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Advisory record · GHSA-86qp-5c8j-p5mr

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

CVSS 6.5 MediumCriticalIn CISA KEVEPSS 0.70 · 99th percentile

Critical, because:

  • In CISA’s KEV catalogue since 2 Sept 2026: it is known to be exploited.

How we decide what’s critical

Published by the GitHub Advisory Database at 4 Jun 2026, 13:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
starlettePyPI<1.0.11.0.1
Identifiers
GHSA-86qp-5c8j-p5mr · CVE-2026-48710 · PYSEC-2026-161 · X41-2026-002
Weakness (CWE)
CWE-444 · CWE-1289
Tags
Published
4 Jun 2026
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Starlette versions before 1.0.1 do not validate the HTTP Host header before rebuilding request.url, so a malformed Host value can make request.url.path differ from the path actually routed. An attacker who can send requests to the application can bypass middleware or endpoint checks that rely on request.url.path, such as path-prefix authorization. Upgrade to Starlette 1.0.1 or later. The source gives no other workaround.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.5 Medium 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N CNA (GitHub_M)
  • CISA KEV Listed since 2 Sept 2026: known to be exploited.
  • EPSS 0.70, the 99th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:11 UTC First seen by agentprime
  2. 31 Oct 2026, 14:11 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.