CVE-2026-54277: aiohttp C HTTP Parser Bypasses Max_line_size Vulnerability

MODERATE
Advisory Identifier: GHSA-63hw-fmq6-xxg2
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CWE-770
Published
Advisory Summary

CVE-2026-54277 is a MODERATE c http parser bypasses max_line_size vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting aiohttp libraries in the PyPI ecosystem. The issue involves c http parser bypasses max_line_size for fragmented lines. Remediation is available by upgrading affected packages to version 3.14.1.

CVE-2026-54277 at a Glance

CVE Identifier CVE-2026-54277
GHSA Identifier GHSA-63hw-fmq6-xxg2
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product aiohttp
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-54277

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-2026-54277, 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-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 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 It is possible to bypass the max_line_size check in parts of an HTTP request in the C parser. ### Impact If using the optimised C parser (the default in pre-built wheels), then an attacker may be able to send oversized lines through the HTTP parser and use an excessive amount of memory, potentially leading to DoS. ----- Patch: https://github.com/aio-libs/aiohttp/commit/5ab61bb4cd88f19b712f12c7c9295fe262bf804d

CVE-2026-54277 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-63hw-fmq6-xxg2
Security Fix Commit FIX COMMIT
https://github.com/aio-libs/aiohttp/commit/5ab61bb4cd88f19b712f12c7c9295fe262bf804d
aiohttp Source Repository REPOSITORY
https://github.com/aio-libs/aiohttp

Frequently Asked Questions

What is CVE-2026-54277?
CVE-2026-54277 is a security vulnerability in aiohttp involving C HTTP Parser Bypasses max_line_size for Fragmented Lines under CWE-770: Allocation of Resources Without Limits or Throttling.
Which aiohttp versions are affected?
Affected versions include releases prior to 3.14.1 across affected packages: aiohttp.
What version fixes CVE-2026-54277?
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-2026-54277?
CVE-2026-54277 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-2026-54277?
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-63hw-fmq6-xxg2",
  "modified" : "2026-06-15T20:09:16Z",
  "published" : "2026-06-15T20:09:16Z",
  "aliases" : [ "CVE-2026-54277" ],
  "summary" : "aiohttp: C HTTP Parser Bypasses max_line_size for Fragmented Lines",
  "details" : "### Summary\n\nIt is possible to bypass the max_line_size check in parts of an HTTP request in the C parser.\n\n### Impact\n\nIf using the optimised C parser (the default in pre-built wheels), then an attacker may be able to send oversized lines through the HTTP parser and use an excessive amount of memory, potentially leading to DoS.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/5ab61bb4cd88f19b712f12c7c9295fe262bf804d",
  "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-63hw-fmq6-xxg2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/aio-libs/aiohttp/commit/5ab61bb4cd88f19b712f12c7c9295fe262bf804d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/aio-libs/aiohttp"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-15T20:09:16Z",
    "nvd_published_at" : null
  }
}