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Dossier · Vulnerability

Actively exploited · CISA KEV · NVD published 2026-05-26

CVE-2026-48710

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.

Signals

Exploited in the wild
Yesadded 2026-09-02 · due 2026-09-16. An observation, not a forecast.
EPSS · 30-day forecast
7%Chance of exploitation in the next 30 days, 94th percentile of all CVEs. A forecast; KEV outranks it.
CVSS · NVD · MEDIUM
6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Internet exposure
not stated by sourcesNo exposure census on this CVE's dispatches.

Exploits

6 known · links only

GitHub PoCs · by trust, then stars5

  1. eris-ths/supply-chain-guard ↗Trust ok 100

    Detect, assess, and respond to supply chain attacks across npm/yarn and Python (pip/poetry/uv). Claude Code skill + standalone scripts. Built during axios RAT (2026-03-31) and Starlette BadHost CVE-2026-48710 (2026-05-22).

    ★ 3 · created 2026-04-01

  2. Bhanunamikaze/BadHost-CVE-2026-48710-Exploit ↗Trust ok 100

    Detection scanner for CVE-2026-48710 - Host-header auth bypass in Starlette/FastAPI

    ★ 1 · created 2026-05-28

  3. xtremebeing/starlette-host-header-lab ↗Trust ok 100

    Starlette Host-Header URL Confusion Lab (X41-2026-002) - CVE-2026-48710

    ★ 1 · created 2026-05-27

  4. CuteeCat/CVE-2026-48710 ↗Trust ok 100

    CVE-2026-48710漏洞验证代码

    ★ 0 · created 2026-08-11

  5. sb-ox/repro-OXDEV-77637-uv-workspace ↗Trust ok 100

    OXDEV-77637 repro fixture: uv workspace whose transitive CVE (starlette 0.25.0 / CVE-2026-48710) is dropped when the lean clone omits workspace-member pyproject.toml. Tag: repro-OXDEV-77637

    ★ 0 · created 2026-08-03

Fake proof-of-concept repositories have been used to deliver malware to the researchers who run them. The trust verdict is our engine's heuristic over the repository (account age, what it ships, how its stars arrived); it is a reason to read the code first, not a finding about its author.

Nuclei1

  1. Starlette - Improper Validation of Unsafe Equivalence in Input ↗

    A flaw was found in Starlette, a lightweight ASGI (Asynchronous Server Gateway Interface) framework. A remote attacker could exploit this vulnerability by sending a specially crafted HTTP Host request header. This malformed header could cause the request.url to be incorrectly reconstructed, leading to a discrepancy with the actual requested path. Consequently, security restrictions enforced by middleware and endpoints that rely on request.url for validation could be bypassed, potentially allowin

    yaml · seen 2026-10-18

On the wire

1 dispatch
  1. [KEV] CVE-2026-48710: Kludex Starlette HTTP Request/Response Smuggling VulnerabilityKEV

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