CriticalCVE-2021-1789

    Apple Multiple Products Type Confusion Vulnerability (CVE-2021-1789)

    Published In CISA KEV since Sources: Debian, CVE.org, Red Hat

    What is affected, what to do

    A type confusion issue in multiple Apple products allows attackers to process maliciously crafted web content, leading to arbitrary code execution. This vulnerability is actively exploited in the wild and affects macOS Big Sur 11.2, Catalina 10.15.7, Mojave 10.14.6, tvOS 14.4, watchOS 7.3, iOS 14.4, iPadOS 14.4, and Safari 14.0.3. The issue has been addressed with improved state handling. It is crucial to apply the specified security updates to prevent arbitrary code execution.

    The vulnerability is being actively exploited; treat it as a priority. Update Apple iOS and iPadOS to version 14.4, Apple macOS to version 11.2, Apple macOS to version 7.3. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Apple iOS and iPadOS lt *..14.4
    • Apple macOS lt *..11.2
    • Apple macOS lt *..7.3
    • Apple macOS lt *..14.4
    • Apple macOS lt *..14.0
    Fixed in
    • Apple iOS and iPadOS 14.4
    • Apple macOS 11.2
    • Apple macOS 7.3
    • Apple macOS 14.4
    • Apple macOS 14.0

    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: Debian, CVE.org, Red Hat

    14.0 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 96.6

    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
    218.58 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
    14.0 %
    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
    96.6
    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 29 January 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-843

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This web-content flaw is network-reachable without authentication. It only needs a user to open crafted content, and the impact on confidentiality, integrity and availability is high. Browser-engine bugs like this are typically the first link in exploit chains for targeted intrusions, delivered through watering-hole sites or crafted links aimed at the mobile devices of exposed individuals. CISA lists no known ransomware use, but exploitation likelihood is still rated very high. Because the fix has been available for years, every affected device points to a gap in patch and lifecycle management. Score this mainly by how many outdated or unpatchable Apple devices can still reach corporate data.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory via MDM/UEM (Jamf, Intune, Workspace ONE): Identify every Apple device below the fixed builds: iOS/iPadOS < 14.4, macOS Big Sur < 11.2, Catalina and Mojave without Security Update 2021-001, Safari < 14.0.3, tvOS < 14.4, watchOS < 7.3. Note that the CPE list in the context mislabels some entries ("macOS 14.4", "macOS 7.3"). These actually refer to iOS/iPadOS 14.4, tvOS 14.4 and watchOS 7.3.
      • Force the update: Push an MDM update command to at least these versions. Because these builds are long superseded, move devices straight to the current supported release. On Catalina/Mojave, also confirm Safari is at 14.0.3 or later.
      • Quarantine devices that cannot be updated: Mark hardware that cannot receive iOS 14.4 or the listed macOS updates as non-compliant. Use Conditional Access to cut it off from mail, VPN and internal web apps, then start decommissioning.
      • Patch high-exposure users first: Prioritise devices belonging to executives, admins, finance/procurement and externally facing staff (press, sales). Targeted links via messenger or email are the typical delivery vector.
      • Triage suspicious devices: On outdated devices showing anomalies, reset credentials and session tokens (SSO, mail, VPN certificates). Re-admit the device only after a full re-install.

    2. Runbook step 2

      Mitigation layers

      • Compliance policy (IAM/zero trust): Set a minimum OS version in Intune/Entra ID or Jamf. Non-compliant devices then lose access to M365, Google Workspace and internal apps automatically.
      • Web proxy/SWG: Block or isolate (remote browser isolation) outdated WebKit clients by User-Agent, e.g. CPU iPhone OS 14_[0-3], CPU OS 1[0-3]_, and Version/14.0 without the .3 suffix. Block uncategorised and newly registered domains for Apple devices.
      • Key point on iOS: Every iOS browser (Chrome, Firefox and Edge included) runs on WebKit, so switching browsers does not mitigate the issue there. On macOS, Chromium- or Firefox-based browsers do reduce exposure, but Mail, Messages and WKWebView-based apps remain affected.
      • macOS endpoint hardening: Restrict JavaScript in Safari for high-risk users via configuration profile. On supported hardware, also enable Lockdown Mode for those users. Remove local admin rights to make post-renderer privilege escalation harder.
      • Mail/messaging filtering: Apply URL rewriting and sandbox detonation to inbound links. Put extra monitoring on accounts with a history of being targeted.

