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PYSEC-2026-388

CriticalCVSS 9.5 / 10
Published Jun 29, 2026·Last modified Jun 29, 2026
Affected Components(0)

No affected components available

Description

Impact

A Host-header parsing flaw in the LiteLLM proxy could, under specific conditions, allow unauthenticated access to protected management routes.

The auth layer derived the effective route from request.url.path in litellm/proxy/auth/auth_utils.py::get_request_route(), which Starlette reconstructs from the Host header. A crafted Host could therefore make the auth gate evaluate a different route from the one FastAPI dispatched.

Most deployments are not affected. The bypass is blocked by any upstream layer that validates or normalizes Host, such as:

  • a CDN or WAF, such as Cloudflare
  • a reverse proxy with server_name allowlists
  • a host-based load balancer

LiteLLM Cloud customers are not affected.

Patches

Fixed in 1.84.0. Upgrade to 1.84.0 or later. No configuration change is required.

Workarounds

If upgrading is not immediately possible, place the proxy behind an upstream component that validates or normalizes the Host header before forwarding (a CDN/WAF, a reverse proxy with explicit server_name allowlists, or a cloud load balancer with host-based routing rules), or otherwise restrict network access to the proxy listener.

References

Discovery Credit: Le The Thang (KCSC) and Kim Ngoc Chung (One Mount Group)

Risk Scores
Base Score
9.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
8.4

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.59%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Critical severity
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