CVE-2026-48710
Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks
Description
Starlette is a lightweight ASGI framework/toolkit. Prior to version 1.0.1, the HTTP `Host` request header was not validated before being used to reconstruct `request.url`. Because the routing algorithm relies on the raw HTTP path while `request.url` is rebuilt from the `Host` header, a malformed header could make `request.url.path` differ from the path that was actually requested. Middleware and endpoints that apply security restrictions based on `request.url` (rather than the raw `scope` path) could therefore be bypassed. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the `Host` header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing `request.url` and falls back to `scope["server"]` for malformed values.
CVSS Vector Breakdown
AV:NAttack VectorAC:LAttack ComplexityPR:NPrivileges RequiredUI:NUser InteractionS:UScopeC:LConfidentialityI:LIntegrityA:NAvailabilityWeaknesses
Affected Products
Exploitability
Attack Graph
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MITRE ATT&CK
1 techniqueReferences
- LiteLLM Flaw CVE-2026-42271 Exploited in the Wild, Chains to Unauthenticated RCEen·The Hacker News· Exploited BerriAI LiteLLM ai-ml
- BadHost vulnerability bypasses authentication on AI infrastructureen·Risky Business News· Patch Starlette (BadHost, CVE-2026-48710) auth-bypass
- Millions of AI agents imperiled by critical vulnerability in open source packageen·Ars Technica (Security)· Patch Starlette supply-chain
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