CVE-2026-34520
AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
Description
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.
INFO
Published Date :
April 1, 2026, 9:17 p.m.
Last Modified :
April 16, 2026, 4:24 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | CRITICAL | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | ||||
| CVSS 4.0 | LOW | [email protected] |
Solution
- Update aiohttp to version 3.13.4 or later.
- Configure proper input validation for headers.
Public PoC/Exploit Available at Github
CVE-2026-34520 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-34520.
| URL | Resource |
|---|---|
| https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 | Patch |
| https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 | Release Notes |
| https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf | Patch Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-34520 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-34520
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
An agentic approach to triage ACS_CVSS_CRITICAL JIRA tickets
Python
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-34520 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-34520 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 16, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:aiohttp:aiohttp:*:*:*:*:*:*:*:* versions up to (excluding) 3.13.4 Added Reference Type GitHub, Inc.: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 Types: Release Notes Added Reference Type GitHub, Inc.: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf Types: Patch, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 04, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H -
New CVE Received by [email protected]
Apr. 01, 2026
Action Type Old Value New Value Added Description AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-113 Added Reference https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 Added Reference https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 Added Reference https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf