CVE-2026-54275: aiohttp TLS Server Hostname Override Is Vulnerability

LOW
Advisory Identifier: GHSA-4m7w-qmgq-4wj5
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CWE-297
Published
Advisory Summary

CVE-2026-54275 is a LOW tls server hostname override is vulnerability (CWE-297: Improper Validation of Certificate with Host Mismatch) affecting aiohttp libraries in the PyPI ecosystem. The issue involves tls server hostname override is ignored when reusing https connections. Remediation is available by upgrading affected packages to version 3.14.1.

CVE-2026-54275 at a Glance

CVE Identifier CVE-2026-54275
GHSA Identifier GHSA-4m7w-qmgq-4wj5
Severity LOW
CVSS v3.1 Base Score N/A
CWE Classification CWE-297: Improper Validation of Certificate with Host Mismatch
Affected Product aiohttp
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-54275

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-2026-54275, 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-297: Improper Validation of Certificate with Host Mismatch, where the product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host. 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 `server_hostname` TLS SNI check can be bypassed when an existing connection is reused. ### Impact If an application makes multiple requests to the same domain, but with different per-request `server_hostname` parameters, then the later calls may succeed by reusing the existing connection when they should have been rejected due to the TLS SNI check. ### Workaround Disable keep_alive if you need to change the `server_hostname` check between requests. ----- Patch: https://github.com/aio-libs/aiohttp/commit/0ca2b6c28a25726527a8b60f25960262a91ed0e0

CVE-2026-54275 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-4m7w-qmgq-4wj5
aiohttp Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp

Frequently Asked Questions

What is CVE-2026-54275?
CVE-2026-54275 is a security vulnerability in aiohttp involving TLS Server Hostname Override Is Ignored When Reusing HTTPS Connections under CWE-297: Improper Validation of Certificate with Host Mismatch.
Which aiohttp versions are affected?
Affected versions include releases prior to 3.14.1 across affected packages: aiohttp.
What version fixes CVE-2026-54275?
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-2026-54275?
CVE-2026-54275 is classified under CWE-297: Improper Validation of Certificate with Host Mismatch (The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.).
How can I check PyPI dependencies for CVE-2026-54275?
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-4m7w-qmgq-4wj5",
  "modified" : "2026-06-15T20:11:13Z",
  "published" : "2026-06-15T20:11:13Z",
  "aliases" : [ "CVE-2026-54275" ],
  "summary" : "aiohttp: TLS Server Hostname Override Is Ignored When Reusing HTTPS Connections",
  "details" : "### Summary\n\nThe `server_hostname` TLS SNI check can be bypassed when an existing connection is reused.\n\n### Impact\n\nIf an application makes multiple requests to the same domain, but with different per-request `server_hostname` parameters, then the later calls may succeed by reusing the existing connection when they should have been rejected due to the TLS SNI check.\n\n### Workaround\n\nDisable keep_alive if you need to change the `server_hostname` check between requests.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/0ca2b6c28a25726527a8b60f25960262a91ed0e0",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/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-4m7w-qmgq-4wj5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/aio-libs/aiohttp"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-297" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-15T20:11:13Z",
    "nvd_published_at" : null
  }
}