CVE-2026-48710: Kludex Starlette HTTP Request/Response Smuggling Vulnerability
What it 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.
What to do
Schedule the vendor fix into this week’s change window, prioritising internet-facing and business-critical systems. Confirm the fix is applied everywhere, not just where it was easy.
- Priority
- This week: Schedule into this week’s change window.
- Severity (CVSS)
- 6.5 medium
- CISA assessment (SSVC)
- actively exploited; attackers can automate it at scale; partial control or data exposure
- Exploit probability (EPSS, 30 days)
- 7.1%, higher than 94% of all CVEs
- Added to CISA KEV
- 2 September 2026
- CISA fix-by date
- 16 September 2026 (US federal agencies; a sensible deadline for everyone)
- Ransomware use
- Not known
- Weakness
- CWE-444, CWE-1289
References
- NIST NVD entry
- CISA KEV entry
- badhost.org
- github.com/Kludex/starlette/commit/764dab0dcfb9033d75442d7a359645c9f94648c6
- github.com/Kludex/starlette/security/advisories/GHSA-86qp-5c8j-p5mr
- github.com/pypa/advisory-database/tree/main/vulns/starlette/PYSEC-2026-161.yaml
- ostif.org/disclosing-the-badhost-vulnerability-in-starlette
- www.secwest.net/starlette
Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.