable over a normal network connection and does not require authentication. This vulnerability is fixed in 0.13.9.
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Analysis
by VulDB Data Team • 03/20/2026
The vulnerability described in CVE-2026-31814 affects Yamux, a stream multiplexer implementation that operates over reliable, ordered connections such as TCP/IP. This protocol enables multiple streams to be multiplexed over a single connection, which is commonly used in distributed systems and network communication frameworks. The affected versions range from 0.13.0 through 0.13.8, where a specific flaw in the window update mechanism creates a critical security issue. The vulnerability stems from improper handling of window size calculations during stream multiplexing operations, specifically within the send-window accounting system that manages flow control between communicating parties. This flaw represents a significant concern because it can be exploited remotely without requiring any authentication credentials, making it particularly dangerous in networked environments where unauthenticated connections are possible.
The technical implementation of this vulnerability involves an arithmetic overflow condition that occurs when processing specially crafted WindowUpdate messages. The send-window accounting mechanism in Yamux maintains state about available buffer space for data transmission, and when a maliciously constructed WindowUpdate message is received, it causes integer overflow during the calculation of available window space. This overflow leads to a panic condition within the connection state machine, effectively crashing the application or service that is using the vulnerable Yamux implementation. The panic state machine failure results in a denial of service condition where the connection becomes unusable and requires manual intervention or restart to restore functionality. This type of vulnerability falls under the CWE-191 category of Integer Underflow (Wrap or Wraparound) and is particularly dangerous because it can be triggered through normal network traffic without any special privileges or authentication requirements.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially be exploited in broader attack scenarios within networked applications that rely on Yamux for connection management. Systems using vulnerable versions of Yamux may experience unexpected service interruptions, particularly in environments where high availability is critical. The remote exploitability means that attackers can target systems from external networks without needing to establish any form of authenticated access first, making this vulnerability particularly attractive for automated attacks. Network monitoring systems may detect unusual connection behavior or service disruptions, but the root cause of the panic condition may not be immediately apparent to security analysts. This vulnerability can affect any application or service that implements Yamux for stream multiplexing, including but not limited to distributed systems, microservices architectures, and network communication frameworks that depend on reliable ordered connections. The lack of authentication requirements makes this a particularly concerning issue for services exposed to the internet or untrusted network environments.
Mitigation strategies for this vulnerability primarily involve upgrading to Yamux version 0.13.9 or later, which contains the necessary fixes for the arithmetic overflow condition in window update handling. Organizations should prioritize patching affected systems as soon as possible, particularly those running services that are exposed to external networks or untrusted environments. Network administrators should monitor for unusual connection behavior or service disruptions that might indicate exploitation attempts. Additional defensive measures include implementing network segmentation to limit exposure of vulnerable systems, deploying intrusion detection systems that can identify malformed WindowUpdate messages, and establishing robust monitoring procedures for connection state anomalies. The fix implemented in version 0.13.9 addresses the core issue by properly validating window update values and preventing arithmetic overflow conditions during send-window accounting operations. Security teams should also consider implementing application-level firewalls or proxy systems that can filter out malformed or suspicious WindowUpdate messages before they reach vulnerable applications. This vulnerability demonstrates the importance of proper input validation and arithmetic overflow protection in network protocols, particularly those handling flow control mechanisms that are critical to connection stability and service availability.