CVE-2026-48710VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

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

Affects Kludex mcpmSource GCVE Database

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Authoritative record:CVE-2026-48710· Medium 6.5

Exploited in the wild · KEV due 16 Sep 2026 · public detection template (Nuclei) · 70% EPSS : upgrade to 2.15.0 now.

Data as of 30 Oct 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
EPSS: 70.2% chance of exploitation in 30 days – higher than 99% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.15.0

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 29 Oct 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 Kludex mcpm to 2.15.0.

Patches and advisories

Affected software

Product	Affected	Fixed in
Homebrewmcpm`pkg:brew/mcpm`Other threats	Affected >=1.0.3 <2.15.0	Fixed in 2.15.0

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

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Description

A vulnerability in Starlette versions >=1.0.3 and <2.15.0 allows an attacker to bypass path-based security checks by sending a malformed HTTP Host header. This causes the reconstructed request.url.path to differ from the actual requested path, potentially bypassing middleware or endpoint security that relies on request.url.path. The vulnerability is mitigated by validating the Host header against RFC 9112 and RFC 3986 grammar or by using a reverse proxy that rejects malformed Host headers.

Impact

The vulnerability can lead to bypass of path-based authorization or authentication controls if the application relies on request.url.path for security decisions. It does not directly grant access or modify routing but can cause security checks to be circumvented. Deployments behind reverse proxies that reject or normalize malformed Host headers are mitigated. The overall impact is rated medium with a CVSS score of 6.5. Known exploits exist in the wild. The severity depends heavily on downstream application design rather than the framework alone.

Mitigation

Upgrade to Starlette version 2.15.0 or later, which validates the Host header according to RFC 9112 and RFC 3986 and falls back to the server scope 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. Review and update any custom middleware to avoid relying on request.url.path for security decisions and instead use the canonical ASGI path.

Summary

Starlette, a lightweight ASGI framework, improperly validates the HTTP Host header before reconstructing request.url. The routing algorithm uses the raw HTTP path, but request.url is rebuilt from the Host header concatenated with the path. If the Host header contains invalid characters such as '/' or '?', the reconstructed request.url.path can differ from the actual request path. This discrepancy allows middleware or endpoints that rely on request.url.path for security decisions to be bypassed. The vulnerability affects versions >=1.0.3 and <2.15.0 and was fixed in version 2.15.0. Exploitation requires sending a specially crafted Host header. The impact depends on application design, specifically if security checks rely on request.url.path rather than the canonical ASGI path.

CWE-444Inconsistent Interpretation of HTTP Requests (HTTP Request Smuggling) (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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

Exploitation evidence

What to do

Patches and advisories

Affected software

Description

Impact

Mitigation

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 30 Oct 2026, 07:00 UTC

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

WeaknessesCWE-444

Technical details

References

Community reviews

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