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High, CVSS 7.5amended

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

CVE-2026-34824GHSA-3jr7-6hqp-x679

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mesop 1.2.5), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI mesop

    Affected
    >= 1.2.3, < 1.2.5
    Fixed in
    1.2.5

Sources

Severity and exploitation
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-2026-34824: 0.75% estimated exploitation activity in the next 30 days; percentile 55.00 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary 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. Details The vulnerability stems from an architectural flaw in how incoming WebSocket messages are processed. In the mesop/server/server.py file, the handlewebsocket function listens for incoming messages and immediately spawns a new threading.Thread for every successfully parsed uirequest. There is no thread pool, message queue, or rate-limiting mechanism implemented to restrict the number of concurrent threads spawned per connection. Vulnerable code snippet in mesop/server/server.py: PoC To reproduce this vulnerability, you only need a running instance of a…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-3jr7-6hqp-x679

  2. Revision 1 · created ·

    Published from osv record GHSA-3jr7-6hqp-x679

Agent brief

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# Patch Next advisory brief: CVE-2026-34824

Advisory: Mesop: Unbounded Thread Creation in WebSocket Handler Leads to Denial of Service
IDs: CVE-2026-34824, GHSA-3jr7-6hqp-x679
Record: https://patchnext.com/advisories/cve-2026-34824 (revision 2, source checked 26 Oct 2026, 13:40 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: mesop 1.2.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mesop: affected >= 1.2.3, < 1.2.5; fixed in 1.2.5

## Suggested inspection (read-only)
- `python -m pip show mesop`: 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 mesop.
- 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-3jr7-6hqp-x679 (OSV record GHSA-3jr7-6hqp-x679 lists affected ranges: PyPI mesop >=1.2.3 <1.2.5 (fixed))
- Verified: https://github.com/advisories/GHSA-3jr7-6hqp-x679 (GitHub-reviewed advisory GHSA-3jr7-6hqp-x679 lists affected ranges: PyPI mesop >=1.2.3 <1.2.5)

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