CVE-2026-48809: Python engineio Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-m9gh-vj53-gvh9
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CVSS 7.5
CWE-770
Published
Advisory Summary

CVE-2026-48809 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Python engineio libraries in the PyPI ecosystem. The issue involves python-engineio has possible denial of service due to maximum payload size sometimes not being enforced. Remediation is available by upgrading affected packages to version 4.13.2.

CVE-2026-48809 at a Glance

CVE Identifier CVE-2026-48809
GHSA Identifier GHSA-m9gh-vj53-gvh9
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Python engineio
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-48809

To remediate this vulnerability, upgrade all affected Python engineio dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

python-engineio fixed: 4.13.2 
pip install python-engineio>=4.13.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show python-engineio

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-48809, inspect your installed packages using pip:

pip show python-engineio

Analyze the terminal output to locate any version of Python engineio in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.13.2), your application is affected.

Note: The pip show python-engineio command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Python engineio, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact There are two specific configurations of the python-engineio server in which the size of incoming messages is not checked before the messages are loaded into memory. An attacker can take advantage of these to cause unnecessary memory allocations in the python-engineio server. The two cases are: - POST requests, when using ASGI with the long polling transport - WebSocket messages, when using Aiohttp with the WebSocket transport ### Patches Version 4.13.2 addresses this issue as follows: - ASGI severs now only load the body of incoming requests into memory after the client is confirmed to be known and authenticated, and the payload size is below the maximum allowed size. Requests that do not comply with these requirements are discarded. - Aiohttp servers configure the maximum payload size in the underlying WebSocket layer from Aiohttp, so that large messages are discarded by Aiohttp before they are delivered to python-engineio.

CVE-2026-48809 Affected Python engineio Versions

1 component(s)
Fixed Versions:
4.13.2
Product / Package Ecosystem Affected Versions Fixed Version
python-engineio
pypi/python-engineio
PyPI
< 4.13.2
4.13.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-m9gh-vj53-gvh9
Python engineio Source Repository REPOSITORY
https://github.com/miguelgrinberg/python-engineio

Frequently Asked Questions

What is CVE-2026-48809?
CVE-2026-48809 is a security vulnerability in Python engineio involving python-engineio has possible denial of service due to maximum payload size sometimes not being enforced under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Python engineio versions are affected?
Affected versions include releases prior to 4.13.2 across affected packages: python-engineio.
What version fixes CVE-2026-48809?
Upgrading to 4.13.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is python-engineio affected?
Yes, python-engineio is affected in releases prior to 4.13.2. Upgrade your dependency to 4.13.2 or later.
What is the CVSS score of CVE-2026-48809?
CVE-2026-48809 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-48809?
CVE-2026-48809 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check PyPI dependencies for CVE-2026-48809?
Run the dependency tree command: 'pip show python-engineio'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m9gh-vj53-gvh9",
  "modified" : "2026-06-26T20:48:18Z",
  "published" : "2026-06-26T20:48:18Z",
  "aliases" : [ "CVE-2026-48809" ],
  "summary" : "python-engineio has possible denial of service due to maximum payload size sometimes not being enforced",
  "details" : "### Impact\nThere are two specific configurations of the python-engineio server in which the size of incoming messages is not checked before the messages are loaded into memory. An attacker can take advantage of these to cause unnecessary memory allocations in the python-engineio server. The two cases are:\n\n- POST requests, when using ASGI with the long polling transport\n- WebSocket messages, when using Aiohttp with the WebSocket transport\n\n### Patches\nVersion 4.13.2 addresses this issue as follows:\n\n- ASGI severs now only load the body of incoming requests into memory after the client is confirmed to be known and authenticated, and the payload size is below the maximum allowed size. Requests that do not comply with these requirements are discarded.\n- Aiohttp servers configure the maximum payload size in the underlying WebSocket layer from Aiohttp, so that large messages are discarded by Aiohttp before they are delivered to python-engineio.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "python-engineio"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.13.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.13.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-m9gh-vj53-gvh9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/miguelgrinberg/python-engineio"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T20:48:18Z",
    "nvd_published_at" : null
  }
}