A newly disclosed vulnerability in WinRAR, the widely used Windows file compression utility, has sparked serious concern in the cybersecurity community due to its ability to bypass Microsoft’s “Mark of the Web” (MotW) security mechanism. Tracked as CVE-2025-31334, this flaw enables attackers to execute arbitrary code from internet-delivered files without triggering Windows security prompts, significantly increasing the risk of silent malware delivery via crafted archive files.
The vulnerability affects all versions of WinRAR prior to 7.11, and users are urged to upgrade immediately.
🔍 What Is “Mark of the Web” and Why It Matters
Mark of the Web (MotW) is a Windows security mechanism that tags files originating from the internet with metadata (Zone.Identifier). When users try to open these files—especially executable content—Windows displays a security warning, giving the user a chance to cancel the operation. This is often the final layer of user-facing defense against malware disguised as legitimate content.
MotW is frequently leveraged by endpoint protection platforms and security policies to block or alert on high-risk file execution.
🕳️ Vulnerability Breakdown: CVE-2025-31334
➤ Nature of the Flaw:
The vulnerability involves how WinRAR handles symbolic links (symlinks) embedded in archive files. If an attacker includes a symlink that points to a local or embedded executable, and the user opens it via the WinRAR shell, MotW is ignored, and the executable runs without warning.
➤ Impact:
- Eliminates the MotW-based user prompt or warning.
- Allows stealthy execution of malware in phishing campaigns.
- Evades many endpoint security policies reliant on MotW.
➤ Technical Specifics:
- Windows symlinks to executables can be added to
.rararchives. - When launched from WinRAR, the executable bypasses MotW protections.
- The issue arises from WinRAR not properly inheriting or validating Zone.Identifier metadata for linked executables.
🧪 Real-World Exploitation Example: Spear-Phishing via WinRAR
🎯 Attack Scenario: Silent Malware Execution via Email
Step 1: Crafting the Payload
- Attacker creates a malicious executable
payload.exe, which may contain ransomware, a remote access trojan (RAT), or info-stealing malware. - They create a symbolic link (e.g.,
Invoice.pdf.exe) pointing topayload.exe, and embed it in a.rararchive.
Step 2: Delivering the Bait
- The attacker sends a spear-phishing email with the
.rarattachment: “Please review the attached invoice and confirm payment details by Friday.”
Step 3: Execution Without Warning
- The user opens the
.rarin WinRAR and double-clicksInvoice.pdf.exe. - No MotW warning is shown, and the payload silently executes.
- Malware can now:
- Connect to a command-and-control server.
- Deploy additional payloads.
- Initiate data exfiltration or privilege escalation.
Why it works: MotW is bypassed because WinRAR fails to inherit security metadata from the archive when executing symlinks.
🧯 Patch and Disclosure Timeline
- Discovered by: Shimamine Taihei of Mitsui Bussan Secure Directions, coordinated via Japan’s IPA (Information-Technology Promotion Agency) and CSIRT.
- Patched in: WinRAR version 7.11
- Changelog note: “If symlink pointing at an executable was started from WinRAR shell, the executable Mark of the Web data was ignored.”
🔐 MotW Bypasses: A Recurring Tactic
This vulnerability mirrors recent trends:
- In 2024, a similar flaw in 7-Zip was exploited by Russian APT groups to deliver SmokeLoader malware using multi-layered archives.
- MotW bypasses are attractive to attackers because they neutralize user awareness, an essential component of modern endpoint defense.
✅ Recommendations for Security Teams
| Action | Description |
|---|---|
| 🔄 Update to WinRAR v7.11+ | Patch immediately across all systems. This version contains the fix for CVE-2025-31334. |
| 🔍 Detect archive-based symlinks | Use EDR/XDR to flag .rar files that contain symbolic links to .exe files. |
| 🚫 Restrict .rar execution contexts | Prevent execution of files directly from within archive tools. Force users to extract first. |
| 🧱 Enforce MotW handling policies | Use Group Policy or AppLocker to block unsigned files with MotW tags from executing. |
| 📢 User awareness training | Educate users on file extensions, phishing tactics, and risky archive behavior. |
CVE-2025-31334 in WinRAR is yet another example of how legacy file-handling tools can become modern threat vectors. The flaw allows attackers to exploit symbolic link behavior and MotW limitations to deliver malware without any warning or user suspicion.
As threat actors continue to chain flaws and bypass traditional protections, defenders must look beyond perimeter defenses and apply detection and hardening at the application layer—especially for widely used utilities like WinRAR.
Information security specialist, currently working as risk infrastructure specialist & investigator.
15 years of experience in risk and control process, security audit support, business continuity design and support, workgroup management and information security standards.
