CVE-2026-48710VulnerabilityPublished 13 Aug 2026Updated 31 Oct 2026

Snyk agent scan: Starlette has missing Host header validation that poisons request.url.path, bypassing path-based

Affects Kludex snyk-agent-scanSource 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) : upgrade to 0.5.4_1 now.

Data as of 1 Nov 2026, 01:51 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 0.5.4_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 31 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 snyk-agent-scan to 0.5.4_1.

Patches and advisories

Affected software

Product	Affected	Fixed in
Homebrewsnyk-agent-scan`pkg:brew/snyk-agent-scan`Other threats	Affected >=0.4.3 <0.5.4_1	Fixed in 0.5.4_1

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

Starlette versions from 0.4.3 up to but not including 0.5.4_1 have a vulnerability where the HTTP Host header is not validated before reconstructing request.url. This allows an attacker to craft a malformed Host header that causes 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 fixed in version 0.5.4_1 by validating the Host header against RFC 9112 and RFC 3986 grammar and falling back to a safe value if malformed.

Impact

Applications using affected Starlette versions that rely on request.url or request.url.path for security-sensitive decisions, such as path-based access control, are vulnerable to bypass. Attackers can craft Host headers that cause request.url.path to differ from the actual requested path, allowing unauthorized access to protected paths. Deployments behind proxies are only protected if those proxies properly validate or normalize Host headers. There is no indication of active exploitation in the wild. The CVSS 3.1 score is 6.5 (medium severity) reflecting network attack vector, low complexity, no privileges required, no user interaction, and limited confidentiality and integrity impact.

Mitigation

A patch is available and should be applied by upgrading to Starlette version 0.5.4_1 or later, which validates the Host header against RFC 9112 and RFC 3986 grammar and falls back to a safe server value if malformed. If upgrading is not immediately possible, ensure that any fronting proxies or load balancers reject or normalize malformed Host headers to prevent this attack vector. Avoid relying on request.url.path for security decisions without proper validation of the Host header.

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

Community reviews

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Snyk agent scan: Starlette has missing Host header validation that poisons request.url.path, bypassing path-based

Exploitation evidence

What to do

Patches and advisories

Affected software

Description

Impact

Mitigation

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 1 Nov 2026, 01:51 UTC

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

WeaknessesCWE-444

Technical details

References

Community reviews

Related threats