CriticalCVE-2018-20250

    WinRAR Absolute Path Traversal Vulnerability (CVE-2018-20250)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    In WinRAR versions prior to and including 5.61, There is path traversal vulnerability when crafting the filename field of the ACE format (in UNACEV2.dll). When the filename field is manipulated with specific patterns, the destination (extraction) folder is ignored, thus treating the filename as an absolute path.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Check Point Software Technologies WinRAR eq All versions prior and including 5.61..All versions prior and including 5.61

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    96.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.88

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    243.81 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

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    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

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    7.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    96.0 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.88
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 14 February 2022
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-36

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw requires user interaction and local execution, but exploitation is trivial. A single crafted archive drops attacker code into the startup folder for persistent execution under the user's context, with no authentication required. That makes it an ideal initial-access vector for phishing campaigns. Public exploits have circulated for years, it sits among the CVEs most likely to be exploited, and CISA flags its use in ransomware campaigns. The main exposure is office workstations in estates with unmanaged software, where WinRAR often goes unpatched for years. Treat any instance of version 5.61 or earlier, and any presence of UNACEV2.dll, as a high-priority finding to remediate within 24 hours.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory WinRAR: Use EDR or software distribution tooling to find every endpoint running WinRAR.exe at version 5.61 or earlier. Include portable copies in user profiles. Example KQL: DeviceTvmSoftwareInventory | where SoftwareName has "winrar".
      • Deploy the fix: Update to the current WinRAR release. RARLAB removed ACE support entirely in WinRAR 5.70. Confirm the exact version in the vendor advisory, and push the latest build rather than stopping at 5.70.
      • Delete UNACEV2.dll wherever updating is not immediately possible. Remove it from the WinRAR install directory (e.g. C:\Program Files\WinRAR\) or block it via GPO/AppLocker. This kills ACE extraction outright.
      • Hunt for third-party copies: Search hosts for UNACEV2.dll. Other archivers and utilities bundle the same library, so remove or update any affected tools.
      • Check startup folders for compromise: Review %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup and C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp for unknown EXE, LNK, VBS or BAT files created shortly after an archive was opened. Isolate any hosts with hits.

    2. Runbook step 2

      Mitigation layers

      • Mail and web gateway: Block .ace attachments. Also use content inspection to detect the ACE signature **ACE** at byte offset 7 and quarantine matches, even when the file is disguised as .rar, .zip or .7z. Public exploits rely on renamed ACE files.
      • Application control: Use AppLocker or WDAC to prevent loading of UNACEV2.dll and execution of binaries from startup folders and %APPDATA%. Allow only signed, approved paths.
      • Endpoint hardening: Enable the Defender ASR rule "Block executable files from running unless they meet a prevalence, age, or trusted list criterion". Add an EDR policy that blocks WinRAR.exe from writing to autostart locations.
      • Standardisation: Replace WinRAR with built-in Windows extraction or a centrally managed archiver where feasible. Remove local admin rights so users cannot reinstall outdated versions.
      • User awareness: Issue a short-term warning about archives from unknown email senders or downloads. Typical lures include fake CVs, invoices and documents.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 11 (FileCreate): Alert when Image ends with \WinRAR.exe and TargetFilename contains \Start Menu\Programs\Startup\. Sigma shape: selection: Image|endswith: '\WinRAR.exe' AND TargetFilename|contains: '\Programs\Startup\'.
      • Sysmon EID 7 (ImageLoad): Flag any process loading UNACEV2.dll. After the rollout this should never fire, so every hit is suspicious. KQL: DeviceImageLoadEvents | where FileName =~ "UNACEV2.dll".
      • Process ancestry at logon: Correlate processes launched by explorer.exe from a startup folder whose file was recently written by WinRAR.exe. Join Sysmon EID 1 and EID 11 on hash and path.
      • YARA on gateways and file shares: Match $ace = "**ACE**" at offset 7 together with filename fields containing C:\ or ..\ plus Startup. Run the rule retroactively against mail archives as well.
      • Windows Security EID 4663 / Defender telemetry: Monitor writes to autostart folders by non-installer processes. Correlate these with preceding Outlook or browser downloads.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    In WinRAR versions prior to and including 5.61, There is path traversal vulnerability when crafting the filename field of the ACE format (in UNACEV2.dll). When the filename field is manipulated with specific patterns, the destination (extraction) folder is ignored, thus treating the filename as an absolute path.

    Source: CISA KEV Catalog, cvelistv5, NVD (NIST)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Check Point Software Technologies Ltd.WinRAR
    • All versions prior and including 5.61
    • —
    rarlabwinrar
    • ≤ 5.61
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-36Absolute Path Traversal

      Base

      The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize absolute path sequences such as "/abs/path" that can resolve to a location that is outside of that directory.

      Entry at MITRE CWE-36

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Metasploit FrameworkMetasploit: exploit/windows/fileformat/winrar_ace (opens in a new tab)rapid7.comweaponized (Metasploit module)reported, not verified—
    GitHubblau72/CVE-2018-20250-WinRAR-ACE (opens in a new tab)github.comPoC (publicly reported)reported, not verified—
    Packet StormRARLAB WinRAR ACE Format Input Validation Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Exploit-DBEDB-ID 46552 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—
    Exploit-DBEDB-ID 46756 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

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