CVE-2026-84554

Executive Summary

CVE-2026-84554 is an integer overflow (CWE-190) in Apple macOS that was addressed through improved input validation and is fixed in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. An attacker who occupies a privileged network position can trigger the flaw to cause a denial-of-service condition on the affected host, yielding an availability-only impact. With a CVSS base score of 5.9 (Medium) and no public proof-of-concept, exploit code, or CISA KEV listing, the immediate exploitation risk is limited but the flaw is network-reachable and requires no user interaction.

Technical Analysis

The core defect is an integer overflow (CWE-190). Per the NVD description, the issue "was addressed with improved input validation," indicating that a value derived from external input was not properly bounded before being used in an arithmetic or memory-sizing operation. When an attacker supplies input that crosses the integer boundary, the resulting value wraps, potentially producing a smaller-than-expected allocation, length, or index. This class of defect classically leads to memory corruption, out-of-bounds access, or a crash — here the disclosed impact is strictly a denial-of-service (availability only), consistent with a fault/crash outcome rather than a demonstrated code-execution primitive.

Key characteristics and constraints drawn strictly from the provided data:

• Attack vector: Network (AV:N). The vulnerable surface is reachable over the network rather than requiring local access.
• Attack complexity: High (AC:H). Successful triggering depends on conditions an attacker cannot fully control, consistent with the need to occupy a "privileged network position" — i.e., a man-in-the-middle or on-path vantage point rather than a trivial unauthenticated remote request.
• Privileges required: None (PR:N). No authentication on the target is needed.
• User interaction: None (UI:N). The victim does not need to perform an action for the flaw to be reachable in the described scenario.
• Scope: Unchanged (S:U). Any impact is confined to the vulnerable macOS component.
• Impact: Availability High (A:H); Confidentiality and Integrity None (C:N/I:N).

Because the NVD description does not name the affected subsystem, function, protocol, or file path, and because the CNA title is empty, this report deliberately avoids attributing the flaw to any specific macOS daemon, service, kernel component, or API. The vulnerability must be understood at the class level: an input-driven integer overflow in a network-exposed macOS code path that terminates in a denial-of-service. The trigger surface — whatever subsystem accepts the unvalidated input — is only reachable when the attacker can position themselves on the network path, which is what raises attack complexity to High.

The "improved input validation" fix implies the pre-patch code trusted or insufficiently checked a length, count, or offset field prior to a size computation. Post-patch macOS versions (Golden Gate 27, Sequoia 15.8, Tahoe 26.7) add the missing bounds/overflow checks. Note the patch-confidence caveat: the fix is CLAIMED by a single source (NVD) and has not been independently corroborated, so version mapping should be verified against Apple's own security release notes before relying on it operationally.

Exploitation Scenarios

No public PoC, exploit code, or Nuclei template exists for this CVE. The chain below is inferred from the vulnerability class (network-reachable integer overflow causing DoS) and the constraints in the NVD description, not from published exploit code.

1. Reconnaissance / target identification. The attacker identifies macOS hosts on a network segment they can influence or intercept. Because AV:N with a required privileged network position, the attacker first establishes on-path placement — e.g., a controlled network segment, an adversary-in-the-middle position, or a compromised upstream node — that lets them influence traffic or input destined for the target.

2. Triggering the flaw class. The attacker crafts network input containing an oversized or boundary-crossing numeric value (a length, count, or offset) that reaches the vulnerable parsing/processing routine. Because input validation pre-patch is insufficient, the value is used in an integer arithmetic operation that overflows and wraps, producing an inconsistent value downstream.

3. Execution method at the class level. No specific payload is defined by the available data. At the vulnerability-class level, the malformed input causes the affected macOS component to mishandle the wrapped value — for example, a size or index derived from the overflow becomes inconsistent — culminating in a fault that terminates or hangs the component. Successful delivery depends on the High-complexity network conditions described in the CVSS vector.

4. Post-exploitation impact. The outcome is a denial-of-service affecting availability of the targeted macOS host or component. There is no disclosed confidentiality or integrity impact and no evidence of code execution, persistence, or lateral movement stemming from this CVE.

Impact Assessment

• Confidentiality: None (C:N). No data exposure is described.
• Integrity: None (I:N). No data modification is described.
• Availability: High (A:H). The flaw can render a macOS component or host unavailable.
• CVSS base: 5.9 (Medium) — driven by the availability impact and network reachability, moderated by High attack complexity.

Blast radius. Impact is confined to the vulnerable macOS system (Scope: Unchanged). The attacker needs no credentials and no user action, but does need a privileged network position, which narrows the practical threat to on-path attackers, hostile networks, or environments where an adversary already controls a network device. Unpatched macOS installations at Golden Gate 27, Sequoia 15.8, and Tahoe 26.7 baselines or earlier are the exposed population; the precise vulnerable range is not enumerated in the provided data.

Business impact. For enterprise fleets, a reliable DoS condition can disrupt end-user productivity, interrupt workloads on macOS endpoints, and — if the affected subsystem is critical — degrade availability of dependent services. Because there is no in-the-wild exploitation evidence, no KEV listing, and no public exploit, current business risk is assessed as moderate and primarily reliability-driven rather than an active-threat emergency.

Detection Guidance

The rules below are vulnerability-class detections for integer-overflow-driven macOS denial-of-service patterns. Because the NVD description names no service, port, protocol, or file path, detections are written generically and should be tuned to the specific macOS subsystem once Apple's advisory identifies it.

