Listen to this Post
CVE-2025-13593: Origin Validation Flaw Enables Arbitrary File Write During Installation
This vulnerability resides in Synology ActiveProtect Agent versions prior to 1.1.0-0439, a component used in Windows environments for data backup and recovery. At its core, the issue is an origin validation error (CWE-346), meaning the installation process fails to properly verify the authenticity and source of files being written to the system. This oversight allows a local, unprivileged user to manipulate the software installation procedure to write arbitrary files, albeit with restricted content.
The vulnerability’s exploitation vector is local, requiring the attacker to have prior access to the target machine. During the installation of the ActiveProtect Agent, the process typically runs with elevated privileges. The installation logic contains a path validation flaw, which an attacker can bypass to write files to sensitive directories, such as system folders (e.g., C:\Windows\System32\).
The flaw can be triggered by placing a malicious file in a location the installer will process. Because the installer fails to check the file’s origin correctly, it copies the payload to the target directory with system-level privileges. The content of the written files is “restricted,” which suggests that while the payload may not be arbitrary, it likely still allows for the creation of scripts, configuration overrides, or other data that can lead to privilege escalation or persistence.
Organizations using the affected software face a significant risk. An attacker who has gained initial low-privileged access (e.g., through a separate vulnerability) can use this flaw to elevate their privileges to SYSTEM, effectively taking full control of the host. This can lead to further network compromise, data exfiltration, or installation of persistent backdoors.
DailyCVE Form:
Platform: Windows
Version: before 1.1.0-0439
Vulnerability : Arbitrary file write
Severity: Medium (CVSS 6.1)
date: May 27, 2026
Prediction: Released (Nov 24, 2025)
(end of form)
What Undercode Say:
For demonstration and detection purposes, security analysts can use the following commands to verify a system’s exposure or to simulate a detection scenario.
Check the current version of Synology ActiveProtect Agent
wmic product where "name like 'ActiveProtect Agent%%'" get version
Alternatively, check version in Registry
reg query "HKLM\SOFTWARE\Synology\ActiveProtect Agent" /v Version
Detection: Monitor for unauthorized file creation in system folders during installation
powershell -c "Get-WinEvent -FilterHashtable @{LogName='Setup'; ID=}"
Exploit:
A Proof-of-Concept (PoC) for this vulnerability would involve an attacker placing a payload and then triggering the installation routine. An example approach is:
1. Place Malicious Script: The attacker saves a script (e.g., evil.bat) containing malicious commands to a location accessible during the install, like C:\ProgramData\Synology\install_manifest.tmp.
2. Trigger Installation: The attacker then invokes the installer with elevated privileges using a technique like `PsExec` or scheduled tasks.
3. Bypass Validation: The installer’s flawed origin validation processes the attacker’s folder, believing it to be a legitimate source, and copies `evil.bat` to the target path (e.g., C:\Windows\System32\evil.bat).
4. Gain Persistence: The attacker uses the written file to maintain access, for instance by creating a registry run key: reg add HKLM\Software\Microsoft\Windows\CurrentVersion\Run /v UpdateService /t REG_SZ /d "C:\Windows\System32\evil.bat".
Protection:
Immediate Patching: Upgrade the Synology ActiveProtect Agent to version 1.1.0-0439 or higher. The vendor has officially released this update to fix the origin validation flaw.
Restrict Local Access: Enforce the principle of least privilege (PoLP). Limit local user access to installation and sensitive system processes to mitigate potential exploit attempts.
Enable Enhanced Logging: Monitor Windows Setup event logs (Event ID 11707, 11724) for unexpected installation activities or file modifications that could indicate an exploit.
Application Control: Implement AppLocker or Windows Defender Application Control policies to block unauthorized or unsigned installation packages.
Impact:
Successful exploitation of this vulnerability (CVE-2025-13593) allows a local, low-privileged attacker to write arbitrary files with limited content to any location on the system. This can lead to the following severe outcomes:
Privilege Escalation: The attacker can elevate their privileges from a local unprivileged user to SYSTEM (the highest privilege level on Windows), enabling full control over the host OS.
Persistent Backdoor: The arbitrary file write can be used to install a persistent backdoor, surviving reboots and system updates, by writing a script that runs at startup or creating a scheduled task.
System Integrity Compromise: The ability to write to system directories (e.g., C:\Windows\System32\) allows an attacker to replace critical system binaries or configuration files, leading to system instability or a supply chain attack.
Lateral Movement: After compromising a single host, the attacker could use it as a pivot point to move laterally across the network, targeting other vulnerable systems or sensitive servers.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
