CVE-2026-48710
Kludex Starlette HTTP Request/Response Smuggling Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 16 September 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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 3.1
- 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
- EPSS
- 36.26% probability · 98th percentile
- CISA KEV
- Listed 2 September 2026 · due 16 September 2026
- Weakness
- CWE-444, CWE-1289
- Affected
- encode/starlette · redhat/ai inference server · redhat/ansible automation platform · redhat/migration toolkit for applications · redhat/openshift ai · redhat/openshift lightspeed · redhat/satellite · redhat/enterprise linux ai
- Source
- security-advisories@github.com
CISA notes
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. This vulnerability affects an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see: https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-48710
References
- https://badhost.orgMitigation, Third Party Advisory
- https://github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6Patch
- https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mrVendor Advisory
- https://github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yamlThird Party Advisory
- https://ostif.org/disclosing-the-badhost-vulnerability-in-starletteMitigation, Third Party Advisory
- https://www.secwest.net/starletteExploit, Mitigation, Third Party Advisory
- https://www.x41-dsec.de/lab/advisories/x41-2026-002-starletteExploit, Mitigation, Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:22992Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:22993Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:23346Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:24866Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:26226Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:30088Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:30089Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:34456Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:34526Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:34532Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:37275Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:43038Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:44696Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:51357Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:60520Third Party Advisory
- https://access.redhat.com/errata/RHSA-2026:63337Third Party Advisory
- https://access.redhat.com/security/cve/CVE-2026-48710Third Party Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2481742Issue Tracking, Third Party Advisory
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48710.jsonThird Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-48710Third Party Advisory, US Government Resource
- https://www.wiz.io/blog/ai-infrastructure-honeypotExploit, Third Party Advisory
- https:/www.microsoft.com/en-us/security/blog/2026/08/26/when-ai-infrastructure-becomes-target-securing-gateways-control-pointsBroken Link
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.