How severe is CVE-2023-37276?

CVE-2023-37276 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2023-37276 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-37276?

CVE-2023-37276 affects Aiohttp. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2023-37276?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-37276 published?

CVE-2023-37276 was published on 2023-07-19 and last updated on 2026-06-17.

CVE-2023-37276

CVE-2023-37276 is a medium-severity vulnerability in Aiohttp with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-444.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 1% (70th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-444
Affected product: Aiohttp
Published: 2023-07-19
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2023-37276?: 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.
How severe is CVE-2023-37276?: CVE-2023-37276 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2023-37276 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-37276?: CVE-2023-37276 affects Aiohttp. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-37276?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-37276 published?: CVE-2023-37276 was published on 2023-07-19 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:aiohttp:aiohttp:*:*:*:*:*:*:*:*

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