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CVE-2026-48710

Starlette has missing Host header validation that poisons request.url.path, bypassing path-based security checks

Medium6.5Known exploitedEPSS 70.3%
Published
Updated
Reserved
Assigned by
GitHub_M

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.

Exploited in the wild

CISA lists this vulnerability in its Known Exploited Vulnerabilities catalog as Kludex Starlette HTTP Request/Response Smuggling Vulnerability.

Added
2 Sept 2026
Fix due (US federal)
16 Sept 2026
Used by ransomware
Not known

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.

Scores

CVSS scores of CVE-2026-48710, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1Medium6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
redhat-SADPADP (enrichment)3.1Medium6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
NVDNVD · Analyzed3.1Medium6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS (exploitation in 30 days)
70.3% · top 0.6% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: active · Automatable: yes · Technical impact: partial
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.5.

Weakness

Affected products

Affected packages

From reviewed advisories of the GitHub Advisory Database.

References (28)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .