CVE-2026-116685VulnerabilityPublished 29 Oct 2026

mcp-atlassian · Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and

Affects mcp-atlassianSource GCVE Database

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Authoritative record:CVE-2026-116685· Medium 5.9

Not known to be exploited · CVSS 5.9 Medium : upgrade to 0.23.1_1 when convenient.

Data as of 30 Oct 2026, 08:32 UTC

CVSS 3.1 base score

5.9Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	5.9

Patch: Available – fixed in 0.23.1_1

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (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 0.23.1_1.

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.9 <0.23.1_1	Fixed in 0.23.1_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 MCP Python SDK version 1.30.0 (1.x) or 2.2.0 (2.x) or later, which restrict redirect following to the same origin or scheme upgrades and cause other redirects to fail. No code changes are required. Until upgrade, supply your own HTTP client with follow_redirects set to False to prevent automatic cross-origin redirects. If a client may have followed a redirect to an untrusted host, rotate any credentials that were sent. Avoid relying on redirects to different hosts; instead, set the endpoint URL directly to the final target. The vendor provides an unsupported workaround to forcibly follow redirects if absolutely necessary, but this is not recommended due to security risks.

Description

The Model Context Protocol (MCP) Python SDK versions 1.8.0 through 1.29.1 and 2.0.0 through 2.1.1 improperly followed HTTP redirects across origins while carrying custom headers and, on certain redirects, the request body. This behavior could expose sensitive headers such as API keys to unintended hosts if the trusted endpoint redirects to a different origin. The SDK's OAuth client providers were similarly affected. The issue is fixed in MCP versions 1.30.0 and 2.2.0, which restrict redirects to the same origin or scheme upgrades on the same host. No code changes are needed to apply the fix.

Impact

Sensitive custom headers such as API keys and request bodies could be leaked to unintended hosts if a trusted MCP endpoint redirects to a different origin. This could allow an attacker who controls or influences the redirect target to capture these credentials. The Authorization bearer token is not exposed on cross-origin redirects. The vulnerability does not affect MCP servers or clients that do not follow redirects. The impact is limited to confidentiality of custom headers and request bodies during cross-origin redirects.

Summary

In affected MCP Python SDK versions, the Streamable HTTP and SSE client transports followed HTTP redirects to any host, forwarding custom headers (e.g., X-API-Key) and, on 307 or 308 redirects, the request body. OAuth client providers also followed redirects similarly. The lone Authorization bearer header was not forwarded on cross-origin redirects due to HTTP library behavior. An attacker able to cause a trusted MCP endpoint to redirect to a different origin could capture these headers and request bodies. The vulnerability affects SDK clients using HTTP transports with follow_redirects enabled. The issue is resolved in MCP 1.30.0 and 2.2.0 by restricting redirects to the same origin or scheme upgrades, causing other redirects to fail with an error. Until upgrade, users can mitigate by disabling follow_redirects on their HTTP clients or rotating credentials if a redirect to an untrusted host occurred.

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:32 UTC

Technical details

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