Authentication bypass via malformed Host header reparsing
Published May 26, 2026 · Updated May 26, 2026
Host-header validation failure in Kludex Starlette before 1.0.1 allows remote attackers to bypass path-based security checks. URL construction concatenates the unvalidated Host header with the ASGI scope path and reparses it, so delimiters such as ?, /, or # make request.url.path differ from the route that executes. Exposure requires security-sensitive code to trust request.url or request.url.path and a frontend that forwards malformed attacker-controlled host values.
Summary
What happened
Host-header validation failure in Kludex Starlette before 1.0.1 allows remote attackers to bypass path-based security checks. URL construction concatenates the unvalidated Host header with the ASGI scope path and reparses it, so delimiters such as ?, /, or # make request.url.path differ from the route that executes. Exposure requires security-sensitive code to trust request.url or request.url.path and a frontend that forwards malformed attacker-controlled host values.
The record
- CVE
- CVE-2026-48710
- Published
- May 26, 2026
- Updated
- May 26, 2026
- Vendor
- Kludex
- Product
- Starlette
- Classifications
- CWE-436, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 26, 2026CVE publishedPublication date reported by the CVE source.
- May 26, 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?
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- Affected versionversion=< 1.0.1
What conditions does exploitation require?
What is affected?
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.
Public exploit references
- Starlette malformed-Host authentication-bypass proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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