CriticalCVE-2021-30858

    Apple iOS, iPadOS, macOS Use-After-Free Vulnerability (CVE-2021-30858)

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

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    What is affected, what to do

    A use after free issue was addressed with improved memory management. This issue is fixed in iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6.

    The vulnerability is being actively exploited; treat it as a priority. Update Apple macOS to version 11.6, Apple iOS to version 14.8. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Apple macOS lt *..11.6
    • Apple iOS lt *..14.8
    Fixed in
    • Apple macOS 11.6
    • Apple iOS 14.8

    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, SingCERT

    13.4 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 96.4

    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
    218.41 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 exploitedSource: Apple (CVE.org), CSA/SingCERT How we classify
    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
    13.4 %
    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
    96.4
    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-416

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE is on KEV because Apple itself acknowledged reports of active exploitation. WebKit bugs like this are typically delivered through crafted links or compromised websites to selected high-value individuals, often as the first stage of a spyware chain, rather than in mass campaigns. The flaw is network-reachable without authentication but requires user interaction. Exploitation likelihood is high, and there is no known ransomware use. Organisations with unmanaged or outdated iPhones and iPads among executives or KRITIS operators should treat this as high priority, as should anyone running WebKit-based rendering services on Linux. If the fleet is fully MDM-managed and patched, the remaining work is evidencing compliance.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Enforce patch level via MDM: Update iOS and iPadOS to at least 14.8 and macOS Big Sur to at least 11.6. Legacy iPhones/iPads that cannot run iOS 14 need iOS 12.5.5. Set a minimum OS version as a compliance condition in Jamf, Intune, Kandji or similar, and cut non-compliant devices off from corporate mail, VPN and SSO.
      • Patch WebKitGTK/WPE on Linux: On Debian 10 and 11, upgrade the webkit2gtk and wpewebkit packages (apt update && apt list --upgradable | grep -i webkit). A patch is available from the vendor — look up the exact package version in the Debian Security Advisory. Restart any applications that embed WebKit afterwards.
      • Inventory unpatchable devices: Identify hardware that cannot receive iOS 12.5.5 or 14.8, and Macs running releases older than Big Sur. Retire these devices or move them to an isolated guest network with no access to internal services.
      • Prioritise high-risk users: Update executives, legal, communications and admin staff first. On current hardware, evaluate Lockdown Mode for this group.
      • Find server-side WebKit parsers: Identify services that render untrusted HTML with WebKit, such as headless rendering, PDF or thumbnail generation, and mail preview. Disable them or restrict them to trusted input until they are patched.

    2. Runbook step 2

      Mitigation layers

      • Network/proxy: Route web traffic from managed Apple devices through a secure web gateway with category and reputation filtering. Block newly registered domains, uncategorised destinations and known exploit-kit categories. On iOS, use always-on or per-app VPN with DNS filtering.
      • macOS endpoint hardening: Restrict JavaScript in Safari for high-risk profiles via configuration profile. Enforce Gatekeeper and SIP, and make sure EDR telemetry covers com.apple.WebKit.WebContent. A non-WebKit default browser helps on macOS but not on iOS, where every browser uses WebKit.
      • Isolate Linux services: Run WebKit-based renderers in a container or sandbox with a seccomp profile, a read-only filesystem and an unprivileged user. Allow no outbound internet access beyond explicitly approved destinations.
      • IAM/access control: Tie conditional access to device compliance, including OS version, so a compromised mobile device cannot keep long-lived tokens. Shorten session lifetimes for mobile clients.
      • Mail/messaging: Rewrite inbound email links and analyse them at time of click. Focus phishing awareness on mobile devices, because exploitation requires the user to open malicious content.

