CVE-2026-59881: AIOHTTP WebSocket Client Accepts Compressed Frames Vulnerability

MODERATE
Advisory Identifier: GHSA-mq44-7p77-q5h7
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CWE-20
Published
Advisory Summary

CVE-2026-59881 is a MODERATE websocket client accepts compressed frames vulnerability (CWE-20: Improper Input Validation) affecting AIOHTTP libraries in the PyPI ecosystem. The issue involves websocket client accepts compressed frames without negotiated permessage-deflate. Remediation is available by upgrading affected packages to version 3.14.2.

CVE-2026-59881 at a Glance

CVE Identifier CVE-2026-59881
GHSA Identifier GHSA-mq44-7p77-q5h7
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-20: Improper Input Validation
Affected Product AIOHTTP
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-59881

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

aiohttp fixed: 3.14.2 
pip install aiohttp>=3.14.2
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 aiohttp

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-59881, inspect your installed packages using pip:

pip show aiohttp

Analyze the terminal output to locate any version of AIOHTTP in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.14.2), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In AIOHTTP, 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

### Summary The client accepts and decompresses frames with the RSV1 bit set even when the `permessage-deflate` extension was not negotiated. ### Impact A client may unexpectedly decompress WebSocket frames when explicitly opted out. This could lead to additional CPU/memory consumption, but is unlikely to be a significant issue unless a zip bomb vulnerability or similar is also present. --- Patch: https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6

CVE-2026-59881 Affected AIOHTTP Versions

1 component(s)
Fixed Versions:
3.14.2
Product / Package Ecosystem Affected Versions Fixed Version
aiohttp
pypi/aiohttp
PyPI
< 3.14.2
3.14.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mq44-7p77-q5h7
NVD — CVE-2026-59881 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59881
AIOHTTP Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp/pull/12978
Security Fix Commit FIX COMMIT
https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6
AIOHTTP Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp
AIOHTTP Release RELEASE
http://github.com/aio-libs/aiohttp/releases/tag/v3.14.2

Frequently Asked Questions

What is CVE-2026-59881?
CVE-2026-59881 is a security vulnerability in AIOHTTP involving WebSocket client accepts compressed frames without negotiated permessage-deflate under CWE-20: Improper Input Validation.
Which AIOHTTP versions are affected?
Affected versions include releases prior to 3.14.2 across affected packages: aiohttp.
What version fixes CVE-2026-59881?
Upgrading to 3.14.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is aiohttp affected?
Yes, aiohttp is affected in releases prior to 3.14.2. Upgrade your dependency to 3.14.2 or later.
What CWE is associated with CVE-2026-59881?
CVE-2026-59881 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check PyPI dependencies for CVE-2026-59881?
Run the dependency tree command: 'pip show aiohttp'. 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-mq44-7p77-q5h7",
  "modified" : "2026-08-03T20:40:55Z",
  "published" : "2026-08-03T20:40:55Z",
  "aliases" : [ "CVE-2026-59881" ],
  "summary" : "AIOHTTP: WebSocket client accepts compressed frames without negotiated permessage-deflate",
  "details" : "### Summary\n\nThe client accepts and decompresses frames with the RSV1 bit set even when the `permessage-deflate` extension was not negotiated.\n\n### Impact\n\nA client may unexpectedly decompress WebSocket frames when explicitly opted out. This could lead to additional CPU/memory consumption, but is unlikely to be a significant issue unless a zip bomb vulnerability or similar is also present.\n\n---\n\nPatch: https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "aiohttp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.14.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.14.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mq44-7p77-q5h7"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59881"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/pull/12978"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/aio-libs/aiohttp"
  }, {
    "type" : "WEB",
    "url" : "http://github.com/aio-libs/aiohttp/releases/tag/v3.14.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-03T20:40:55Z",
    "nvd_published_at" : "2026-07-30T19:18:33Z"
  }
}