CVE-2025-55001

Executive Summary

CVE-2025-55001 is a security vulnerability in OpenBao, a secrets management solution. The vulnerability allows an attacker to bypass MFA (Multi-Factor Authentication) requirements by exploiting improper normalization of usernames when the username_as_alias=true parameter is used in the LDAP auth method. This can lead to unauthorized access to sensitive data, including secrets, certificates, and keys.

Supply Chain & Package Security

OpenBao is a Go-based project. The vulnerability affects the LDAP authentication plugin. The fix is available in version 2.3.2. Users should update to this version immediately. The vulnerability does not affect the core OpenBao binary but rather the LDAP auth method plugin.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

The threat level is considered medium due to the potential for unauthorized access to sensitive data, but the impact is limited to MFA bypass.

Deep Dive & Mechanics

The vulnerability exists in the LDAP authentication method of OpenBao. When username_as_alias=true is configured, the username provided by the caller is used verbatim as the entity alias. This alias is then used for policy and MFA attribution. An attacker can supply a username that matches an existing entity alias (e.g., by using case variations or special characters) to bypass MFA requirements.

For example, if an entity alias is "admin", an attacker could supply "Admin" or "admin " (with a trailing space) to match the alias and bypass MFA. The lack of normalization (e.g., lowercasing, trimming) allows this bypass.

Vulnerable vs. Patched Code

Vulnerable Code (<= 2.3.1):

// In the LDAP auth method, the username is used directly as the alias
alias := username

Patched Code (>= 2.3.2):

// Normalize the username before using it as an alias
alias := strings.ToLower(strings.TrimSpace(username))

The patch ensures that the username is normalized (lowercased and trimmed) before being used as an entity alias, preventing MFA bypass.

Exploitation & Lab Setup

Red Team

1. Setup: Deploy OpenBao 2.3.1 with LDAP auth method configured with username_as_alias=true.
2. Create Entity Alias: Create an entity alias "admin" with MFA requirements.
3. Exploit: Use an LDAP client to authenticate with a username like "Admin" or "admin " (with a trailing space).
4. Result: The authentication succeeds without MFA, granting access to the "admin" entity's policies.

Example LDAP authentication request:

curl -k -X POST https://openbao.example.com/v1/auth/ldap/login \
  -H "Content-Type: application/json" \
  -d '{"password": "attacker_password", "username": "Admin"}'

Blue Team

1. Detection: Monitor for LDAP authentication attempts with usernames that differ from the expected entity aliases (e.g., case variations, trailing spaces).
2. Mitigation: Update to OpenBao 2.3.2 or later.
3. Workaround: Remove username_as_alias=true from the LDAP auth method configuration and update entity aliases accordingly.

Indicators of Compromise (IOCs)

• Log Entries: LDAP authentication logs showing successful logins with usernames that do not match the expected entity alias format.
• Network Traffic: LDAP authentication requests with unusual username patterns (e.g., mixed case, trailing spaces).
• System Changes: Unauthorized access to secrets or policies that should have been protected by MFA.

Detection Engineering

YARA Rule

rule CVE_2025_55001_OpenBao_LDAP_Bypass {
    meta:
        description = "Detects LDAP authentication attempts with non-normalized usernames in OpenBao logs"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-55001"
    strings:
        $log_entry = /LDAP login attempt with username: [A-Za-z0-9_]+/
        $non_normalized = /[A-Z]| $/
    condition:
        $log_entry and $non_normalized
}

Sigma Rule

title: OpenBao LDAP MFA Bypass via Non-Normalized Username
id: cve-2025-55001
status: experimental
description: Detects LDAP authentication attempts with non-normalized usernames in OpenBao logs
author: Valters IT
date: 2025-04-10
logsource:
    product: openbao
    service: audit
detection:
    selection:
        event: "LDAP login attempt"
        username|contains|any:
            - " "
            - "A"
            - "B"
            - "C"
            - "D"
            - "E"
            - "F"
            - "G"
            - "H"
            - "I"
            - "J"
            - "K"
            - "L"
            - "M"
            - "N"
            - "O"
            - "P"
            - "Q"
            - "R"
            - "S"
            - "T"
            - "U"
            - "V"
            - "W"
            - "X"
            - "Y"
            - "Z"
    condition: selection
falsepositives:
    - Legitimate users with uppercase usernames
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-55001 OpenBao LDAP MFA Bypass"; flow:to_server; content:"POST"; http_method; content:"/v1/auth/ldap/login"; http_uri; content:"username"; nocase; pcre:"/username\":\"[A-Z]/"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Update OpenBao to version 2.3.2 or later.
2. Workaround: Remove username_as_alias=true from the LDAP auth method configuration and update entity aliases accordingly.
3. Monitoring: Enable audit logging and monitor for LDAP authentication attempts with non-normalized usernames.
4. Access Control: Review and restrict access to the LDAP auth method.

Valters IT
Securing Digital Frontiers