CVE-2023-47627Public exploitNetwork attack vector

Request smuggling via lenient HTTP header parsing

Published Nov 14, 2023 · Updated Nov 3, 2025

HTTP request smuggling in aio-libs aiohttp before 3.8.6 allows remote attackers to alter request routing via malformed headers. The pure-Python parser in aiohttp/http_parser.py accepts signed or underscored Content-Length values, forbidden NUL, CR, or LF bytes in field values, and whitespace before field-name colons. Exposure requires an aiohttp server using the pure-Python parser through AIOHTTP_NO_EXTENSIONS or an installation without the prebuilt extension; divergent parsing can inject a second request into a proxied connection.

CVSS severity7.5
High
EPSS probability0.86%
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 aio-libs aiohttp before 3.8.6 allows remote attackers to alter request routing via malformed headers. The pure-Python parser in aiohttp/http_parser.py accepts signed or underscored Content-Length values, forbidden NUL, CR, or LF bytes in field values, and whitespace before field-name colons. Exposure requires an aiohttp server using the pure-Python parser through AIOHTTP_NO_EXTENSIONS or an installation without the prebuilt extension; divergent parsing can inject a second request into a proxied connection.

The record

CVE
CVE-2023-47627
Published
Nov 14, 2023
Updated
Nov 3, 2025
Vendor
aio-libs
Product
aiohttp
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 14, 2023CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record 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=< 3.8.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

aio-libs · aiohttpversion=< 3.8.6

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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