CVE-2026-34519 AIOHTTP: HTTP response splitting via \r in reason phrase
Attackers can inject headers via the reason phrase in aiohttp responses, potentially leading to cache poisoning or XSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-34519?
CVE-2026-34519 is a low-severity vulnerability in aio-libs aiohttp, published on 1 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, an attacker who controls the reason parameter when creating a Response may be able to inject extra headers or similar exploits. This issue has been patched in version 3.13.4.
Weakness: CWE-113
Which versions are affected by CVE-2026-34519?
3 open source packages ship an affected version, including aiohttp. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
aiohttp PyPI | All versions | 3.13.4 |
aiohttp PyPI | All versions | 3.13.4 |
aiohttp PyPI | All versions | 3.13.4 |
Products include Aiohttp Aiohttp.
How do I fix CVE-2026-34519?
Upgrade aiohttp to 3.13.4 or later.
Is CVE-2026-34519 being exploited?
There is no known exploitation of CVE-2026-34519 in the wild and no public exploit code.
Other vulnerabilities in aio-libs aiohttp
- CVE-2024-52303 aiohttp memory leak when middleware is enabled when requesting a resource with a non-allowed method
- CVE-2025-69223 AIOHTTP's HTTP Parser auto_decompress feature is vulnerable to zip bomb
- CVE-2024-30251 Denial of service when trying to parse malformed POST requests in aiohttp
- CVE-2023-49081 aiohttp's ClientSession is vulnerable to CRLF injection via version
- CVE-2026-22815 AIOHTTP: Uncapped memory usage possible through aiohttp allowing unlimited trailer headers
Sources
Also known as AZL-81776, CLEANSTART-2026-QH05676, CLEANSTART-2026-UK00522, DEBIAN-CVE-2026-34519, ECHO-abe8-b546-ad42, GHSA-mwh4-6h8g-pg8w and 10 more.