CVE-2026-48804 in python-socketio
Summary
by MITRE • 08/11/2026
python-socketio is a Python implementation of the Socket.IO realtime client and server. The python-socketio server stores binary `EVENT` and `ACK` messages in memory while it waits to receive their binary attachments. Once all the attachments are received, these messages are then processed. Prior to version 5.16.4, an attacker can submit a binary message and intentionally omit sending one or more of its attachments to cause the message along with the partial list of received attachments to stay in memory for a long time. Version 5.16.4 takes the following measures to address this issue: Binary packets are only accepted from authenticated clients and, when a client disconnects, the server checks if there is a partial binary message being held for the client and deletes it.
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Analysis
by VulDB Data Team • 08/11/2026
The python-socketio library implements the Socket.IO protocol for real-time communication in Python applications, providing both client and server capabilities for bidirectional event-based communication between web clients and servers. This vulnerability affects the server implementation where binary messages are processed through a multi-step mechanism involving initial message receipt followed by attachment collection before final processing occurs.
The technical flaw resides in the server's handling of binary packet transmission where EVENT and ACK messages containing binary attachments are stored in memory during the attachment collection phase. The vulnerability stems from insufficient validation and cleanup mechanisms that allow attackers to submit partial binary messages without completing the required attachment sequence, causing these incomplete message fragments to remain in memory indefinitely.
This design creates a memory exhaustion vulnerability classified under CWE-400 as it allows for uncontrolled resource consumption through persistent storage of incomplete binary message data. The issue represents a denial of service vector where an attacker can continuously submit partial binary messages to fill available server memory, eventually causing legitimate clients to be unable to connect or process valid requests.
The operational impact extends beyond simple resource exhaustion to potentially affect system availability and performance stability. Servers running vulnerable versions of python-socketio could experience gradual memory degradation until complete system failure occurs, particularly affecting applications with high connection volumes or limited memory resources. This vulnerability directly maps to ATT&CK technique T1499.004 for resource exhaustion attacks.
Version 5.16.4 introduced critical mitigations addressing both authentication and cleanup mechanisms. The implementation now requires client authentication before accepting binary packets, reducing the attack surface by preventing unauthenticated users from submitting malicious partial messages. Additionally, enhanced session management includes automatic cleanup of partial binary message data upon client disconnection events, ensuring that incomplete message fragments are promptly removed from memory regardless of whether they were submitted by legitimate authenticated clients or malicious actors.
The security improvements align with defense-in-depth principles and demonstrate proper input validation and resource management practices. These changes ensure that binary packet processing maintains bounded memory usage while preserving legitimate application functionality for authenticated users. The mitigation strategy effectively addresses the root cause by implementing both access control restrictions and automatic resource cleanup procedures that prevent persistent memory accumulation from malicious or accidental partial message submissions.
This vulnerability highlights the importance of proper resource management in real-time communication frameworks and demonstrates how seemingly benign protocol features can create security weaknesses when not properly bounded or validated. The fix represents a comprehensive approach to preventing resource exhaustion attacks while maintaining backward compatibility for legitimate use cases within authenticated sessions.