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PatchSiren cyber security CVE debrief

CVE-2016-4721 Apple CVE debrief

CVE-2016-4721 is a Medium-severity Apple vulnerability in the IDS - Connectivity component that could let a man-in-the-middle attacker spoof calls using a "switch caller" notification. According to NVD, the issue affects iOS before 10.1 and macOS before 10.12.1. Apple’s vendor advisories and the NVD record indicate this is an integrity-impacting flaw rather than a code-execution issue, but it can still undermine trust in caller identity and call-handling workflows.

Vendor
Apple
Product
Unknown
CVSS
MEDIUM 5.9
CISA KEV
Not listed in stored evidence
Original CVE published
2017-02-20
Original CVE updated
2026-05-13
Advisory published
2017-02-20
Advisory updated
2026-05-13

Who should care

Anyone running affected Apple devices, especially organizations that rely on caller identity, call routing, or voice-based verification on iOS or macOS. Security teams should prioritize devices that remained on iOS versions before 10.1 or macOS versions before 10.12.1 at the time of exposure.

Technical summary

NVD describes the weakness as a network-reachable issue with high attack complexity and no privileges required, where a man-in-the-middle attacker could influence the IDS - Connectivity path enough to trigger or abuse a "switch caller" notification and spoof a call. The recorded CVSS vector is CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N, and NVD maps the weakness to CWE-254.

Defensive priority

Medium. The flaw is limited to integrity impact and requires a man-in-the-middle position, but it affects caller identity signaling on widely deployed Apple platforms and was patched in OS updates.

Recommended defensive actions

  • Upgrade iOS devices to version 10.1 or later.
  • Upgrade macOS systems to version 10.12.1 or later.
  • Verify fleet compliance for any devices that may still be on pre-patch Apple operating system versions.
  • Review business processes that rely on call identity indicators so they do not depend on unverified caller display alone.
  • Use Apple vendor advisories and the NVD record to confirm affected versions and remediation status.

Evidence notes

The description, affected versions, and CVSS vector are taken from the NVD record for CVE-2016-4721. The record lists iOS before 10.1 and macOS before 10.12.1 as vulnerable and cites Apple vendor advisories HT207271 and HT207275. A SecurityFocus BID reference is also present in the source corpus. No unsupported exploit steps or unverified technical details are included.

Sources and references

Verified primary and authoritative sources

  • CVE-2016-4721 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2016-4721

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2016-4721 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2016-4721

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.