Vaultwarden CVE-2026-43914: Brute-Force Bypass via 2FA Email
The National Vulnerability Database has disclosed CVE-2026-43914, a critical flaw in Vaultwarden, the popular Rust-based Bitwarden-compatible server. Prior to version 1.35.4, Vaultwarden’s login brute-force protection can be entirely bypassed when email-based two-factor authentication (2FA) is enabled.
The vulnerability stems from the /api/two-factor/send-email-login endpoint, which, according to the National Vulnerability Database, acts as an oracle. It confirms whether a username-password combination is correct without rate-limiting, even if the user does not have email 2FA configured. An attacker can repeatedly query this endpoint to brute-force passwords unimpeded, significantly increasing the success rate of credential compromise.
This is a high-severity issue (CVSS 7.3) that directly impacts the integrity of user accounts. The fix is available in Vaultwarden version 1.35.4. Defenders running older versions need to prioritize this update immediately to mitigate the risk of account takeover.
What This Means For You
- If your organization relies on Vaultwarden for password management, you are exposed to unconstrained brute-force attacks. Immediately upgrade to version 1.35.4 or later. Audit logs for repeated failed login attempts against the `/api/two-factor/send-email-login` endpoint, even if you don't use email 2FA.
Related ATT&CK Techniques
🛡️ Detection Rules
3 rules · 6 SIEM formats3 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Vaultwarden CVE-2026-43914: Brute-Force Bypass via 2FA Email Endpoint
title: Vaultwarden CVE-2026-43914: Brute-Force Bypass via 2FA Email Endpoint
id: scw-2026-05-11-ai-1
status: experimental
level: high
description: |
Detects the abuse of the /api/two-factor/send-email-login endpoint in Vaultwarden versions prior to 1.35.4. This endpoint, when email 2FA is enabled, acts as an oracle for validating username-password combinations, allowing attackers to bypass brute-force protection and brute-force passwords without rate-limiting. This rule specifically targets the vulnerable API path used in the exploit.
author: SCW Feed Engine (AI-generated)
date: 2026-05-11
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-43914/
tags:
- attack.credential_access
- attack.t1110.004
logsource:
category: webserver
detection:
selection:
cs-uri|contains:
- '/api/two-factor/send-email-login'
cs-method:
- 'POST'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-43914 | Auth Bypass | Vaultwarden versions prior to 1.35.4 |
| CVE-2026-43914 | Auth Bypass | Vaultwarden vulnerable function: send_email_login (email.rs) |
| CVE-2026-43914 | Auth Bypass | Vaultwarden vulnerable API endpoint: /api/two-factor/send-email-login |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 12, 2026 at 02:20 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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