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Fencer Vulns
high 7.5

CVE-2026-34824 json

Mesop: Unbounded Thread Creation in WebSocket Handler Leads to Denial of Service

published 2026-04-03 7 mo ago modified 2026-07-24 3 mo ago also EUVD-2026-18909 , GHSA-3jr7-6hqp-x679 , PYSEC-2026-2204

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

Mesop is a Python-based UI framework that allows users to build web applications. From version 1.2.3 to before version 1.2.5, an uncontrolled resource consumption vulnerability exists in the WebSocket implementation of the Mesop framework. An unauthenticated attacker can send a rapid succession of WebSocket messages, forcing the server to spawn an unbounded number of operating system threads. This leads to thread exhaustion and Out of Memory (OOM) errors, causing a complete Denial of Service (DoS) for any application built on the framework. This issue has been patched in version 1.2.5.

Patch / fix

  • pypi mesop 1.2.5
  • mesop-dev mesop 1.2.5

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.75% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/mesop-dev/mesop/security/advisories/GHSA-3jr7-6hqp-x679 referenced PoC, tagged "exploit" by a source, unverified

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 mesop
>=1.2.3, <1.2.5
1.2.5

Affected products

  • mesop-dev mesop

Classification

Weakness
  • CWE-125 Out-of-bounds Read
  • CWE-400 Uncontrolled Resource Consumption
  • 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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.