CVE-2023-37276Public exploitNetwork attack vector

HTTP request smuggling via misparsed header carriage return

Published Jul 19, 2023 · Updated Oct 18, 2024

HTTP request smuggling in aiohttp 3.8.4 and earlier allows remote attackers to alter server request parsing via crafted headers. The bundled llhttp 6.0.6 parser treats a carriage return inside a header value as a boundary, promoting trailing bytes into a Transfer-Encoding header. Exposure requires aiohttp.Application server use with the compiled parser, the default for wheel installations; client-only and pure-Python deployments are unaffected.

CVSS severity5.3
Medium
EPSS probability1.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in aiohttp 3.8.4 and earlier allows remote attackers to alter server request parsing via crafted headers. The bundled llhttp 6.0.6 parser treats a carriage return inside a header value as a boundary, promoting trailing bytes into a Transfer-Encoding header. Exposure requires aiohttp.Application server use with the compiled parser, the default for wheel installations; client-only and pure-Python deployments are unaffected.

The record

CVE
CVE-2023-37276
Published
Jul 19, 2023
Updated
Oct 18, 2024
Vendor
aio-libs
Product
aiohttp
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 19, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 18, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.8.5
  2. Affected versionversion=< 3.8.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

aio-libs · aiohttpversion=0 <3.8.5; version=< 3.8.5

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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