HTTP Response Splitting Affecting aiohttp package, versions [,3.13.4)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-AIOHTTP-15873704
- published2 Apr 2026
- disclosed1 Apr 2026
- creditvmfunc, oxqnd
Introduced: 1 Apr 2026
NewCVE-2026-34520 (opens in a new tab)How to fix?
Upgrade aiohttp to version 3.13.4 or higher.
Overview
Affected versions of this package are vulnerable to HTTP Response Splitting in the llhttp component. An attacker can manipulate HTTP response headers by injecting null bytes or control characters, causing headers to be interpreted differently by various components, which may lead to security bypass or inconsistent behavior between the application and reverse proxies.