CVE-2026-54277 AIOHTTP: C HTTP Parser Bypasses max_line_size for Fragmented Lines
Attackers can cause denial of service by sending oversized HTTP lines that bypass memory limits in the default C parser.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54277?
CVE-2026-54277 is a medium-severity denial of service vulnerability in aio-libs aiohttp, published on 22 Jun 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 3.14.1, it is possible to bypass the max_line_size check in parts of an HTTP request in the C parser. 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. This vulnerability is fixed in 3.14.1.
Weakness: CWE-770
Which versions are affected by CVE-2026-54277?
3 open source packages ship an affected version, including aiohttp. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
aiohttp PyPI | All versions | 3.14.1 |
aiohttp PyPI | All versions | 3.14.1 |
aiohttp PyPI | All versions | 3.14.1 |
Products include Aiohttp Aiohttp.
How do I fix CVE-2026-54277?
Upgrade aiohttp to 3.14.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-54277 being exploited?
There is no known exploitation of CVE-2026-54277 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-90671, CLEANSTART-2026-JS34043, CLEANSTART-2026-TM43403, DEBIAN-CVE-2026-54277, ECHO-c85b-77dd-0d28, GHSA-63hw-fmq6-xxg2 and 20 more.