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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-48802: 0.57% estimated exploitation activity in the next 30 days; percentile 47.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. Note: 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. Patches 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. - 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.

Published by the source

26 Jun 2026, 20:51 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cgwc-pv48-fhj5

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-cgwc-pv48-fhj5

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# Patch Next advisory brief: CVE-2026-48802

Advisory: python-engineio has unbound thread allocation that can cause denial of service
IDs: CVE-2026-48802, GHSA-cgwc-pv48-fhj5
Record: https://patchnext.com/advisories/cve-2026-48802 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: python-engineio 4.13.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI python-engineio: affected <= 4.13.1; fixed in 4.13.2

## Suggested inspection (read-only)
- `python -m pip show python-engineio`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on python-engineio.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-cgwc-pv48-fhj5 (OSV record GHSA-cgwc-pv48-fhj5 lists affected ranges: PyPI python-engineio >=0 <4.13.2 (fixed))
- Verified: https://github.com/advisories/GHSA-cgwc-pv48-fhj5 (GitHub-reviewed advisory GHSA-cgwc-pv48-fhj5 lists affected ranges: PyPI python-engineio >=0 <=4.13.1)

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