Threats / Apple / CVE-2021-1871
CVE-2021-1871
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Apple iOS, iPadOS, and macOS vulnerability
WebKit logic vulnerability in Apple iOS, iPadOS, and macOS allows remote code execution through malicious HTML content, affecting Safari and other WebKit-dependent applications.
Verdict
Today item — known-exploited.
A remote attacker can execute arbitrary code by crafting malicious HTML that exploits a logic flaw in WebKit's parsing. The vulnerability has been observed in active exploitation and affects multiple Apple platforms and third-party products using WebKit.
CISA KEV Yes · 2021-11-034EPSS 0.0712 (verify live)5CVSS 9.8 (CISA)3CISA SSVC Exploitation: active · Automatable: yes · Impact: total3
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
2 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).
Probability (EPSS)
EPSS 0.0712 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Apple, iOS, iPadOS, and macOS. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-1173 CWE-1173.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 215 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
WeaknessCWE-1173 · CWE-1173
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious HTML document designed to trigger the WebKit logic flaw during parsing.
Business
User devices become vectors for code execution without user awareness of the attack mechanism.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I deliver the HTML payload through web browsing, email, or embedded content in applications that parse HTML.
Business
Attack surface expands across Safari, mail clients, and third-party apps relying on WebKit rendering.
3
Lateral reach — past segmentation narrative 3
Attacker
I achieve code execution in the context of the vulnerable application or browser process.
Business
Attacker gains ability to access user data, install malware, or pivot to system-level compromise.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05