Known exploited vulnerability · CISA KEV

CVE-2026-48710: 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.

CVE-2026-48710

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-09-02: attackers are using it right now.

CISA KEV: Listed; Added 2026-09-02 · federal fix-by 2026-09-16
EPSS (30 days): 70%; Higher than 99.4% of CVEs · 2026-11-01
CVSS: No score

What CISA says

Kludex Starlette HTTP Request/Response Smuggling Vulnerability

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.

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How to check if you are exposed to CVE-2026-48710

Find every Kludex Starlette system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2026-48710.

US federal agencies had to fix this by 2026-09-16. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Timeline

2026-09-02 · Added to CISA's Known Exploited Vulnerabilities catalog
2026-09-16 · Fix-by date for US federal agencies, passed 46 days ago

Vendor advisories and fixes

https://github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr

Weakness type

CWE-444

Keep going

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.