Summary
CVE20258088 is a Windowsonly WinRAR pathtraversal bug that uses NTFS alternate data streams (ADSes) in crafted RAR files to drop hidden payloads (DLLs, EXEs, LNKs) outside the chosen extraction folder (e.g., %TEMP%, %LOCALAPPDATA%, Startup) so they can run and persist. Discovered by ESET in midJuly 2025 and seen in targeted phishing, it was fixed in WinRAR 7.13 (30 July 2025); exploitation requires the user to open or extract the archive and needs no special privileges.
Urgent Actions Required
- Update WinRAR to 7.13 on all Windows machines.
- Don’t open RAR attachments from unknown senders.
- Extract suspicious RARs only in a sandbox or isolated VM.
- Check %TEMP%, %LOCALAPPDATA%, and Startup for unexpected .dll, .exe, or .lnk files.
- Strengthen email filters to block or quarantine RAR attachments.
Which Systems Are Vulnerable to CVE20258088?
Technical Overview
- Vulnerability Type: Path Traversal via Alternate Data Streams (ADSes) in crafted RAR archives
- Affected Software/Versions:
- WinRAR (Windows) ≤ 7.12
- Windows builds of RAR, UnRAR, UnRAR.dll, and portable UnRAR source code
- Attack Vector: Local file extraction by user (archive delivered via phishing/email or other means)
- CVSS Score: 8.4
- CVSS Vector: CVSS:3.1
- Attack Vector: Local
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: Required
- Scope: Unchanged
- Confidentiality Impact: High
- Integrity Impact: High
- Availability Impact: High
- Patch Availability: Yes, available[2]
How Does the CVE-2025-8088 Exploit Work?
The attack typically follows these steps:
What Causes CVE-2025-8088?
Vulnerability Root Cause:
WinRAR didn’t sanitize archive paths (including ADS), letting crafted RARs drop hidden payloads outside the chosen folder (e.g., %TEMP%, %LOCALAPPDATA%, Startup) for silent execution.
How Can You Mitigate CVE-2025-8088?
If immediate patching is delayed or not possible:
- Open suspicious RARs only in sandboxed environments.
- Block or quarantine RAR attachments from unknown senders.
- Check %TEMP%, %LOCALAPPDATA%, and Startup for unexpected .exe, .dll, or .lnk files.
- Scan for known malicious files by SHA1 or filename.
- Update software using UnRAR.dll or portable UnRAR to the latest version.
- Train users to avoid RARs from untrusted sources.
Which Assets and Systems Are at Risk?
Asset Types Affected:
- Windows systems with WinRAR versions up to 7.12 installed.
- Applications or tools relying on UnRAR.dll or the portable UnRAR source code.
Business-Critical Systems at Risk:
- Devices regularly used to extract RAR archives.
- Corporate environments where malicious archives could drop payloads into Startup or system directories, enabling persistent malware.
Exposure Level:
- Internet-facing email clients or file-sharing systems where users receive RAR attachments.
- Internal networks where unpatched WinRAR versions are in use, allowing targeted phishing attacks to succeed.
- Any system where users have write access to %TEMP%, %LOCALAPPDATA%, or Startup folders, since payloads could execute automatically.
How Can You Detect CVE-2025-8088 Exploitation?
Exploitation Signatures:
- RAR attachments delivered via spearphishing (resume / jobapplication lures).
- Archives containing a visible decoy file plus hidden NTFS Alternate Data Stream (ADS) entries.
- Extraction that results in files being written outside the chosen destination (e.g., Startup, %TEMP%, %LOCALAPPDATA%).
Behavioral Indicators:
- Hidden ADS payloads are deployed to %TEMP%, %LOCALAPPDATA%, or Startup during extraction
- .lnk shortcuts placed in Startup execute on user login.
- Dropped DLLs may be loaded (COM/CLSID techniques were observed) to decrypt and run shellcode.
Alerting Strategy:
- Priority: Critical for endpoints with WinRAR ≤ 7.12.
Alert triggers:
- Creation of new .lnk, .dll, or .exe files in Startup, %TEMP%, or %LOCALAPPDATA% immediately following RAR extraction.
- Detection of the listed sample SHA1s or filenames on endpoints.
- Execution of unexpected processes that were unpacked from a recently extracted RAR archive.
Remediation & Response
Mitigation Steps if No Patch:
- Apply SRP + IFEO to block winrar.exe, rar.exe, and unrar.exe.
- Uninstall or disable WinRAR on systems that cannot be patched.
- Restrict extraction to userwritable folders only; do not extract to system or Startup paths.
- Extract suspicious RAR files only in sandboxed or isolated VMs.
- Strengthen email filtering to block or quarantine RAR attachments (particularly resume/jobapplication lures).
- Update any software that embeds UnRAR.dll or uses the portable UnRAR source.
- Scan systems for the example SHA1s and filenames provided in the references and remove matches.
Compliance & Governance Notes
Standards Impacted:
- CISA KEV / BOD2201 – CVE20258088 is listed as a known exploited vulnerability.
Audit Trail Requirement:
- Record patch deployment details: date, time, and target hosts for WinRAR 7.13.
Policy Alignment:
- Ensure timely application of WinRAR 7.13 to address CVE20258088.
Where Can I Find More Information on CVE-2025-8088?
CVSS Breakdown Table
| Metric | Value | Description |
|---|---|---|
| Base Score | 8.4 | High severity indicating critical impact and exploitability |
| Attack Vector | Local | Exploit requires local access (e.g., opening/extracting the archive) |
| Attack Complexity | Low | Exploit does not require special conditions |
| Privileges Required | None | No elevated or special privileges needed |
| User Interaction | Required | Victim must open or extract the malicious RAR file |
| Scope | UnChanged | Impact limited to the vulnerable component (WinRAR/UnRAR) |
| Confidentiality Impact | High | Exploit can expose sensitive files or data |
| Integrity Impact | High | Exploit can write unauthorized files (DLLs, executables) |
| Availability Impact | High | Exploit can affect system integrity and persistence |
