CVE-2021-30762: Apple iOS WebKit Use-After-Free Vulnerability

CVE-2021-30762 is a use-after-free vulnerability in Apple iOS WebKit that can lead to code execution when the component processes maliciously crafted web content. It matters because WebKit underpins HTML parsing in Apple Safari and can also appear in other products that rely on WebKit, so a successful exploit may allow an attacker to run code in the context of the affected process on devices that encounter untrusted web material.

CISA notes that the flaw leads to code execution via crafted web content and advises applying updates per vendor instructions. Ransomware use is not documented for this CVE. Confirm all version, configuration, and patch details directly against the Apple advisory before acting.

How it works

This issue is classified as CWE-416 (use-after-free). In a use-after-free condition, memory that has already been freed is later referenced again. If an attacker can influence the timing and content of that reuse—here, through maliciously crafted web content processed by WebKit—the dangling reference can be turned into unintended behavior, including arbitrary code execution inside the vulnerable process.

At a high level, the attacker needs the target to process the crafted content (for example, by loading a page or resource that exercises the vulnerable WebKit path). No further exploit mechanics, proof-of-concept details, or specific trigger sequences are provided in the available facts; treat any public write-ups as unverified until matched against the vendor advisory. The same WebKit code path can affect HTML parsers beyond Safari, so non-Apple products that embed WebKit for HTML processing may also be in scope depending on how they are built and updated.

Am I affected? How to find it in your systems

The vulnerability is reported against Apple iOS WebKit. In practice this surfaces on iOS devices that use WebKit-based browsing or HTML rendering, and potentially on other platforms or applications that incorporate WebKit for parsing web content. Inventory should therefore cover:

• Managed and unmanaged Apple iOS devices (phones and tablets) that browse the web or render HTML from untrusted sources.
• Any enterprise or third-party applications known to embed WebKit or a WebKit-derived HTML engine; confirm embedding and version lineage with the application vendor.
• MDM/EMM or asset-management inventories that record iOS version and installed browser or WebView components.

Because exact affected version ranges are not supplied in the facts, compare every inventoried iOS build and every WebKit-dependent product against the current Apple security advisory for CVE-2021-30762. Look for devices that have not yet received the vendor update named in that advisory.

Telemetry signs of exploitation are not detailed in the provided facts. In general for this class, review device and proxy logs for unexpected process crashes in WebKit-related components, anomalous web-content loads immediately preceding instability, or post-exploitation indicators such as unexpected outbound connections from browser or WebView processes. Absence of such signals does not prove safety; prioritize version compliance over detection alone.

How to remediate

Patch first. Apply the updates Apple has issued for this vulnerability, following the vendor instructions referenced by CISA. Use your MDM or standard iOS update process to drive timely installation across the fleet, and verify that devices report the fixed build once the advisory’s update has been applied.

After patching, harden the surrounding environment for this weakness class:

• Keep iOS and any WebKit-embedding applications on a supported, regularly updated release cadence.
• Restrict unnecessary web-content rendering in high-risk contexts (for example, limit in-app WebViews that load arbitrary URLs).
• Enforce least-privilege browsing profiles and separate high-risk browsing from sensitive corporate data where feasible.
• Re-inventory after the rollout to confirm no residual unpatched devices or third-party WebKit consumers remain.

Confirm the precise update identifiers and any prerequisite steps solely from the Apple advisory; do not rely on secondary summaries.

If you can't patch immediately

When immediate patching is blocked, reduce exposure with compensating controls while you schedule the vendor update:

• Network segmentation and egress filtering: limit devices that still lack the fix from reaching untrusted web content, or force browsing through inspected proxies.
• Virtual patching / WAF or secure web gateway rules: block or detonate known malicious web content patterns that target browser engines; tune rules cautiously because signatures for this specific CVE are not supplied here.
• Feature reduction: disable or restrict in-app HTML rendering, preview panes, or automatic loading of remote web content on unpatched devices where business needs allow.
• Heightened monitoring: alert on WebKit process crashes, unexpected code-injection symptoms, or anomalous network behavior originating from browser processes on still-vulnerable endpoints.
• User guidance: instruct holders of unpatched devices to avoid unsolicited links and untrusted sites until the update is installed.

These measures only lower risk; they do not eliminate the use-after-free condition. Return to full remediation as soon as the vendor update can be applied.

If your data may have been exposed

Actively exploited vulnerabilities can lead to device compromise and subsequent data exposure. If you have reason to believe crafted web content reached unpatched systems, follow your incident-response process: isolate affected devices, preserve logs, credential-reset where appropriate, and assess what data the compromised process could access. Ransomware use is not documented for this CVE, but that does not rule out other post-exploitation activity. As a simple additional check, users can run a free exposure scan of their email addresses against known breach data sets to see whether their credentials have appeared in prior unrelated breaches and then take matching password-hygiene steps.