Request smuggling via conflicting framing headers
Published Sep 2, 2026 · Updated Sep 2, 2026
HTTP request smuggling in Pydantic HTTPX2 before 2.11.0 allows remote attackers to desynchronize HTTP/1.1 connections. Request._prepare() applies body-derived defaults independently with setdefault(), adding Content-Length when the caller supplied Transfer-Encoding. Exploitation requires attacker-controlled framing and body data plus intermediaries that disagree on message boundaries, enabling routing or authorization bypass and response or cache poisoning.
Summary
What happened
HTTP request smuggling in Pydantic HTTPX2 before 2.11.0 allows remote attackers to desynchronize HTTP/1.1 connections. Request._prepare() applies body-derived defaults independently with setdefault(), adding Content-Length when the caller supplied Transfer-Encoding. Exploitation requires attacker-controlled framing and body data plus intermediaries that disagree on message boundaries, enabling routing or authorization bypass and response or cache poisoning.
The record
- CVE
- CVE-2026-84380
- Published
- Sep 2, 2026
- Updated
- Sep 2, 2026
- Vendor
- Pydantic
- Product
- HTTPX2
- Classifications
- CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 2, 2026CVE publishedPublication date reported by the CVE source.
- Sep 2, 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=< 2.11.0
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
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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