CriticalCVE-2016-3351

    Microsoft Internet Explorer and Edge Information Disclosure Vulnerability (CVE-2016-3351)

    Published In CISA KEV since Sources: CVE.org

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    What is affected, what to do

    Microsoft Internet Explorer 9 through 11 and Microsoft Edge allow remote attackers to obtain sensitive information via a crafted web site, aka "Microsoft Browser Information Disclosure Vulnerability."

    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 9..9
    • Microsoft Internet Explorer 11 eq 10..10
    • Microsoft Internet Explorer 11 eq 11..11

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

    Metrics

    6.5

    Priority

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

    Source: NVD, CVSS v3

    6.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org

    26.5 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 98.0

    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
    234.35 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.

    Read in glossary
    6.5 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
    6.5
    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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    26.5 %
    Elevated — model estimates 10-50% exploitation likelihood.
    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
    98.0
    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: partial
    Source: CISA Vulnrichment, as of 23 June 2022

    Response and mitigation

    Why act now?

    Prioritisation rationale

    On its own this is an information-disclosure flaw. However, it is network-reachable without authentication and needs nothing more than a visit to a crafted page. Malvertising campaigns and exploit kits used it to check for security products, analysis tools or virtualisation before delivering the real payload, which let them evade sandboxes and researchers. CISA flags it as used in ransomware campaigns, and it sits among the CVEs with very high exploitation likelihood. If your estate has no live IE or legacy Edge usage, the risk is low and documenting their retirement is sufficient. Where legacy hosts still browse the internet with IE (common in OT, medical devices or line-of-business apps), treat it as high priority, because those hosts are almost certainly exposed to the code-execution bugs this vulnerability is used to tee up.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every endpoint where Internet Explorer 9–11 or legacy Edge (EdgeHTML) can still be launched. Use software inventory and MDM/Intune queries for mshtml.dll / edgehtml.dll file versions, or iexplore.exe / MicrosoftEdge.exe executions in EDR telemetry. Hosts this far behind are usually missing many later browser fixes too.
      • Patch: Microsoft fixed the issue in the September 2016 cumulative security updates for Internet Explorer and Edge (bulletins MS16-104 / MS16-105). On supported systems, deploy the current Windows cumulative update, which supersedes them. Look up the exact KB per OS in the vendor advisory.
      • Retire legacy browsers: Disable IE11 as a standalone browser via the GPO "Disable Internet Explorer 11 as a standalone browser" or the IE disablement update. Legacy Edge is end-of-life; replace it with Chromium-based Microsoft Edge.
      • Isolate unpatchable assets: Move out-of-support hosts (Windows 7/8.1, embedded, OT HMIs relying on IE) into a dedicated segment. Block general web browsing for them at the proxy.
      • Compromise assessment: For hosts with sustained IE browsing, review proxy logs for exploit-kit and malvertising patterns (see Detection rules). This bug is typically the reconnaissance step before a code-execution exploit.

    2. Runbook step 2

      Mitigation layers

      • Configuration / browser hardening: Make Chromium Edge the default browser. Allow IE mode only through a centrally managed Enterprise Mode Site List for explicitly required internal apps (InternetExplorerIntegrationLevel + InternetExplorerIntegrationSiteList). Disable redirection of incompatible sites to IE.
      • Network / proxy: Block, or at minimum alert on, external requests carrying Trident/ or MSIE user agents. Apply category filtering for ad networks, newly registered domains and uncategorised sites, since delivery is predominantly via malvertising.
      • IPS / web gateway: Enable Suricata/ET exploit-kit landing-page and browser-fingerprinting signatures. In particular, catch scripts that probe for local files via res:// resource requests or mhtml: constructs, typically checking for AV or analysis tooling or VM drivers.
      • Endpoint hardening: Enforce Enhanced Protected Mode and Protected Mode for all zones. Disable ActiveX in the Internet zone. Turn on Microsoft Defender ASR rules restricting child processes, to slow down follow-on stages.
      • IAM / least privilege: Browse only with standard-user rights. Admin accounts get no internet access (tiering, PAWs). This limits the blast radius of the second-stage exploit.

    3. Runbook step 3

      Detection rules

      • Web proxy logs: Look for external requests with IE user agents (MSIE 9.0, MSIE 10.0, Trident/7.0) that coincide with ad-redirect chains (multiple 302s through ad domains). Example in SPL: index=proxy http_user_agent="*Trident/*" | stats dc(dest_host) by src_ip | where 'dc(dest_host)'>50.
      • Sysmon EID 1 / Security 4688: Flag iexplore.exe or MicrosoftEdgeCP.exe as parent spawning powershell.exe, cmd.exe, wscript.exe, mshta.exe, rundll32.exe or regsvr32.exe. Sigma shape: ParentImage|endswith: '\iexplore.exe' combined with Image|endswith from that list. A hit indicates the stage that follows fingerprinting.
      • Sysmon EID 11 / EDR file events: Watch for executables (.exe, .dll, .scr) written to INetCache or %TEMP% by a browser process and executed shortly afterwards.
      • Zeek/Suricata: Watch for heavily obfuscated JavaScript, or payloads hidden steganographically in PNG/GIF responses from ad domains. Also flag short-lived domains followed by application/octet-stream downloads.
      • Inventory check (preventive): This Defender for Endpoint KQL finds remaining legacy browsers: DeviceProcessEvents | where FileName in~ ("iexplore.exe","MicrosoftEdge.exe") | summarize count() by DeviceName.

    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

    Microsoft Internet Explorer 9 through 11 and Microsoft Edge allow remote attackers to obtain sensitive information via a crafted web site, aka "Microsoft Browser Information Disclosure Vulnerability."

    Source: CISA KEV Catalog, cvelistv5, NVD (NIST), 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
    microsoftedge
    • —
    • —
    microsoftinternet_explorer
    • 9
    • 10
    • 11
    • —
    • —
    • —

    Vendors and products

    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

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