CVE-2026-48746Public exploitNetwork attack vectorHinoki check available

Unauthenticated API access via malformed Host header

Published Jun 22, 2026 · Updated Jun 22, 2026

Authentication bypass in vLLM allows remote attackers to access protected OpenAI API endpoints through a malformed Host header. AuthenticationMiddleware checks a URL path reconstructed by Starlette from the unvalidated Host header, while FastAPI routes on the actual request path. The flaw affects 0.3.0 and later releases before 0.22.0 when API-key authentication is enabled, the API is attacker-reachable, and no RFC-conforming reverse proxy rejects the header.

CVSS severity9.1
Critical
EPSS probability1.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Authentication bypass in vLLM allows remote attackers to access protected OpenAI API endpoints through a malformed Host header. AuthenticationMiddleware checks a URL path reconstructed by Starlette from the unvalidated Host header, while FastAPI routes on the actual request path. The flaw affects 0.3.0 and later releases before 0.22.0 when API-key authentication is enabled, the API is attacker-reachable, and no RFC-conforming reverse proxy rejects the header.

The record

CVE
CVE-2026-48746
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
vLLM Project
Product
vLLM
Classifications
CWE-444, CWE-501, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.3.0, < 0.22.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

vLLM Project · vLLMversion=>= 0.3.0, < 0.22.0

Published CVSS scores

9.1Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
9.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CWE-501Trust Boundary Violation
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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