CVE-2026-48710

Kludex Starlette: HTTP Request/Response Smuggling

As of , CVE-2026-48710 in Kludex Starlette is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch soon.

Exploited
Yes: CISA listed it on 2 September 2026
US federal deadline
16 September 202614 days after CISA listed it. US federal civilian agencies must fix it by then.
Used in ransomware campaigns
Not known to CISA
EPSS score
0.07Higher than 94% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
Public exploit
None foundNeither Metasploit nor Exploit-DB lists one.
Fix
Vendor advice: github.comLinks below, from CISA's entry.

What CISA says to do

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.

CISA's required action

  • github.comThis vulnerability affects an open-source component, third-party library, protocol, or proprietary implementation that could be used by…

What the flaw is

Kludex Starlette contains a HTTP request/response smuggling vulnerability that could allow attackers to inject paths into the host part, prepending the actual path leading to issues such as authentication bypass when the authentication depends on the reconstructed URL’s path. This vulnerability could be chaned with CVE-2026-42271.

CISA's 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.

The CVE record's description, from GitHub_M

CVE published
26 May 2026
Assigned by
GitHub_M
CVSS
6.5 Medium (CVSS 3.1, from the CNA)
CWE-444
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CISA SSVC, exploitation
active
CISA SSVC, automatable
yes
CISA SSVC, technical impact
partial

Timeline

  1. The CVE record was published.
  2. CISA added it to its list of exploited vulnerabilities.
  3. The US federal deadline to fix it.

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