CVE-2023-37276
MEDIUMaiohttp vulnerable to HTTP request smuggling
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
aiohttpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. aiohttp v3.8.4 and earlier are bundled with llhttp v6.0.6. Vulnerable code is used by aiohttp for its HTTP request parser when available which is the default case when installing from a wheel. This vulnerability only affects users of aiohttp as an HTTP server (ie aiohttp.Application), you are not affected by this vulnerability if you are using aiohttp as an HTTP client library (ie aiohttp.ClientSession). Sending a crafted HTTP request will cause the server to misinterpret one of the HTTP header values leading to HTTP request smuggling. This issue has been addressed in version 3.8.5. Users are advised to upgrade. Users unable to upgrade can reinstall aiohttp using AIOHTTP_NO_EXTENSIONS=1 as an environment variable to disable the llhttp HTTP request parser implementation. The pure Python implementation isn't vulnerable.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | aiohttp | all versions | 3.8.5 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aiohttp. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update aiohttp to 3.8.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-37276 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2023-37276 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2023-37276. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-37276 in your dependencies?
O3 detects CVE-2023-37276 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.