CriticalCVE-2013-2551

    Microsoft Internet Explorer Use-After-Free Vulnerability (CVE-2013-2551)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Use-after-free vulnerability in Microsoft Internet Explorer 6 through 10 allows remote attackers to execute arbitrary code via a crafted web site that triggers access to a deleted object, as demonstrated by VUPEN during a Pwn2Own competition at CanSecWest 2013, aka "Internet Explorer Use After Free Vulnerability," a different vulnerability than CVE-2013-1308 and CVE-2013-1309.

    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
    • Microsoft Internet Explorer 11 eq 6..6
    • Microsoft Internet Explorer 11 eq 7..7
    • Microsoft Internet Explorer 11 eq 8..8
    • Microsoft Internet Explorer 11 eq 9..9
    • Microsoft Internet Explorer 11 eq 10..10

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

    Metrics

    8.8

    Priority

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

    Source: NVD, CVSS v3

    8.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    73.9 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.48

    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
    248.17 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.

    Read in glossary
    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.

    Read in glossary
    8.8 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
    8.8
    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“.

    Read in glossary
    73.9 %
    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
    99.48
    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 7 February 2025
    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-416

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This bug is network-reachable without authentication, needs only a visit to a malicious page, and was a staple of mass-market exploit kits in drive-by campaigns for years. CISA explicitly flags known ransomware use, and its exploitation likelihood sits at the very top of the scale. On modern, maintained clients the risk is effectively closed. It remains acute in KRITIS and industrial environments with frozen legacy systems (OT HMIs, medical devices, specialist applications on Windows 7/XP) that still have internet or proxy access. Treat any such web-capable IE 6–10 host as immediately exploitable and fix it first; fully air-gapped instances can follow your planned decommissioning schedule.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Find exposed hosts: Identify every host still running Internet Explorer 6–10 via asset inventory, SCCM/Intune, or proxy logs (user agent MSIE 6.0 through MSIE 10.0). Expect legacy estates: Windows XP/Vista/7/Server 2003/2008, embedded OT/HMI boxes, medical devices, and POS terminals.
      • Patch: Apply the vendor's cumulative IE security update. The flaw sits in the VML component vgx.dll and was addressed in bulletin MS13-037 (May 2013); look up the exact KB per OS/IE version in the vendor advisory. The durable fix is moving to a supported browser, because IE 6–10 is out of support.
      • Cut internet access for unpatchable hosts: Block direct web access for any host that cannot be patched today. Allow only allow-listed destinations via the proxy, since exploitation needs nothing more than a visit to a crafted page (drive-by).
      • Disable VML: Where patching must wait, unregister VML with regsvr32 -u "%CommonProgramFiles%\Microsoft Shared\VGX\vgx.dll" and lock it down with a Deny ACL for Everyone. Check line-of-business app dependencies first.
      • Hunt for compromise: Review EDR history on exposed legacy hosts for child processes of iexplore.exe. On any hit, isolate the host, take a forensic image, and rotate the logged-on user's credentials.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Move legacy IE hosts into a dedicated VLAN with no default route to the internet. Allow outbound HTTP/HTTPS (ports 80/443) only through an authenticating, category-filtering proxy that blocks uncategorised and newly registered domains.
      • Proxy/IPS: Block or alert on external requests carrying IE 6–10 user agents. Enable Suricata/Snort coverage for exploit-kit landing pages and VML exploits (ET EXPLOIT_KIT and CURRENT_EVENTS categories; rules referencing CVE-2013-2551).
      • Endpoint hardening: Use AppLocker/WDAC to block execution from %TEMP% and %APPDATA%. Run IE in Enhanced Protected Mode with hardened zones, disable Active Scripting in the Internet zone, and enforce DEP/ASLR system-wide where possible.
      • Browser consolidation: Remove IE via GPO or Windows Features. If Edge IE mode is required, restrict the site list strictly to the internal URLs that need it.
      • Least privilege: Run users on legacy hosts without local admin rights, so successful code execution does not translate directly into full host takeover.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 1 / EDR process ancestry: Alert when iexplore.exe spawns cmd.exe, powershell.exe, wscript.exe, cscript.exe, rundll32.exe, regsvr32.exe, or mshta.exe. Sigma shape: ParentImage|endswith: '\iexplore.exe' AND Image|endswith: ['\cmd.exe','\powershell.exe','\rundll32.exe'].
      • Sysmon EID 7 / EID 11: Flag iexplore.exe loading vgx.dll, since legitimate VML use is rare today and suspicious. Also flag new .exe/.dll files written by iexplore.exe into %TEMP% or %APPDATA%.
      • Windows Application log, Event ID 1000/1001: An iexplore.exe crash with faulting module vgx.dll is a strong sign of a failed exploit attempt.
      • Proxy logs (SPL): index=proxy http_user_agent="*MSIE 1?.0*" OR http_user_agent="*MSIE [6-9].0*" | stats count by src_ip, dest_host. Correlate with hits on newly registered domains or an application/x-msdownload response shortly after the page load.
      • Zeek/Suricata: In http.log, look for a redirect chain (several 302s across different domains) followed by a binary download to the same client within seconds.

    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

    Use-after-free vulnerability in Microsoft Internet Explorer 6 through 10 allows remote attackers to execute arbitrary code via a crafted web site that triggers access to a deleted object, as demonstrated by VUPEN during a Pwn2Own competition at CanSecWest 2013, aka "Internet Explorer Use After Free Vulnerability," a different vulnerability than CVE-2013-1308 and CVE-2013-1309.

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    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
    microsoftinternet_explorer
    • 7
    • 8
    • 10
    • 9
    • 6
    • —
    • —
    • —
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-416Use After Free

      Variant

      The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

      Entry at MITRE CWE-416

    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

    References & sources

    • docs.microsoft.comMS13-037Vendor advisory, x_refsource_MS, Patch, Vendor advisory
    • us-cert.govTA13-134AThird-party advisory, x_refsource_CERT, Third-party advisory, US government resource
    • twitter.comVUPEN/statuses/309479075385327617x_refsource_MISC, Broken link
    • twitter.comthezdi/statuses/309452625173176320x_refsource_MISC, Not applicable
    • oval.cisecurity.orgoval:org.mitre.oval:def:16317Vulnerability database, signature, x_refsource_OVAL, Broken link
    • h30499.www3.hp.comt5/HP-Security-Research-Blog/Pwn2Own-2013/ba-p/5981157x_refsource_MISC, Broken link, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2013-2551government-resource, US government resource
    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2013-2551
    <a href="https://intel.neosec.eu/en/cve/CVE-2013-2551"><img src="https://intel.neosec.eu/badge/cve/CVE-2013-2551.svg?lang=en" alt="CVE-2013-2551 – NEOSEC Intel" height="20"></a>