CVE-2026-48802

python-engineio has unbound thread allocation that can cause denial of service

Published Aug 11, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-cgwc-pv48-fhj5 python-engineio has unbound thread allocation that can cause denial of service
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Miguelgrinberg
Miguelgrinberg python-engineio
Vendors & Products Miguelgrinberg
Miguelgrinberg python-engineio
Type Values Removed Values Added
Description 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.
Title python-engineio has unbound thread allocation that can cause denial of service
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Aug 13, 2026, 2:35 PM
Reserved
May 22, 2026, 8:57 PM
Status
Deferred
Published
Aug 11, 2026, 7:17 PM
Modified
Sep 18, 2026, 8:09 PM