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Fencer Vulns
high 7.5

CVE-2026-48802 json

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

published 2026-06-26 4 mo ago modified 2026-09-18 51 d ago also GHSA-cgwc-pv48-fhj5 , PYSEC-2026-3032 , EUVD-2026-56859

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi python-engineio 4.13.2
  • python-engineio Debian 14 4.14.0-1

debian advisories DEBIAN-CVE-2026-48802

  • python-python-engineio SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Python 3 15 SP7 4.3.4-150600.3.3.1

suse advisories SUSE-SU-2026:3085-1

  • python-python-engineio openSUSE Leap 16.0 4.12.0-bp160.2.1

opensuse advisories openSUSE-SU-2026:21182-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-48802 updated cvss 7.5

engineio: python-engineio: Denial of Service via unbound thread allocation in heartbeat mechanism.

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi python-engineio
<4.13.2
4.13.2

Affected products

  • miguelgrinberg python-engineio

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.