What is the CVSS score of CVE-2026-42849?

CVE-2026-42849 has a CVSS 3.1 base score of 9.3 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N. EPSS exploitation probability: 0.0%.

Which versions of authentik are affected by CVE-2026-42849?

authentik identity provider contains a critical cross-site scripting vulnerability in its authentication flow that enables session hijacking and compromise of identity systems.. A patch is available.

How to fix or mitigate CVE-2026-42849?

Within 24 hours: Identify all authentik deployments and confirm which are running versions prior to 2025.12.5 (2025.x series) or 2026.2.3 (2026.x series). Within 7 days: Develop and test upgrade plan to patched versions. Within 30 days: Execute patch deployment to authentik 2025.12.5 or 2026.2.3 or later across all instances.

authentik CVE-2026-42849

EUVD-2026-34026 CRITICAL

Cross-site Scripting (XSS) (CWE-79)

2026-06-02 GitHub_M

XSS Authentik

9.3

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

9.3 CRITICAL

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

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

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Patch available

Jun 02, 2026 - 22:01 EUVD

Analysis Generated

Jun 02, 2026 - 21:21 vuln.today

DescriptionGitHub Advisory

authentik is an open-source identity provider. Prior to versions 2025.12.5 and 2026.2.3, due to the implementation of stages in the SFE (Simple Flow Executor) in order to make the interface more compatible with legacy browsers, it was possible to use an XSS exploit in the AutosubmitStage. This issue has been patched in versions 2025.12.5 and 2026.2.3.

AnalysisAI

Cross-site scripting in authentik identity provider versions prior to 2025.12.5 and 2026.2.3 allows remote attackers to execute arbitrary JavaScript in a victim's browser by abusing the AutosubmitStage within the Simple Flow Executor (SFE). With a CVSS of 9.3 reflecting scope change and high impact to confidentiality/integrity, exploitation enables session hijacking against an identity provider, but no public exploit identified at time of analysis.

Technical ContextAI

authentik is an open-source identity and access management (IdP) platform developed by goauthentik, used as an SSO/federation broker (SAML, OIDC, LDAP). The vulnerability resides in the Simple Flow Executor (SFE), a fallback flow-rendering interface designed for legacy browsers that cannot run the modern Web Component-based UI. Specifically, the AutosubmitStage - a stage that auto-submits HTML form data (typically for SAML POST bindings or external redirects) - failed to properly encode/escape user-controllable values before injecting them into the rendered HTML, matching CWE-79 (Improper Neutralization of Input During Web Page Generation). Because the SFE renders inside the IdP's trusted origin during authentication flows, script execution occurs in a security-sensitive context.

RemediationAI

Vendor-released patch: upgrade authentik to 2025.12.5 (for the 2025.12.x branch) or 2026.2.3 (for the 2026.2.x branch) as documented in advisory GHSA-pgff-5mx8-fqj3 at https://github.com/goauthentik/authentik/security/advisories/GHSA-pgff-5mx8-fqj3. If immediate patching is not possible, disable the Simple Flow Executor fallback so flows render only via the modern Web Component UI - note this will break authentication for genuinely legacy browsers (IE-era / non-ES6 clients) and any embedded WebViews that rely on the SFE path. As additional compensating controls, enforce a strict Content-Security-Policy on the authentik web frontend (script-src 'self' without 'unsafe-inline') which can blunt arbitrary script execution at the cost of breaking custom branding/scripts, and restrict admin-interface network exposure via IP allowlisting on the reverse proxy so a phished admin session cannot be reached externally.