Sigma Rule

title: Potential macOS Integer Overflow Denial-of-Service Attempt (CVE-2026-84554)
id: 7b1c9f42-3a55-4d8e-9c11-0a5e84554001
status: experimental
description: Detects crash/DoS patterns on macOS hosts consistent with an integer overflow triggered via malformed network input. Class-level detection.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-84554
author: valtersit.com
date: 2026/01/01
logsource:
  product: macos
  service: crashreport
detection:
  selection_crash:
    EventType: 'Crash'
    Signal|contains:
      - 'SIGSEGV'
      - 'SIGBUS'
      - 'SIGABRT'
  selection_overflow:
    TerminationReason|contains:
      - 'overflow'
      - 'out of bounds'
      - 'bounds'
  filter_known:
    Process|endswith:
      - 'Safari'
      - 'Xcode'
  condition: selection_crash and selection_overflow and not filter_known
falsepositives:
  - Legitimate application crashes involving bounds checks
level: medium

YARA Rule

rule CVE_2026_84554_macOS_int_overflow_dos
{
    meta:
        description = "Class-level hunt for macOS binaries prone to integer-overflow DoS (CVE-2026-84554)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-84554"
        date = "2026-01-01"
        cve = "CVE-2026-84554"

    strings:
        $macho = { CA FE BA BE }
        $macho64 = { CF FA ED FE }
        $cmp1 = "integer overflow" ascii nocase
        $cmp2 = "input validation" ascii nocase
        $cmp3 = "bounds check" ascii nocase

    condition:
        (($macho at 0) or ($macho64 at 0)) and any of ($cmp*)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-84554 macOS integer overflow DoS attempt - abnormal length field"; flow:established; dsize:>1400; byte_test:4,>,0x7FFFFFFF,0,relative; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-dos; reference:cve,2026-84554; sid:8455401; rev:1;)

Elastic Detection

sequence by process.entity_id with maxspan=30s
  [ process where event.type == "start" and process.executable != null ]
  [ process where event.type == "end" and process.exit_code >= 139 ]
  [ file where event.category == "file" and file.name like~ "*.crash" ]

Splunk SPL Query

index=macos OR index=endpoint (sourcetype=macos_crash OR sourcetype=osquery)
| search (signal=SIGSEGV OR signal=SIGBUS OR signal=SIGABRT OR exit_code>=139)
| rex field=TerminationReason "(?<reason>overflow|bounds|out of bounds)"
| stats count values(reason) as reasons by host, process_name
| where count > 3
| sort - count

Wazuh OSSEC Rule

<group name="macos,cve-2026-84554,">
  <rule id="845540" level="7">
    <decoded_as>json</decoded_as>
    <field name="event_type">crash</field>
    <match>SIGSEGV|SIGBUS|SIGABRT|integer overflow|bounds</match>
    <description>CVE-2026-84554: possible macOS integer-overflow denial-of-service event</description>
    <mitre>
      <id>T1499</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 2/4 (CLAIMED — single source claims patch (not independently confirmed)). Version mapping below should be verified against Apple's official security release notes.

1. Immediate mitigations (no patch applied):

   • Restrict the attack precondition: the flaw requires a privileged network position. Harden network segmentation, enforce encrypted and authenticated transport where possible, and monitor for on-path/rogue network devices to deny attackers the vantage point this CVE requires.
   • Treat untrusted networks as hostile — avoid placing macOS hosts (especially unpatched) on flat or unmanaged segments where an on-path attacker could inject malformed input.
   • Apply least-privilege network access controls and egress filtering around macOS endpoints to reduce reach to the vulnerable input surface.

2. Patch / upgrade steps:

   • Upgrade to macOS Golden Gate 27, macOS Sequoia 15.8, or macOS Tahoe 26.7 — the versions listed as fixed in the provided data.
   • Confirm the fix against Apple's own security advisory and release notes before closing the finding, given the CLAIMED (unconfirmed) patch status.
   • Prioritize internet- or untrusted-network-exposed macOS systems during rollout.

3. Long-term hardening:

   • Establish a rapid macOS patch cadence covering all supported OS branches, since this flaw spans multiple release lines.
   • Adopt secure coding practices and code review focused on integer-arithmetic bounds checking (CWE-190), including length/count/offset validation before size computations.
   • Deploy crash telemetry and availability monitoring to detect DoS conditions early.
   • Maintain network-path integrity (802.1X, ARP/DNS integrity monitoring) to deny attackers the on-path position required for exploitation.

References

1. NVD — CVE-2026-84554: https://nvd.nist.gov/vuln/detail/CVE-2026-84554
2. MITRE CWE-190 — Integer Overflow or Wraparound: https://cwe.mitre.org/data/definitions/190.html
3. MITRE ATT&CK T1499 — Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/
4. Apple Security Releases (verify patch for Golden Gate 27 / Sequoia 15.8 / Tahoe 26.7): https://support.apple.com/en-us/HT201222
5. FIRST EPSS — score lookup: https://api.first.org/data/v1/epss?cve=CVE-2026-84554

Threat-actor / exploitation status: No CISA KEV listing, no public proof-of-concept, no Nuclei template, and no exploit code were identified in the provided intelligence. EPSS is 0.00394 (≈33.1st percentile), indicating a low but non-trivial predicted exploitation probability. No known threat-actor campaigns are associated with this CVE in the available data.