VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-44681: Mcp atlassian · Authlib OIDC Implicit/Hybrid Authorization Vulnerable to Open Redirect

Affects mcp-atlassianSource GCVE Database

Compare

Not known to be exploited · CVSS 6.1 Medium : upgrade to 0.21.1_4 when convenient.

Data as of 30 Oct 2026, 08:31 UTC

CVSS 3.1 base score

6.1Medium

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

Patch: Available – fixed in 0.21.1_4

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Changed
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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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

Disclosed: evidence found.
CVE published 13 Aug 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 0.21.1_4.

Affected software

Product	Affected	Fixed in
Homebrewmcp-atlassian`pkg:brew/mcp-atlassian`Other threats	Affected >=0.11.11 <0.21.1_4	Fixed in 0.21.1_4

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

AI-suggested

A patch is available in Authlib version 0.21.1_4 that fixes this open redirect vulnerability. Users should upgrade to version 0.21.1_4 or later. Until patched, avoid enabling the OpenIDImplicitGrant or OpenIDHybridGrant flows if possible. No other mitigations are indicated by the vendor advisory.

Description

Authlib's OpenID Connect Implicit and Hybrid authorization endpoints contain an unauthenticated open redirect vulnerability. An attacker can craft an authorization request omitting the 'openid' scope, causing the server to redirect users to an attacker-controlled URL. This occurs because the scope validation error redirects using an unvalidated redirect_uri parameter. The flaw affects Authlib versions from 0.11.11 up to but not including 0.21.1_4 and has been fixed in 0.21.1_4. The vulnerability enables phishing and credential harvesting by leveraging the trusted authorization server's domain in the redirect.

Impact

This vulnerability allows an attacker to cause the authorization server to redirect users to a malicious site under the attacker's control. Because the redirect originates from the legitimate authorization server domain, it can be used to facilitate phishing attacks and credential harvesting by exploiting user trust and domain allow-listing. The vulnerability does not leak tokens or authorization codes directly, as it triggers before authorization decisions. However, it violates OAuth 2.0 security requirements and can contribute to account takeover when combined with other issues. The CVSS score is 6.1 (medium severity).

Summary

The vulnerability exists in Authlib's OpenIDImplicitGrant and OpenIDHybridGrant classes, where the presence of the 'openid' scope is checked before validating the redirect_uri against the client's registered URIs. When the 'openid' scope is missing, an InvalidScopeError is raised with the raw redirect_uri from the request, which is attacker-controlled and unvalidated. The OAuth2Error handler then issues an HTTP 302 redirect to this unvalidated URI, enabling an open redirect. This flaw violates OAuth 2.0 and OpenID Connect security best practices that mandate redirect_uri validation even in error responses. The issue affects any Authlib-based OpenID Connect provider supporting the Implicit or Hybrid flow with vulnerable versions. No authentication or valid client_id is required to trigger the redirect.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 08:31 UTC

Technical details

References

Community reviews

Related threats