← Vulnerability feed

Vulnerability record · CVE-2021-1871 · published 2 April 2021

CVE-2021-1871: Apple WebKit logic flaw allows remote code execution

Apple · Ipados

A logic issue in Apple's WebKit was addressed with improved restrictions. It affects macOS Big Sur, Catalina, Mojave, iOS and iPadOS, and a remote attacker may be able to cause arbitrary code execution. Apple stated it was aware of a report that the issue may have been actively exploited.

9.8 CVSS 3.1 Critical CISA KEV since 3 Nov 2021 EPSS 7.0% · top 6.1%
9.8CVSS 3.1 base score, v2 7.5
7.0%EPSS exploitation probability, 30 days
YesIn CISA KEV, fix deadline passed
6Affected product versions listed by NVD
9References
17 Jun 2026Last modified by NVD

Description

A logic issue was addressed with improved restrictions. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, iOS 14.4 and iPadOS 14.4. A remote attacker may be able to cause arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 17 September 2026. Confidence: high.

critical priorityCVSS 9.8 with no authentication or user interaction, confirmed active exploitation per Apple, and inclusion in CISA KEV.

What it is

A logic issue in Apple's WebKit was addressed with improved restrictions. It affects macOS Big Sur, Catalina, Mojave, iOS and iPadOS, and a remote attacker may be able to cause arbitrary code execution. Apple stated it was aware of a report that the issue may have been actively exploited.

Impact

An attacker can execute arbitrary code on the target device, giving full compromise of confidentiality, integrity and availability. No privileges or user interaction are required per the CVSS vector.

Attack surface

Reachable over the network (AV:N) with no authentication (PR:N) and no user interaction (UI:N), consistent with a remotely triggerable WebKit flaw. The record does not specify the exact delivery vector beyond the network.

Exploitation

Listed in CISA KEV with a due date of 2021-11-17, and Apple stated the issue may have been actively exploited. EPSS 30-day probability is 0.07002 (93.8th percentile).

What to do

  • Apply the vendor updates: macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, iOS 14.4 and iPadOS 14.4.
  • Apply the Debian DSA-4923 and Fedora package updates for affected WebKit builds.
  • Track KEV remediation deadlines and confirm all managed Apple devices are on fixed versions.
  • Where patching is delayed, restrict untrusted web content and browsing on affected devices.

Detection

  • Hunt for exploitation attempts against WebKit processes on unpatched macOS, iOS and iPadOS endpoints.
  • Monitor for unexpected code execution or process spawning from browser and WebKit processes.
  • Verify patch state of Apple devices against the fixed versions and flag stragglers.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Exploitation in the wild

CISA added CVE-2021-1871 to the Known Exploited Vulnerabilities catalog on 3 November 2021 as "Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability". Required action: Apply updates per vendor instructions. Federal deadline 17 November 2021.

Affected products

6 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3L6ZZOU5JS7E3RFYGLP7UF Broken LinkMailing List
https://support.apple.com/en-us/HT212146 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212147 Release NotesVendor Advisory
https://www.debian.org/security/2021/dsa-4923 Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3L6ZZOU5JS7E3RFYGLP7UF Broken LinkMailing List
https://support.apple.com/en-us/HT212146 Release NotesVendor Advisory
https://support.apple.com/en-us/HT212147 Release NotesVendor Advisory
https://www.debian.org/security/2021/dsa-4923 Mailing ListThird Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-1871 US Government Resource

Track CVE-2021-1871 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2025-43300Apple iOS, iPadOS and macOS out-of-bounds write via malicious imageAn out-of-bounds write in Apple iOS, iPadOS and macOS is triggered when processing a malicious image file, causing memory corruption. Apple states th…KEVEPSS 22%analysed10.0CVE-2025-32433Erlang/OTP SSH server missing authentication allows remote code executionErlang/OTP SSH servers before OTP-27.3.3, OTP-26.2.5.11 and OTP-25.3.2.20 mishandle SSH protocol messages, letting an unauthenticated attacker execut…KEVEPSS 99%analysed10.0CVE-2025-24201Apple WebKit out-of-bounds write allows sandbox escapeCVE-2025-24201 is an out-of-bounds write in Apple's WebKit that was addressed with improved checks. Maliciously crafted web content may break out of …KEVEPSS 3.8%analysed10.0CVE-2025-24085Apple iOS, iPadOS, macOS, tvOS, visionOS, watchOS Use-After-Free Privilege EscalationA use-after-free flaw in Apple's operating systems was fixed through improved memory management in iOS 18.3, iPadOS 18.3 and 17.7.6, macOS Sequoia 15…KEVEPSS 18%analysed10.0CVE-2021-44228Apache Log4j2 JNDI lookup remote code executionApache Log4j2 versions 2.0-beta9 through 2.15.0 (excluding 2.12.2, 2.12.3, and 2.3.1) do not protect against attacker-controlled LDAP and other JNDI …KEVEPSS 100%analysed9.8CVE-2026-65400Apple macOS Screen Sharing authentication bypassAn improper authentication flaw in Apple macOS Screen Sharing allows a network attacker to authenticate without valid credentials. Apple fixed it via…KEVEPSS 1.2%analysed9.8CVE-2026-24061GNU Inetutils telnetd argument injection allows remote auth bypasstelnetd in GNU Inetutils through 2.7 fails to sanitize the USER environment variable, so a value such as "-f root" is passed as an argument to login …KEVEPSS 99%analysed9.8CVE-2025-39682Linux kernel TLS zero-length record handling flaw on rx_listThe Linux kernel TLS receive path mishandles zero-length records that arrive from the rx_list, breaking the assumption that a record type change cann…KEVEPSS 2.9%analysed

Source: NIST National Vulnerability Database (record CVE-2021-1871), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.