CVE-2026-48710VulnerabilityPublished 13 Aug 2026Updated 4 Nov 2026

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

Affects mcp-proxySource GCVE Database

Compare

Authoritative record:CVE-2026-48710· Medium 6.5

Exploited in the wild · KEV due 16 Sep 2026 · public detection template (Nuclei) : upgrade to 0.12.0_1 now.

Data as of 4 Nov 2026, 07:00 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

KEV deadline: 16 Sep 2026 US federal agencies must patch by this date; a sensible deadline for everyone else. Other KEV due dates
Patch: Available – fixed in 0.12.0_1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 26 May 2026
Detectable: evidence found.
nuclei template: Starlette - Improper Validation of Unsafe Equivalence in Input
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: evidence found.
Listed in CISA KEV 99 days after disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by GitHub, Inc.
22 May 202618:47 UTC, 4 days before disclosure
CVE published
on cve.org
26 May 202621:54 UTC, t = 0
In Threat Radar
record ingested
26 May 202622:18 UTC, 24 minutes after disclosure
Added to CISA KEV (opens in a new tab)
exploitation confirmed
2 Sep 2026, 99 days after disclosure
KEV remediation due
US federal deadline
16 Sep 2026, 113 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade mcp-proxy to 0.12.0_1.

Patches and advisories

Affected software

Product	Affected	Fixed in
Homebrewmcp-proxy`pkg:brew/mcp-proxy`Other threats	Affected >=0.8.2 <0.12.0_1	Fixed in 0.12.0_1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to Starlette version 0.12.0_1 or later, which includes validation of the Host header against RFC 9112 and RFC 3986 grammar and falls back to scope["server"] for malformed values. Alternatively, deploy an RFC-compliant reverse proxy (e.g., nginx, Apache, HAProxy, Caddy) in front of the ASGI server to reject malformed Host headers before they reach the application. Avoid relying on request.url.path for security-sensitive decisions; use the canonical ASGI scope path instead.

Description

A vulnerability in Starlette affects versions >=0.8.2 and <0.12.0_1 where the HTTP Host header is not properly validated before reconstructing request.url. This allows a malformed Host header to cause request.url.path to differ from the actual requested path, potentially bypassing path-based security checks that rely on request.url.path. The issue is mitigated if a fronting proxy rejects malformed Host headers or if the application does not rely on request.url.path for security decisions. A fixed version 0.12.0_1 is available.

Impact

The vulnerability can lead to bypass of path-based security restrictions if an application relies on request.url.path for authorization decisions. It does not directly grant unauthorized access or modify routing but can cause middleware or endpoints to misinterpret the requested path. The impact depends heavily on application design and use of request.url.path for security. Deployments behind proxies that normalize or reject malformed Host headers are less affected. The CVSS score is 6.5 (medium severity) reflecting limited confidentiality and integrity impact without direct availability impact.

Summary

Starlette versions >=0.8.2 and <0.12.0_1 do not validate the HTTP Host header before reconstructing request.url, violating RFC 9112 and RFC 3986 host grammar. Malformed Host headers containing characters like '/', '?', or '#' shift path/query boundaries during URL parsing, causing request.url.path to differ from the actual HTTP request path. This discrepancy can be exploited to bypass security middleware or endpoints that rely on request.url.path for access control, as routing uses the raw HTTP path. The vulnerability requires that the application uses request.url.path for security decisions rather than the canonical ASGI scope path. A patch in version 0.12.0_1 validates the Host header and falls back to scope["server"] for malformed values. Deployments behind RFC-compliant reverse proxies that reject malformed Host headers are mitigated.

References

Community reviews

Loading reviews…

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

Exploitation evidence

What to do

Patches and advisories

Affected software

Description

Impact

Summary

Nuclei detection templates

Proofs of concept on GitHub

References

Community reviews

Exploitation evidence

Timeline

What to do

Patches and advisories

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 07:00 UTC

Public exploits and detectiona Nuclei detection template, GitHub proofs of concept

Technical details

References

Community reviews

Related threats