The disclosure of CVE-2023-38831, a zero-day vulnerability in WinRAR that was actively exploited against cryptocurrency traders in August 2023, highlighted a persistent weakness in how many users handle archived files. The vulnerability allowed attackers to craft RAR archives that displayed legitimate files while executing hidden malicious code upon extraction. With Bitcoin trading around $26,000 at the time, traders downloading what appeared to be trading tools or market analysis documents found their wallets drained instead. This guide walks through practical steps anyone can take to verify archive files before opening them, using both built-in operating system tools and free security utilities.
Step 1: Verify the Source
Before downloading any archive file, confirm the source is legitimate. Check the URL of the download page — does it match the official domain exactly? Attackers frequently use lookalike domains that differ by a single character or use alternative top-level domains. If the file arrives via email, verify the sender’s full email address, not just the display name. A message appearing to come from a well-known crypto exchange might actually originate from a spoofed address.
For files shared in Telegram groups, Discord servers, or other messaging platforms, be especially cautious. The social proof of seeing others in a group share files does not guarantee safety. Cross-reference any download link by searching for the official website independently rather than clicking the shared link directly.
Step 2: Check File Hashes
If the legitimate source provides a hash value for the file, always verify it before opening. A hash is a fixed-length string generated by running the file through a cryptographic algorithm like SHA-256. If even a single byte of the file has been modified, the hash will be completely different.
On Windows, open PowerShell and run:
Get-FileHash -Algorithm SHA256 path\to\file.rar
On macOS and Linux, open Terminal and run:
shasum -a 256 /path/to/file.rar
Compare the output to the hash published on the official website. If they match, the file has not been tampered with during download. If the source does not provide a hash, that itself is a warning sign for security-sensitive software.
Step 3: Scan Before Extracting
Run a malware scan on the archive file before extracting its contents. Windows Defender, which is built into Windows 10 and 11, can scan individual files by right-clicking the file and selecting “Scan with Microsoft Defender.” For more thorough coverage, upload the file to VirusTotal.com, which scans uploads against more than 70 antivirus engines simultaneously.
Be aware that no antivirus solution catches everything, especially zero-day exploits. The WinRAR vulnerability was being actively exploited before any antivirus engine detected it. Scanning is a necessary but not sufficient precaution — it reduces risk but does not eliminate it.
For cryptocurrency users specifically, consider maintaining a dedicated quarantine machine or virtual machine for opening untrusted files. A free VirtualBox installation running a fresh copy of Linux provides an isolated environment where malware cannot access your primary operating system or browser wallets.
Step 4: Inspect Archive Contents
Before extracting, open the archive in your file manager or archive tool and examine its contents carefully. Look for files with double extensions like report.pdf.exe or analysis.xlsx.scr. Check for files that have no business being in the archive, such as executables, scripts, or batch files when you expected only documents or images.
Pay attention to file sizes. A small text file that appears as several megabytes in the archive may have hidden content. Compression ratios that seem unusual for the file types involved — for example, a PDF that compresses to 10 percent of its original size — warrant additional scrutiny.
In the case of CVE-2023-38831, the malicious WinRAR archives contained a legitimate file alongside a hidden folder with the same name that held the malicious payload. The exploit manipulated how WinRAR rendered the archive contents to hide the malicious folder from the user’s view.
Step 5: Keep Software Updated
The WinRAR zero-day was patched in version 6.23, released on August 19, 2023. If you use WinRAR, ensure you are running version 6.23 or later. More broadly, keep all archive software updated to the latest version. Enable automatic updates where available, and periodically check for updates manually for software that does not auto-update.
Consider whether you actually need WinRAR at all. Modern operating systems include built-in support for ZIP files, and free alternatives like 7-Zip have a strong security track record. Reducing the number of archive utilities you use reduces your attack surface. If you must use WinRAR for RAR format compatibility, at minimum ensure it is the current version.
Step 6: Additional Protections for Crypto Users
Cryptocurrency users face elevated risk because their devices often control significant financial assets. Beyond the general precautions above, consider these additional measures. Use a hardware wallet for storing significant cryptocurrency holdings. Hardware wallets keep private keys on a dedicated secure device that cannot be accessed by malware on your computer, even if that computer is fully compromised.
Separate your browsing and crypto activities from your general computing. Use a dedicated browser profile or even a separate device for accessing cryptocurrency exchanges and wallets. This reduces the chance that a malicious file opened on your general-purpose account can access your crypto accounts.
Enable all available security features on your cryptocurrency exchange accounts: hardware security key authentication, withdrawal whitelist restrictions, and anti-phishing codes. These measures create additional layers of defense that can protect your funds even if your device is compromised through a malicious archive file.
Summary
Archive files remain a common attack vector precisely because they are so widely used and trusted. The WinRAR zero-day demonstrated that even well-established software can harbor exploitable vulnerabilities for months before discovery. By following a consistent verification workflow — checking the source, verifying hashes, scanning before extraction, inspecting contents, keeping software updated, and maintaining dedicated security for crypto assets — you can significantly reduce the risk of falling victim to similar attacks in the future.
Disclaimer: This article is for educational purposes only and does not constitute professional security advice. Always consult with qualified cybersecurity professionals for specific threat assessments.
good guide but honestly the best defense is just dont download archives from random telegram groups. that eliminates 90 percent of the risk right there
hard agree on not downloading from telegram. but the CMC supply chain attack showed even legit sites can serve malware. verification tools are mandatory now
the CMC supply chain attack is exactly why verification tools matter but also why no single method is enough. layered security or nothing
the hash verification step is crucial and most people skip it. takes 30 seconds to verify a sha256 checksum
the CVE-2023-38831 WinRAR exploit was especially nasty because it showed a legitimate file alongside the hidden script. no visual clue anything was wrong
the hash verification step is the most important part of this guide. if traders spent 30 seconds checking SHA256 before extracting theyd save themselves a lot of grief
hash verification only works if you trust the source of the hash itself. a compromised website serves both the malware and the matching fake hash
CVE-2023-38831 was nasty because the malicious files looked identical to legitimate ones. visual inspection was completely useless