    3. Runbook step 3

      Detection rules

      • MDM compliance as the primary signal: Run a daily report of devices below the minimum version, e.g. Intune KQL: IntuneDevices | where OS == "iOS" and OSVersion startswith "14." and parse_version(OSVersion) < parse_version("14.4").
      • macOS process ancestry (EDR, Defender for Endpoint): The WebKit renderer never legitimately spawns shells. DeviceProcessEvents | where InitiatingProcessFileName has "com.apple.WebKit.WebContent" | where FileName in~ ("sh","bash","zsh","osascript","curl","python3"). As a Sigma rule: ParentImage|contains: 'WebKit.WebContent' with Image|endswith: ['/sh','/bash','/zsh','/osascript'].
      • Crash telemetry: Look for clusters of com.apple.WebKit.WebContent crash reports (Unified Log, /Library/Logs/DiagnosticReports/, MDM diagnostics) shortly after an external URL was opened. Failed exploit attempts often leave exactly these crashes.
      • Proxy/Zeek logs: Surface outdated User-Agents in http.log/ssl.log or proxy logs, e.g. SPL: index=proxy useragent="*iPhone OS 14_[0-3]*" OR useragent="*Version/14.0 Safari*" | stats count by src_ip, url_domain. Correlate hits with rare or newly registered domains.
      • Follow-on activity: Watch for new macOS persistence (LaunchAgents/LaunchDaemons, ESF ES_EVENT_TYPE_NOTIFY_BTM_LAUNCH_ITEM_ADD) and for mobile devices beaconing to internet hosts outside normal Apple and cloud traffic.

    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

    A type confusion issue was addressed with improved state handling. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, tvOS 14.4, watchOS 7.3, iOS 14.4 and iPadOS 14.4, Safari 14.0.3. Processing maliciously crafted web content may lead to arbitrary code execution.

    Source: Debian Security Advisories, NVD (NIST), cvelistv5, CISA KEV Catalog, redhat_csaf

    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
    AppleiOS and iPadOS
    • < 14.4
    • 14.4
    ApplemacOS
    • < 7.3
    • < 11.2
    • < 14.0
    • < 14.4
    • 7.3
    • 11.2
    • 14.0
    • 14.4
    webkitgtkwebkitgtk
    • < 2.30.6
    • 2.30.6

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianwebkit2gtkbuster
    macOSapplemac_os_x10.14.6
    macOSapplemac_os_x10.15.7
    macOSapplemac_os_x—
    macOSapplemacos—
    Mobileappleiphone_os—
    Otherfedoraprojectfedora32
    Otherfedoraprojectfedora33
    Otherappleipados—
    Otherappletvos—
    Otherapplewatchos—

    Weakness classes (CWE)

    • CWE-843Access of Resource Using Incompatible Type ('Type Confusion')

      Base

      The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

      Entry at MITRE CWE-843

    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

    • support.apple.comen-us/HT212147x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212146x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212148x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212149x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212152x_refsource_MISC, Release notes, Vendor advisory
    • lists.fedoraproject.orgFEDORA-2021-864dc37032Vendor advisory, x_refsource_FEDORA, Broken link, Mailing list
    • lists.fedoraproject.orgFEDORA-2021-619711d709Vendor advisory, x_refsource_FEDORA, Broken link, Mailing list
    • security.gentoo.orgGLSA-202104-03Vendor advisory, x_refsource_GENTOO, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-1789government-resource, US government resource
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