CVE-2021-30851Public exploitNetwork attack vector

Code execution via unlocked JIT thunk lookup

Published Aug 24, 2021 · Updated Aug 3, 2024

Memory corruption in WebKit before Safari 15, iOS 15, iPadOS 15, tvOS 15, or watchOS 8 allows remote attackers to execute code. An unlocked lookup in FTL::Thunks::keyForSlowPathCallThunk can race a background JIT hash-table rehash, reading freed backing memory. Exploitation requires crafted web content and user interaction to win the timing-dependent race; no sandbox escape or system-level execution is established.

CVSS severity8.8
High
EPSS probability2.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in WebKit before Safari 15, iOS 15, iPadOS 15, tvOS 15, or watchOS 8 allows remote attackers to execute code. An unlocked lookup in FTL::Thunks::keyForSlowPathCallThunk can race a background JIT hash-table rehash, reading freed backing memory. Exploitation requires crafted web content and user interaction to win the timing-dependent race; no sandbox escape or system-level execution is established.

The record

CVE
CVE-2021-30851
Published
Aug 24, 2021
Updated
Aug 3, 2024
Vendor
Apple
Product
iOS and iPadOS
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <15

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · iOS and iPadOSversion=unspecified <15
Apple · Safariversion=unspecified <15
Apple · tvOSversion=unspecified <15
Apple · watchOSversion=unspecified <8

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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