What versions of AIOHTTP are affected by these vulnerabilities?

AIOHTTP versions 3.9.5 and earlier are affected by these vulnerabilities. It is recommended to upgrade to version 3.13.4 or later to mitigate the risks.

How do I upgrade AIOHTTP to the latest version?

You can upgrade AIOHTTP using pip, the Python package installer. Run the command `pip install --upgrade aiohttp` in your terminal to upgrade to the latest version.

What are the potential impacts of these AIOHTTP vulnerabilities?

The vulnerabilities in AIOHTTP could lead to header injection, denial-of-service (DoS), and memory exhaustion. These issues can compromise the security and availability of applications using AIOHTTP.

AIOHTTP Patches Multiple Vulnerabilities (CVE-2026-34520 et al.)

Q: What is AIOHTTP?

AIOHTTP is an asynchronous HTTP client/server framework for Python, built on top of asyncio. It's designed for building high-performance web applications and services. AIOHTTP supports both client-side requests and server-side responses, making it a versatile tool for network programming.

Multiple vulnerabilities have been discovered in AIOHTTP, potentially leading to header injection, denial-of-service (DoS), and memory exhaustion. These issues affect applications using AIOHTTP version 3.9.5 and earlier. A patch is available in version 3.13.4.

These vulnerabilities range in severity, with the header injection issue having a CVSS score of 2.5.

What is Aiohttp?

Aiohttp is a popular asynchronous HTTP client/server framework for Python, built on top of asyncio. It's commonly used for building high-performance web applications and services. Aiohttp provides both client and server functionalities, allowing developers to create robust and scalable network applications. To learn more, search all aiohttp CVEs.

CVE-2026-34520: AIOHTTP Header Injection Vulnerability

CVSS2.5

Affected versionsAIOHTTP versions 3.9.5 and earlier are affected. This vulnerability exists because the C parser does not properly sanitize header values.

Low severity due to limited impact and exploitability.

EPSS score of 0.045 indicates a low probability of exploitation.

AIOHTTP's C parser (llhttp) accepted null bytes and control characters in response header values. An attacker could send crafted header values that are interpreted differently than expected, potentially leading to security bypasses.

How to fix CVE-2026-34520 in Aiohttp

Patch within 7 days

1.Upgrade AIOHTTP to version 3.13.4 or later.

Upgrade AIOHTTP

pip install --upgrade aiohttp

Verify with:

verify

pip show aiohttp

Workaround: Implement input validation and sanitization on header values at the application level.

NextGuard automatically flags CVE-2026-34520 if Aiohttp appears in any of your monitored projects — no manual lookup required.

CVE-2026-34516: AIOHTTP Multipart Header Size Bypass

CVSSN/A

Affected versionsAIOHTTP versions 3.9.5 and earlier are affected. Applications processing multipart requests are particularly vulnerable.

Severity not specified.

EPSS score of 0.04 indicates a low probability of exploitation.

AIOHTTP allowed an excessive number of multipart headers, potentially leading to a denial-of-service (DoS) vulnerability. Multipart headers were not subject to the same size restrictions as normal headers.

How to fix CVE-2026-34516 in Aiohttp

Patch within 7 days

1.Upgrade AIOHTTP to version 3.13.4 or later.

Upgrade AIOHTTP

pip install --upgrade aiohttp

Verify with:

verify

pip show aiohttp

Workaround: Limit the number of multipart headers accepted by the application.

NextGuard automatically flags CVE-2026-34516 if Aiohttp appears in any of your monitored projects — no manual lookup required.

CVE-2026-22815: AIOHTTP Uncapped Memory Usage via Trailer Headers

CVSSN/A

Affected versionsAIOHTTP versions 3.9.5 and earlier are affected. Applications that process requests or responses with trailer headers are vulnerable.

Severity not specified.

EPSS score of 0.04 indicates a low probability of exploitation.

AIOHTTP allowed unlimited trailer headers, potentially leading to uncapped memory usage and a denial-of-service (DoS). Insufficient restrictions in header/trailer handling could cause memory exhaustion.

How to fix CVE-2026-22815 in Aiohttp

Patch within 7 days

1.Upgrade AIOHTTP to version 3.13.4 or later.

Upgrade AIOHTTP

pip install --upgrade aiohttp

Verify with:

verify

pip show aiohttp

Workaround: Implement limits on the number and size of trailer headers accepted by the application.

NextGuard automatically flags CVE-2026-22815 if Aiohttp appears in any of your monitored projects — no manual lookup required.

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Frequently asked questions

Multiple vulnerabilities in AIOHTTP have been addressed in version 3.13.4. It is crucial to upgrade to the latest version to protect your applications. See all python vulnerabilities.