Security readout for executives and security teams
Plain-English summary
This is an Apple iOS web-content flaw that could let an attacker run code after a user processes malicious content. Apple fixed it in iOS 12.5.3 and reported possible active exploitation. CISA also lists it in KEV, so treat unpatched iOS assets as a real business risk.
Executive priority
Prioritize remediation because this combines arbitrary code execution impact with documented exploitation signals. Focus first on older or unmanaged iOS devices that may have missed the 12.5.3 security update.
Technical view
CVE-2021-30666 is a CWE-119 buffer overflow in iOS web-content processing. CVSS 3.1 is 8.8 with network attack vector, low complexity, no privileges, user interaction required, and high confidentiality, integrity, and availability impact. Apple says improved memory handling addressed the issue in iOS 12.5.3.
Likely exposure
Exposure is most likely on iOS devices that have not received the Apple fix in iOS 12.5.3 or applicable vendor guidance. The provided sources do not identify exact affected iOS versions beyond the fixed release.
Exploitation context
Apple reported the issue may have been actively exploited, and CISA lists CVE-2021-30666 in the Known Exploited Vulnerabilities catalog. The provided sources do not describe exploit tooling, targets, campaigns, or scale.
Researcher notes
Evidence supports high severity and exploitation concern, but public details in the provided bundle are limited. Avoid assuming affected version ranges, exploit mechanics, or campaign attribution beyond Apple's advisory and CISA KEV listing.
Mitigation direction
- Apply Apple's fixed iOS release, 12.5.3, where applicable.
- Check Apple guidance for device-specific update availability.
- Prioritize remediation for legacy, unmanaged, or internet-used iOS devices.
- Replace devices that cannot receive vendor-supported security updates.
Validation and detection
- Inventory iOS devices and record current operating system versions.
- Confirm devices are on iOS 12.5.3 or an applicable fixed release.
- Review MDM compliance reports for unmanaged or noncompliant iOS assets.
- Track CISA KEV status in vulnerability management workflows.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-119: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-30666 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://support.apple.com/en-us/HT212341CVE reference · x_refsource_MISC
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30666CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Restriction of Operations within the Bounds of a Memory Buffer
Improper Restriction of Operations within the Bounds of a Memory Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.