    3. Runbook step 3

      Detection rules

      • MDM compliance as a detection source: Run a daily report of devices below iOS/iPadOS 14.8, below Big Sur 11.6, or below 12.5.5 on iOS 12 hardware. Treat every hit as an open finding.
      • macOS EDR process ancestry: Alert on child processes of com.apple.WebKit.WebContent or Safari such as sh, bash, zsh, osascript, curl or python*. Sigma shape: ParentImage|endswith: 'com.apple.WebKit.WebContent' AND Image|endswith: ['/sh','/bash','/zsh','/osascript','/curl'].
      • Crash patterns: Look for clusters of WebContent crash reports (/Library/Logs/DiagnosticReports/com.apple.WebKit.WebContent*.ips) on macOS and in sysdiagnose crash logs on iOS. Repeated crashes after visiting the same URL suggest failed exploitation attempts.
      • Linux auditd: Add -a always,exit -F arch=b64 -S execve -k webkit_child, then flag hits whose parent process is WebKitWebProcess. SPL: index=linux key=webkit_child parent_comm="WebKitWebProcess".
      • Proxy/Zeek: Correlate visits by mobile Apple user agents (Mobile/.* Safari) to rare domains with unusual outbound connections to new IPs or ASNs shortly afterwards. KQL sketch: DeviceNetworkEvents | where InitiatingProcessFileName has "WebContent" and RemoteUrl !in (known_good).

    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 use after free issue was addressed with improved memory management. This issue is fixed in iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.

    Source: Debian Security Advisories, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), cvelistv5, CSA/SingCERT

    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
    • < 14.8
    • 14.8
    ApplemacOS
    • < 11.6
    • 11.6

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux10.0
    Linuxdebiandebian_linux11.0
    Linuxdebianwebkit2gtkbullseye
    Linuxdebianwebkit2gtkbuster
    Linuxdebianwpewebkitbullseye
    macOSapplemacos—
    Mobileappleiphone_os—
    Otherfedoraprojectfedora33
    Otherfedoraprojectfedora34
    Otherappleipados—

    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
    Apple (CVE.org)CVE.org (MITRE) (opens in a new tab)actively exploited
    CSA/SingCERTVulnerabilities in Apple iOS, iPadOS, MacOS and WatchOS (opens in a new tab)CSA/SingCERTactively exploited

    References & sources

    • support.apple.comen-us/HT212804x_refsource_MISC, Third-party advisory
    • support.apple.comen-us/HT212807x_refsource_MISC, Third-party advisory
    • seclists.org20210917 APPLE-SA-2021-09-13-3 macOS Big Sur 11.6Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • seclists.org20210917 APPLE-SA-2021-09-13-1 iOS 14.8 and iPadOS 14.8Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • seclists.org20210917 APPLE-SA-2021-09-13-5 Safari 14.1.2Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • openwall.com[oss-security] 20210920 WebKitGTK and WPE WebKit Security Advisory WSA-2021-0005Mailing list, x_refsource_MLIST, Mailing list
    • lists.fedoraproject.orgFEDORA-2021-c00e45b6c0Vendor advisory, x_refsource_FEDORA, Release notes
    • seclists.org20210921 APPLE-SA-2021-09-20-6 Additional information for APPLE-SA-2021-09-13-1 iOS 14.8 and iPadOS 14.8Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • seclists.org20210921 APPLE-SA-2021-09-20-7 Additional information for APPLE-SA-2021-09-13-3 macOS Big Sur 11.6Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • debian.orgDSA-4975Vendor advisory, x_refsource_DEBIAN, Mailing list, Third-party advisory
    • debian.orgDSA-4976Vendor advisory, x_refsource_DEBIAN, Mailing list, Third-party advisory
    • support.apple.comkb/HT212824x_refsource_CONFIRM, Third-party advisory
    • seclists.org20210924 APPLE-SA-2021-09-23-1 iOS 12.5.5Mailing list, x_refsource_FULLDISC, Mailing list, Third-party advisory
    • lists.fedoraproject.orgFEDORA-2021-edf6957b7dVendor advisory, x_refsource_FEDORA, Release notes
    • openwall.com[oss-security] 20211026 WebKitGTK and WPE WebKit Security Advisory WSA-2021-0006Mailing list, x_refsource_MLIST, Mailing list
    • openwall.com[oss-security] 20211027 Re: WebKitGTK and WPE WebKit Security Advisory WSA-2021-0006Mailing list, x_refsource_MLIST, Mailing list
    • openwall.com[oss-security] 20211027 Re: WebKitGTK and WPE WebKit Security Advisory WSA-2021-0006Mailing list, x_refsource_MLIST, Mailing list
    • openwall.com[oss-security] 20211027 Re: WebKitGTK and WPE WebKit Security Advisory WSA-2021-0006Mailing list, x_refsource_MLIST, Mailing list
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30858government-resource, US government resource
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