CVE-2025-49113: Roundcube Post-Auth Remote Code Execution (RCE)

CVE-2025-49113: Roundcube Post-Auth Remote Code Execution (RCE)

01 September 2025

CVE-2025-49113: Roundcube Post-Auth Remote Code Execution (RCE) – Deep Technical Analysis

CVE-2025-49113 is a critical post-authentication Remote Code Execution (RCE) vulnerability discovered in Roundcube Webmail. The issue arises from the _from parameter in program/actions/settings/upload.php not being properly validated, allowing PHP Object Deserialization attacks.

Authenticated users can send crafted input to execute code remotely on the Roundcube server.

1️⃣ Role of the _from Parameter

The upload.php script handles user settings file uploads. The _from parameter indicates the source of the file or data.

However, it is poorly validated and passed directly to unserialize(), creating an object injection attack surface.

2️⃣ Technical Mechanism

// roundcube/upload.php (simplified)
$from = $_REQUEST['_from'] ?? '';
$data = unserialize($from); // user input is deserialized directly

unserialize() processes attacker-controlled input → triggers __wakeup() or __destruct() methods in PHP classes → remote code execution.

3️⃣ PoC-Style Demo (Educational)

<?php
// insecure.php - educational demo (NOT a real exploit)
class Evil {
    public function __destruct() {
        echo "[*] __destruct() triggered! Imagine system('id'); here...\n";
    }
}

$input = $_GET['data'] ?? '';
$unser = unserialize($input);
?>

Attacker request:

GET /insecure.php?data=O:4:"Evil":0:{} HTTP/1.1
Host: localhost

Result: Evil::__destruct() is triggered → payload runs.

4️⃣ Exploit Flow (Step by Step)

  1. Authenticate → Attacker logs in with valid credentials or stolen session.
  2. Send Request → Target upload.php with crafted _from serialized payload.
  3. Deserialize Triggered → Roundcube unserializes the object.
  4. Magic Method Executes → Command runs on the server.

5️⃣ Payload Logic

A typical RCE payload works as follows:

  • PHP object is created.
  • __destruct() or __wakeup() methods call system() / exec() / file_put_contents().
  • unserialize() triggers these methods → code executes.

Example pseudo-payload structure:

O:8:"ExploitX":1:{s:4:"cmd";s:8:"id > /tmp/pwned";}

(For educational purposes only, not a working exploit.)

6️⃣ Red-Team Test Scenario

Curl-Based Check

curl -X POST http://target/roundcube/program/actions/settings/upload.php   -d '_from=O:8:"ExploitX":0:{}'   -b 'roundcube_sessid=VALID_SESSION'

Node.js Automated Test Script

import fetch from 'node-fetch';

const payloads = [
  'O:8:"ExploitX":0:{}',
  'O:5:"TestX":0:{}'
];

async function scan() {
  for (const p of payloads) {
    const res = await fetch('http://target/roundcube/program/actions/settings/upload.php', {
      method: 'POST',
      headers: { 'Cookie': 'roundcube_sessid=VALID_SESSION' },
      body: `_from=${encodeURIComponent(p)}`
    });
    console.log(`[+] Sent payload: ${p}, Status: ${res.status}`);
  }
}

scan();

7️⃣ Hacker Perspective

  • Post-auth means first compromise the account, then execute code.
  • unserialize() = red alert; a golden opportunity for attackers.
  • This bug can lead to domain-wide compromise in mail servers.
  • Exploit code is already public (Metasploit / Exploit-DB). If unpatched → high risk.

8️⃣ Mitigation & Defense

  • Patch: Update Roundcube → 1.5.10 / 1.6.11 or later.
  • Log monitoring: Watch for _from= unusual requests.
  • WAF rules: Block unserialize patterns (e.g., O:\d+:).
  • Harden system: Limit webmail process privileges.
  • Credential hygiene: Post-auth exploitation highlights credential reuse risks.

9️⃣ Indicators of Compromise (IOC)

🔎 Web Server Log Anomalies

  • upload.php requests with _from parameter.
  • O:\d+: or s:\d+: patterns in query strings / POST bodies.

Example Nginx/Apache log:

192.168.1.100 - - [01/Sep/2025:17:10:22 +0000] "POST /roundcube/program/actions/settings/upload.php HTTP/1.1" 200 532 "-" "curl/7.88.1" "_from=O:8:"ExploitX":0:{}"

🔎 File System Anomalies

  • Unexpected .php files in /tmp, /var/tmp, or webroot.
  • New cron jobs in /var/spool/cron/*, /etc/cron.*/*.

🔎 Process Anomalies

  • bash, sh, perl, python, nc processes running as www-data or apache.
  • Unexpected shell processes seen in ps aux | grep apache.

🔎 Network IOC

  • Outbound connections via nc, curl, wget on non-standard ports.
  • IDS/IPS logs with base64 encoded commands or suspicious user-agent strings.

🔟 Incident Response Checklist (Deep-Dive)

🛑 1. Isolation

  • Disconnect server from network.
  • Acquire RAM dump for live forensic (avml, lime).

📂 2. Log Analysis

  • grep -R "_from=" /var/log/nginx/ to detect attack attempts.
  • zgrep -E "O:[0-9]+:" /var/log/nginx/access.log* to identify serialized objects.
  • Check Roundcube logs/errors.log for unexpected unserialize errors.

🧾 3. File System Scanning

  • Modified files in the last 7 days: find /var/www/html/roundcube -type f -mtime -7 -ls
  • Backdoor scan: grep -R "base64_decode(" /var/www/html/roundcube and grep -R "eval(" /var/www/html/roundcube

🖥️ 4. Process & Persistence Check

  • Unexpected processes: ps -eo user,pid,cmd | grep -E "nc|bash|perl|python"
  • Cron/backdoor check: crontab -l -u www-data and cat /etc/cron.*/* | grep curl

🌐 5. Network Analysis

  • Live connections: netstat -antp | grep www-data, lsof -i -n -P | grep php
  • Reverse shell IOC: ESTABLISHED connections on non-80/443 ports.

🩺 6. IOC Correlation

  • Match IPs against Threat Intel (AbuseIPDB, AlienVault OTX).
  • Feed into SIEM and check if the same IP was involved in other attacks.

🔐 7. Eradication & Recovery

  • Clean rebuild of the server.
  • Update Roundcube → 1.5.10 / 1.6.11.
  • Enable SELinux/AppArmor.
  • Reset all user passwords.

📢 8. Lessons Learned

  • Credential hygiene is critical.
  • Combine brute-force / weak password detection with MFA.


📺 Video Demonstration