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

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

Affects mcp-atlassianSource 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 0.21.1_7 now.

Data as of 30 Oct 2026, 08:16 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 0.21.1_7

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 mcp-atlassian to 0.21.1_7.

Patches and advisories

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.9 <0.21.1_7	Fixed in 0.21.1_7

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 0.21.1_7 or later, which includes proper Host header validation. 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 decisions; use the canonical ASGI scope path instead.

Description

A vulnerability in Starlette allows an attacker to send a malformed HTTP Host header that causes the reconstructed request.url.path to differ from the actual requested path. This discrepancy can bypass security checks in middleware or endpoints that rely on request.url.path for access control. The issue affects versions from 0.11.9 up to but not including 0.21.1_7. The vulnerability does not directly grant unauthorized access but can lead to path-based authorization bypass if the application depends on request.url.path instead of the canonical ASGI path. Mitigation involves upgrading to a fixed version or using an RFC-compliant reverse proxy to reject malformed Host headers.

Impact

The vulnerability allows attackers to craft Host headers that cause request.url.path to differ from the actual request path, enabling bypass of path-based authorization checks if the application relies on request.url.path for security decisions. It does not directly grant access or modify routing. The impact depends on application design and is rated moderate to low in many real-world deployments where path-based authorization is not used or proxies sanitize Host headers.

Summary

In affected Starlette versions, the HTTP Host header was not validated before reconstructing request.url, allowing malformed Host headers containing characters like '/', '?', or '#' to alter the parsed request.url.path. This causes a mismatch between the routing path and the path used by middleware or endpoints for security decisions, potentially bypassing path-based access controls. The vulnerability impacts applications relying on request.url.path for security rather than the canonical ASGI scope path. The issue is fixed in version 0.21.1_7, which validates the Host header per RFC 9112 and RFC 3986 and falls back to scope["server"] for malformed values. Deployments behind proxies that normalize or reject malformed Host headers are less impacted.

References

Community reviews

Loading reviews…

Mcp atlassian: 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

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, 08:16 UTC

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

Technical details

References

Community reviews

Related threats