CVE-2026-48710

Kludex Starlette

score 75Known exploited · added 2026-09-02Public PoC ×5Nuclei template

Summary

Kludex Starlette HTTP Request/Response Smuggling Vulnerability

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.

Published 2026-09-02 · first seen here 2026-10-10

CISA required action (due 2026-09-16): 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.

Analysis & write-ups

No technical write-up from a research team yet. Contact Zero checks Unit 42, Google/Mandiant, Microsoft, Talos, CrowdStrike, Rapid7, watchTowr and others several times a day, plus NVD and CISA reference links.

Exploit availability

Public exploit code lowers the bar for attackers, so prioritise patching and hunting. These repositories are unverified. Fake PoCs that contain malware are common, so never run them outside an isolated lab.

Nuclei detection template · ProjectDiscovery
eris-ths/supply-chain-guard · ★3 · created 2026-04-01
xtremebeing/starlette-host-header-lab · ★1 · created 2026-05-27
Bhanunamikaze/BadHost-CVE-2026-48710-Exploit · ★1 · created 2026-05-28
sb-ox/repro-OXDEV-77637-uv-workspace · ★0 · created 2026-08-03
CuteeCat/CVE-2026-48710 · ★0 · created 2026-08-11

Where it shows in your logs

Server or web application · HTTP request smuggling medium confidence

What to look for

Requests with both Content-Length and Transfer-Encoding headers, or malformed chunked encoding
Responses or sessions crossing between users: one user's session suddenly used from another IP
Requests to admin paths that the front-end proxy should have blocked
The application's process (w3wp.exe, java, tomcat, node, php-fpm, httpd, python) starting shells or LOLBins (cmd, powershell, sh, bash, curl, wget, certutil)
New script files in web roots (.jsp, .aspx, .php): a web shell
Requests to unusual URLs on the application from internet IPs right before any of the above
Outbound connections from the server to new external IPs

Data sources

Web server and WAF logs · ATT&CK DS0015 Application Log Content

Sentinel: W3CIISLogAppServiceHTTPLogsAzureDiagnostics (Application Gateway / Front Door WAF)_Im_WebSession
Splunk: Web.Webms:iis:autoaccess_combinedWAF / proxy sourcetypes
CrowdStrike: Falcon Next-Gen SIEM: third-party web / WAF / proxy logs

Process creation · ATT&CK DS0009 Process Creation

Sentinel: DeviceProcessEventsSecurityEvent (4688)Sysmon Event ID 1_Im_ProcessCreate
Splunk: Endpoint.ProcessesXmlWinEventLog:Microsoft-Windows-Sysmon/OperationalWinEventLog:Security (4688)
CrowdStrike: ProcessRollup2SyntheticProcessRollup2

File creation · ATT&CK DS0022 File Creation

Sentinel: DeviceFileEventsSysmon Event ID 11_Im_FileEvent
Splunk: Endpoint.FilesystemSysmon Event ID 11
CrowdStrike: NewExecutableWrittenNewScriptWritten*FileWritten events

Network connections · ATT&CK DS0029 Network Connection Creation / Network Traffic Flow

Sentinel: DeviceNetworkEventsCommonSecurityLog (firewall)_Im_NetworkSession
Splunk: Network_Traffic.All_TrafficFirewall sourcetypes (pan:traffic, fortigate_traffic, cisco:asa)
CrowdStrike: NetworkConnectIP4NetworkReceiveAcceptIP4NetworkConnectIP6

Authentication and sessions · ATT&CK DS0028 Logon Session Creation / DS0002 User Account Authentication

Sentinel: SigninLogsSecurityEvent (4624, 4625, 4648)DeviceLogonEventsIdentityLogonEvents_Im_Authentication
Splunk: Authentication.Authenticationpan:globalprotectVPN sourcetypes
CrowdStrike: UserLogonUserLogonFailed2Falcon Identity Protection events

A generic baseline worked out from the product type and weakness (CWE-444), not a detection. Check table and field names against your environment. Hunt queries for Sigma, Splunk, Sentinel and CrowdStrike are coming.