Which versions of Microsoft are affected by CVE-2026-39912?

V2Board and Xboard installations are vulnerable to unauthenticated account takeover affecting all user accounts including administrators through a compromised email-based authentication mechanism.. A patch is available.

Is there a public PoC exploit available for CVE-2026-39912?

Yes, a public proof-of-concept exploit is available for CVE-2026-39912. Prioritise patching immediately. EPSS: 0.1%.

How to fix or mitigate CVE-2026-39912?

Within 24 hours: Identify all V2Board and Xboard instances in production and verify affected versions. Within 7 days: Apply vendor-released patch to V2Board ≥1.7.5 and Xboard ≥0.2.0, or immediately disable the login_with_mail_link_enable feature if patching cannot be completed. Within 30 days: Conduct account audit for unauthorized access, reset all admin credentials, review authentication logs for exploitation attempts, and implement network-level controls restricting loginWithMailLink endpoint access to authorized users only.

Microsoft CVE-2026-39912

Q: What is the CVSS score of CVE-2026-39912?

CVE-2026-39912 has a CVSS 4.0 base score of 9.1 (Critical). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.1%.

EUVD-2026-21043 CRITICAL

Insertion of Sensitive Information Into Sent Data (CWE-201)

2026-04-09 VulnCheck

GHSA-83h9-46h8-whf4

Information Disclosure Microsoft

9.1

CVSS 4.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

PoC Detected

Apr 09, 2026 - 19:16 vuln.today

Public exploit code

EUVD ID Assigned

Apr 09, 2026 - 19:15 euvd

EUVD-2026-21043

Analysis Generated

Apr 09, 2026 - 19:15 vuln.today

Patch released

Apr 09, 2026 - 19:15 nvd

Patch available

CVE Published

Apr 09, 2026 - 18:35 nvd

CRITICAL 9.1

DescriptionNVD

V2Board 1.6.1 through 1.7.4 and Xboard through 0.1.9 expose authentication tokens in HTTP response bodies of the loginWithMailLink endpoint when the login_with_mail_link_enable feature is active. Unauthenticated attackers can POST to the loginWithMailLink endpoint with a known email address to receive the full authentication URL in the response, then exchange the token at the token2Login endpoint to obtain a valid bearer token with complete account access including admin privileges.

AnalysisAI

Authentication bypass in V2Board 1.6.1-1.7.4 and Xboard ≤0.1.9 enables unauthenticated account takeover including admin privileges. When login_with_mail_link_enable is active, attackers POST known email addresses to the loginWithMailLink endpoint, receiving full authentication URLs in HTTP responses. …

RemediationAI

Within 24 hours: Identify all V2Board and Xboard instances in production and verify affected versions. Within 7 days: Apply vendor-released patch to V2Board ≥1.7.5 and Xboard ≥0.2.0, or immediately disable the login_with_mail_link_enable feature if patching cannot be completed. …

Analysis

Detailed AI-generated intelligence summary covering attack vector, impact assessment, affected versions, remediation steps, and indicators of compromise.

POChttps://••••••••••.com/exploit

PATCHhttps://••••••••••.com/patch

ADVISORYhttps://••••••••••.com/advisory