CVE-2026-34518: Aiohttp AIOHTTP Leaks Cookie And Proxy-Authorization Vulnerability

LOW
Advisory Identifier: GHSA-966j-vmvw-g2g9
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CVSS 5.3
CWE-200
Published
Advisory Summary

CVE-2026-34518 is a LOW (CVSS 5.3) aiohttp leaks cookie and proxy-authorization vulnerability (CWE-200: Exposure of Sensitive Information to an Unauthorized Actor) affecting Aiohttp libraries in the PyPI ecosystem. The issue involves aiohttp leaks cookie and proxy-authorization headers on cross-origin redirect. Remediation is available by upgrading affected packages to version 3.13.4.

CVE-2026-34518 at a Glance

CVE Identifier CVE-2026-34518
GHSA Identifier GHSA-966j-vmvw-g2g9
Severity LOW
CVSS v3.1 Base Score 5.3
CWE Classification CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
Affected Product Aiohttp
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.3

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:L/I:N/A:N).

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 Low (C:L)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-34518

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: 3.13.4 
pip install aiohttp>=3.13.4
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-2026-34518, 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 3.13.4), 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-200: Exposure of Sensitive Information to an Unauthorized Actor, where the product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. 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 When following redirects to a different origin, aiohttp drops the Authorization header, but retains the Cookie and Proxy-Authorization headers. ### Impact The Cookie and Proxy-Authorizations headers could contain sensitive information which may be leaked to an unintended party after following a redirect. ----- Patch: https://github.com/aio-libs/aiohttp/commit/5351c980dcec7ad385730efdf4e1f4338b24fdb6

CVE-2026-34518 Affected Aiohttp Versions

1 component(s)
Fixed Versions:
3.13.4
Product / Package Ecosystem Affected Versions Fixed Version
aiohttp
pypi/aiohttp
PyPI
< 3.13.4
3.13.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-966j-vmvw-g2g9
NVD — CVE-2026-34518 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34518
Security Fix Commit FIX COMMIT
https://github.com/aio-libs/aiohttp/commit/5351c980dcec7ad385730efdf4e1f4338b24fdb6
Aiohttp Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp
Aiohttp Release RELEASE
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4

Frequently Asked Questions

What is CVE-2026-34518?
CVE-2026-34518 is a security vulnerability in Aiohttp involving AIOHTTP leaks Cookie and Proxy-Authorization headers on cross-origin redirect under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.
Which Aiohttp versions are affected?
Affected versions include releases prior to 3.13.4 across affected packages: aiohttp.
What version fixes CVE-2026-34518?
Upgrading to 3.13.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is aiohttp affected?
Yes, aiohttp is affected in releases prior to 3.13.4. Upgrade your dependency to 3.13.4 or later.
What is the CVSS score of CVE-2026-34518?
CVE-2026-34518 has a CVSS v3.1 base score of 5.3 (LOW) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2026-34518?
CVE-2026-34518 is classified under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor (The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.).
How can I check PyPI dependencies for CVE-2026-34518?
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-966j-vmvw-g2g9",
  "modified" : "2026-04-24T20:33:18Z",
  "published" : "2026-04-01T21:47:46Z",
  "aliases" : [ "CVE-2026-34518" ],
  "summary" : "AIOHTTP leaks Cookie and Proxy-Authorization headers on cross-origin redirect",
  "details" : "### Summary\n\nWhen following redirects to a different origin, aiohttp drops the Authorization header, but retains the Cookie and Proxy-Authorization headers.\n\n### Impact\n\nThe Cookie and Proxy-Authorizations headers could contain sensitive information which may be leaked to an unintended party after following a redirect.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/5351c980dcec7ad385730efdf4e1f4338b24fdb6",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "aiohttp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.13.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.13.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/security/advisories/GHSA-966j-vmvw-g2g9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34518"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/commit/5351c980dcec7ad385730efdf4e1f4338b24fdb6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/aio-libs/aiohttp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-01T21:47:46Z",
    "nvd_published_at" : "2026-04-01T21:17:00Z"
  }
}