CVE-2026-73568 in py-libp2p
Summary
by MITRE • 08/13/2026
py-libp2p is the Python implementation of the libp2p networking stack. In 0.7.0 and earlier, the yamux handle_incoming() method in libp2p/stream_muxer/yamux/yamux.py reads an attacker-controlled 32-bit DATA frame length with read_exactly() before validating it against MAX_WINDOW_SIZE or checking whether stream_id exists. A peer that completes the standard Noise handshake can send a 12-byte frame declaring a 0xFFFFFFFF body and then withhold the body, causing the sequential yamux read loop used by the default new_host() configuration to block and preventing every stream on that connection from making progress. No fixed version is available as of this review.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability in py-libp2p version 0.7.0 and earlier represents a critical denial of service condition within the yamux stream multiplexer implementation. This flaw exists in the handle_incoming() method located at libp2p/stream_muxer/yamux/yamux.py where the system processes incoming DATA frames without proper validation of frame length parameters. The vulnerability stems from a fundamental design issue where attacker-controlled 32-bit data frame lengths are read using read_exactly() function before any validation occurs against established bounds including MAX_WINDOW_SIZE or stream_id existence checks. This primitive violation creates a path for malicious actors to manipulate the frame processing logic through carefully crafted network packets.
The technical exploitation of this vulnerability relies on the attacker completing the standard Noise handshake which grants them access to the yamux connection layer. Once authenticated, the attacker can send a specifically formatted 12-byte frame that declares a 0xFFFFFFFF body length, effectively creating an enormous data payload request. The malicious peer then withholds the actual body data, causing the yamux read loop to block indefinitely while waiting for data that will never arrive. This behavior demonstrates a classic resource exhaustion pattern where legitimate connection processing becomes paralyzed due to unvalidated input handling. The impact extends beyond individual streams as the blocking occurs at the connection level, preventing all streams on that specific connection from making forward progress.
This vulnerability directly maps to CWE-129 Insufficient Input Validation and CWE-400 Uncontrolled Resource Consumption within the Common Weakness Enumeration framework. The flaw also aligns with ATT&CK technique T1499.004 for Network Denial of Service by exploiting resource consumption patterns in network protocols. From a practical operational standpoint, this vulnerability poses significant risk to distributed applications using py-libp2p as it can be exploited by any peer that successfully completes the Noise handshake process. The blocking behavior affects connection stability and can potentially lead to cascading failures in larger network topologies where multiple peers depend on stable stream multiplexer operations.
The default new_host() configuration in py-libp2p makes this vulnerability particularly dangerous as it represents the standard deployment pattern for most applications using the library. No fixed version exists at the time of this review, leaving affected systems vulnerable to exploitation. The lack of immediate remediation options forces organizations to either implement custom workarounds or accept the risk of service disruption. Mitigation strategies should focus on input validation improvements within the yamux implementation, including proper bounds checking before data reading operations and implementing timeouts for frame processing. Additionally, network-level monitoring should be enhanced to detect anomalous frame length patterns that could indicate exploitation attempts.