CVE-2026-48802
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk24th percentile - higher than 24% of all known CVEs
Summary
python-engineio before version 4.13.2 allows an attacker to cause the creation of unnecessary background threads in the server by exploiting the heartbeat mechanism, which launches a thread when a new connection is received and when the client sends a PONG packet. This issue primarily affects synchronous servers. Version 4.13.2 fixes this by launching the initial thread only after client authentication and ensuring only one thread per client.
Risk Assessment
An attacker can cause resource exhaustion on the server, potentially leading to denial of service.
Recommendation
Update python-engineio to version 4.13.2 or later.
Original NVD description (English source)
python-engineio is a Python implementation of the Engine.IO realtime client and server. Prior to version 4.13.2, an attacker can cause the creation of unnecessary background threads in the python-engineio server by exploiting the heartbeat mechanism, which launches a thread when a new connection is received, and when the client sends a PONG packet. This issue primarily affects synchronous servers. Asynchronous servers allocate background tasks instead of physical threads, which are lightweight and less likely to cause denial of service. However, the fix that was implemented was also applied to the asynchronous case. Version 4.13.2 addresses this issue as follows: The initial background thread (or async task( for heartbeat management is only launched if a client passes authentication in the `connect` handler; and the server now ensures that there is only one background heatbeat thread (or async task) per client at a given point in time. Out of sequence PONG packets are now discarded when an active heartbeat thread is already running.