HTTP request smuggling via unvalidated method
Published Nov 29, 2023 · Updated Jun 23, 2026
CRLF injection in aiohttp ClientSession before 3.9.0 allows remote attackers to alter outbound HTTP requests through a controlled method. ClientRequest accepted the method string without token validation and serialized embedded CRLF characters into the request line, enabling injected headers or a second request. Exploitation requires a consuming application to pass attacker-controlled method values; successful injection can smuggle requests to the destination server.
Summary
What happened
CRLF injection in aiohttp ClientSession before 3.9.0 allows remote attackers to alter outbound HTTP requests through a controlled method. ClientRequest accepted the method string without token validation and serialized embedded CRLF characters into the request line, enabling injected headers or a second request. Exploitation requires a consuming application to pass attacker-controlled method values; successful injection can smuggle requests to the destination server.
The record
- CVE
- CVE-2023-49082
- Published
- Nov 29, 2023
- Updated
- Jun 23, 2026
- Vendor
- aio-libs
- Product
- aiohttp
- Classifications
- CWE-93, CWE-20
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Nov 29, 2023CVE publishedPublication date reported by the CVE source.
- Jun 23, 2026Record 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.
- Affected versionversion=< 3.9.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- aiohttp CRLF proof of conceptproof of concept · demonstrated
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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