CVE-2026-54278: aiohttp Unread Compressed Request Bodies Bypass Vulnerability

MODERATE
Advisory Identifier: GHSA-g3cq-j2xw-wf74
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CWE-409
Published
Advisory Summary

CVE-2026-54278 is a MODERATE unread compressed request bodies bypass vulnerability (CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)) affecting aiohttp libraries in the PyPI ecosystem. The issue involves unread compressed request bodies bypass client_max_size during cleanup. Remediation is available by upgrading affected packages to version 3.14.1.

CVE-2026-54278 at a Glance

CVE Identifier CVE-2026-54278
GHSA Identifier GHSA-g3cq-j2xw-wf74
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)
Affected Product aiohttp
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-54278

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: 3.14.1 
pip install aiohttp>=3.14.1
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-2026-54278, 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 3.14.1), 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-409: Improper Handling of Highly Compressed Data (Data Amplification), where the product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. 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 During cleanup it is possible for a compressed request body to be decompressed into memory in one chunk. ### Impact An attacker may be able to send a compressed payload in specific situations that could be decompressed into memory, potentially leading to DoS (a zip bomb edge case). ### Workaround Disable compression if unable to upgrade. ----- Patch: https://github.com/aio-libs/aiohttp/commit/4f7480e474cccc6a8cc2c92ad3f17a31dedf8232

CVE-2026-54278 Affected aiohttp Versions

1 component(s)
Fixed Versions:
3.14.1
Product / Package Ecosystem Affected Versions Fixed Version
aiohttp
pypi/aiohttp
PyPI
< 3.14.1
3.14.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-g3cq-j2xw-wf74
aiohttp Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp

Frequently Asked Questions

What is CVE-2026-54278?
CVE-2026-54278 is a security vulnerability in aiohttp involving Unread Compressed Request Bodies Bypass client_max_size During Cleanup under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification).
Which aiohttp versions are affected?
Affected versions include releases prior to 3.14.1 across affected packages: aiohttp.
What version fixes CVE-2026-54278?
Upgrading to 3.14.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is aiohttp affected?
Yes, aiohttp is affected in releases prior to 3.14.1. Upgrade your dependency to 3.14.1 or later.
What CWE is associated with CVE-2026-54278?
CVE-2026-54278 is classified under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) (The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.).
How can I check PyPI dependencies for CVE-2026-54278?
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-g3cq-j2xw-wf74",
  "modified" : "2026-06-15T20:09:51Z",
  "published" : "2026-06-15T20:09:51Z",
  "aliases" : [ "CVE-2026-54278" ],
  "summary" : "aiohttp: Unread Compressed Request Bodies Bypass client_max_size During Cleanup",
  "details" : "### Summary\n\nDuring cleanup it is possible for a compressed request body to be decompressed into memory in one chunk.\n\n### Impact\n\nAn attacker may be able to send a compressed payload in specific situations that could be decompressed into memory, potentially leading to DoS (a zip bomb edge case).\n\n### Workaround\n\nDisable compression if unable to upgrade.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/4f7480e474cccc6a8cc2c92ad3f17a31dedf8232",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "aiohttp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.14.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.14.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/security/advisories/GHSA-g3cq-j2xw-wf74"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/aio-libs/aiohttp"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-409" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-15T20:09:51Z",
    "nvd_published_at" : null
  }
}