What is the CVSS score of CVE-2026-33427?

CVE-2026-33427 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. EPSS exploitation probability: 0.1%.

Which versions of Discourse are affected by CVE-2026-33427?

Organizations using Discourse face notable risk from CVE-2026-33427, a missing authorization vulnerability rated CVSS 7.5.

How to fix or mitigate CVE-2026-33427?

Within 7 days: Identify all affected systems and apply vendor patches promptly. Monitor vendor channels for patch availability.

Discourse CVE-2026-33427

HIGH

Missing Authorization (CWE-862)

2026-03-20 GitHub_M

Authentication Bypass Discourse

7.5

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

7.5 HIGH

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

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Mar 20, 2026 - 23:46 vuln.today

CVE Published

Mar 20, 2026 - 23:20 nvd

HIGH 7.5

DescriptionGitHub Advisory

Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, an unauthenticated attacker can cause a legitimate Discourse authorization page to display an attacker-controlled domain, facilitating social engineering attacks against users. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. No known workarounds are available.

AnalysisAI

Discourse versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain an authorization page spoofing vulnerability that allows unauthenticated attackers to inject attacker-controlled domains into legitimate Discourse authorization pages, enabling social engineering attacks. This CWE-862 (Missing Authorization) class vulnerability affects all affected Discourse installations and requires no authentication or special privileges to exploit. No active exploitation in the wild (KEV status) has been reported, but the attack surface is broad given Discourse's widespread use as an open-source discussion platform.

Technical ContextAI

The vulnerability stems from inadequate input validation or output encoding in Discourse's authorization flow implementation, classified as CWE-862 (Missing Authorization). Specifically, the authorization page fails to properly validate or sanitize domain references, permitting an unauthenticated attacker to control which domain is displayed to users during the authorization process. This is a client-side trust violation rather than a cryptographic bypass; the underlying OAuth or SSO mechanism remains intact, but the presentation layer is compromised. The affected product is Discourse (cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*), an open-source Perl/Ruby-based discussion platform widely deployed in enterprise and community settings. The flaw likely resides in template rendering, URL parameter handling, or redirect validation within the authentication controller.

RemediationAI

Immediately upgrade Discourse to version 2026.3.0-latest.1, 2026.2.1, or 2026.1.2 depending on your current release branch; see https://github.com/discourse/discourse/security/advisories/GHSA-9vhg-2mx3-mqfr for patch details and upgrade procedures. Until patching is completed, implement Content Security Policy (CSP) headers with strict frame-ancestors and default-src directives to prevent authorization page injection, enforce HTTPS with HSTS across all authentication endpoints, and educate users to verify domain ownership in the browser address bar before entering credentials on Discourse login pages. No official workarounds are available; patching is the only remediation path.