6.5 CVE-2026-48710

Enriched by CISA

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.
https://nvd.nist.gov/vuln/detail/CVE-2026-48710

Categories

CWE-444 : Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
The product acts as an intermediary HTTP agent(such as a proxy or firewall) in the data flow between twoentities such as a client and server, but it does notinterpret malformed HTTP requests or responses in ways thatare consistent with how the messages will be processed bythose entities that are at the ultimate destination. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.) Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433]. Use only SSL communication. Terminate the client session after each request. Turn all pages to non-cacheable. SSL/TLS-capable proxy allows HTTP smuggling when used in tandem with HTTP/1.0 services, due to inconsistent interpretation and input sanitization of HTTP messages within the body of another message Chain: caching proxy server has improper input validation (CWE-20) of headers, allowing HTTP response smuggling (CWE-444) using an "LF line ending" Node.js platform allows request smuggling via two Transfer-Encoding headers Web servers allow request smuggling via inconsistent HTTP headers. HTTP server allows request smuggling with both a "Transfer-Encoding: chunked" header and a Content-Length header HTTP server allows request smuggling with both a "Transfer-Encoding: chunked" header and a Content-Length header

References

security-advisories@github.com

https://badhost.org
https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f9...
https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr
https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-202...
https://ostif.org/disclosing-the-badhost-vulnerability-in-starlette
https://www.secwest.net/starlette
https://www.x41-dsec.de/lab/advisories/x41-2026-002-starlette

AFFECTED (from MITRE)

Vendor	Product	Versions
Kludex	starlette	< 1.0.1 [affected]
© 2022 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.

CPE

cpe	start	end

REMEDIATION

EXPLOITS

Exploit-db.com

id	description	date
No known exploits

POC Github

Url
No known exploits

Other Nist (github, ...)

Url
No known exploits

CAPEC

Common Attack Pattern Enumerations and Classifications

id	description	severity
273	HTTP Response Smuggling Modification/manipulation of HTTP message headers, request-line and body parameters to disrupt and interfere in the interpretation and parsing of HTTP message lengths/boundaries for consecutive HTTP messages by HTTP agents in a HTTP chain or network path. [Survey network to identify target] The adversary performs network reconnaissance by monitoring relevant traffic to identify the network path and parsing of the HTTP messages with the goal of identifying potential targets. [Identify vulnerabilities in targeted HTTP infrastructure and technologies] The adversary sends a variety of benign/ambiguous HTTP requests to observe responses from HTTP infrastructure to intended targets in order to identify differences/discrepancies in the interpretation and parsing of HTTP requests by examining supported HTTP protocol versions, message sizes, and HTTP headers. [Cause differential HTTP responses by experimenting with identified HTTP Response vulnerabilities] The adversary sends maliciously crafted HTTP request to back-end HTTP infrastructure to inject adversary data into HTTP responses (intended for intermediary and/or front-end client/victim HTTP agents communicating with back-end HTTP infrastructure) for the purpose of interfering with the parsing of HTTP response. The intended consequences of the malicious HTTP request and the subsequent adversary injection and manipulation of HTTP responses will be observed to confirm applicability of identified vulnerabilities in the adversary's plan of attack. [Perform HTTP Response Smuggling attack] Using knowledge discovered in the experiment section above, smuggle a message to cause one of the consequences.	High
33	HTTP Request Smuggling Modification/manipulation of HTTP message headers, request-line and body parameters to disrupt and interfere in the interpretation and parsing of HTTP message lengths/boundaries for consecutive HTTP messages by HTTP agents in a HTTP chain or network path. [Survey network to identify target] The adversary performs network reconnaissance by monitoring relevant traffic to identify the network path and parsing of the HTTP messages with the goal of identifying potential targets. [Identify vulnerabilities in targeted HTTP infrastructure and technologies] The adversary sends a variety of benign/ambiguous HTTP requests to observe responses from HTTP infrastructure in order to identify differences/discrepancies in the interpretation and parsing of HTTP requests by examining supported HTTP protocol versions, message sizes, and HTTP headers. [Cause differential HTTP responses by experimenting with identified HTTP Request vulnerabilities] The adversary sends maliciously crafted HTTP requests to interfere with the parsing of intermediary and back-end HTTP infrastructure, followed by normal/benign HTTP request from the adversary or a random user. The intended consequences of the malicious HTTP requests will be observed in the HTTP infrastructure response to the normal/benign HTTP request to confirm applicability of identified vulnerabilities in the adversary's plan of attack. [Perform HTTP Request Smuggling attack] Using knowledge discovered in the experiment section above, smuggle a message to cause one of the consequences.	High

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