CVE-2026-53420

Executive Summary

CVE-2026-53420 is a buffer overflow vulnerability (CWE-120) in a Zoom Phone feature of Zoom Workplace Clients that may allow an unauthenticated network-adjacent attacker to achieve escalation of privilege. Affected systems are deployments of the Zoom Workplace Client software that include the Zoom Phone component. The impact is high, with a CVSS base score of 8.0 reflecting potential compromise of confidentiality, integrity, and availability across a changed security scope.

Technical Analysis

The vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input, commonly referred to as a classic buffer overflow). It resides in a Zoom Phone feature within the Zoom Workplace Clients. According to the NVD description, the flaw may allow an unauthenticated user to conduct an escalation of privilege via network access.

At the vulnerability-class level, a buffer overflow of this type occurs when a program copies input into a fixed-length buffer without validating that the input length does not exceed the buffer's capacity. When oversized or malformed input is processed, adjacent memory is overwritten. In a privilege escalation context, this memory corruption can be leveraged to alter control flow or corrupt security-relevant data structures, potentially allowing the attacker to execute code or operations in a higher-privileged context than intended.

The CVSS vector CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H provides the following analytic picture:

• AV:N (Network) — the vulnerability is reachable over a network, consistent with a Zoom Phone feature that processes network-delivered data.
• AC:H (High) — exploitation requires conditions beyond the attacker's direct control, implying some degree of timing, state, or interaction complexity.
• PR:L (Low) — the attacker requires some low level of privilege or positioned access, though the description states the user may be unauthenticated.
• UI:R (Required) — some form of user interaction is necessary for exploitation.
• S:C (Changed) — a successful exploit can affect resources beyond the vulnerable component's original security scope.
• C:H / I:H / A:H — high impact to confidentiality, integrity, and availability.

Note: The CNA title and affected version ranges were not provided. No public proof-of-concept, exploit code, or Nuclei template exists for this CVE, and the reference field contains insufficient technical detail to identify specific function names, API parameters, or data structures involved in the overflow. Analysis is therefore limited to the vulnerability class and the behavioral characteristics implied by the CVSS vector. No vulnerability has been observed being exploited in the wild.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class and CVSS vector. No specific function names, endpoints, or parameters are asserted because none are disclosed in the source data.

1. Reconnaissance / Target Identification An attacker identifies hosts running the Zoom Workplace Client with the Zoom Phone feature enabled. Because the vulnerable surface is network-reachable (AV:N), the attacker would enumerate exposed Zoom Phone service endpoints, likely by scanning for client-related listening ports or by monitoring collaboration traffic where the Zoom Phone component processes inbound data.

2. Triggering the Flaw Class The attacker crafts network-delivered input targeting the Zoom Phone feature. Per the CWE-120 class, the attacker supplies data whose length exceeds an internal fixed-size buffer that the component fails to bounds-check. Based on UI:R, a user action is likely required to cause the crafted data to be processed (for example, accepting or interacting with a malformed call, message, or session element). Per AC:H, the attacker must satisfy additional preconditions before control-flow corruption is reliably achievable, meaning naive attempts may simply crash the component.

3. Payload / Execution Method At the vulnerability-class level, oversized input overwrites adjacent memory. In a successful escalation, this corruption may be shaped to redirect execution or alter privileged state. The attacker gains escalated privileges relative to the compromised client context (S:C indicates impact beyond the original component scope). No specific offsets, ROP chains, or function pointers are disclosed, and none should be assumed.

4. Post-Exploitation Impact Given C:H/I:H/A:H, successful exploitation can compromise data confidentiality, integrity, and availability. Escalation of privilege on the client could allow the attacker to access protected Zoom Phone data (call metadata, recordings, account context), modify application behavior, or pivot to further resources within the changed scope.

Impact Assessment

The CVSS base score of 8.0 (High) reflects serious risk. The attack vector is Network, meaning exploitation is possible remotely rather than requiring local access. Attack complexity is High, which moderates the likelihood of reliable exploitation but does not eliminate it. Privileges required are Low and user interaction is Required, indicating a targeted attack that likely involves inducing a user to engage with crafted network data. Scope is Changed, so compromise can extend beyond the vulnerable Zoom Phone component into the broader client environment. Confidentiality, integrity, and availability impacts are all High.

Business impact includes potential compromise of the Zoom Workplace Client endpoint, exposure of phone/communication data, and a foothold that could be escalated within a corporate environment that relies on Zoom for voice and collaboration. Blast radius is limited to systems running affected Zoom Workplace Clients with the Zoom Phone feature, but within an enterprise those clients are frequently deployed on user workstations that hold access to other sensitive resources.

Detection Guidance

Sigma Rule

title: Potential Zoom Phone Buffer Overflow Exploitation Attempt
id: 8f3c1a92-7d5e-4b21-9a6f-0c2e6b4d1f77
status: experimental
description: Detects crashes or anomalous termination of Zoom Workplace Client processes that may indicate buffer overflow exploitation (CVE-2026-53420).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-53420
author: valtersit.com
date: 2026-01-01
tags:
  - attack.t1068
  - cve.2026.53420
logsource:
  category: process_creation
  product: windows
detection:
  selection_image:
    Image|endswith:
      - '\Zoom.exe'
      - '\ZoomPhone.exe'
  selection_fault:
    EventID:
      - 1000
      - 1001
  condition: selection_image and selection_fault
falsepositives:
  - Legitimate application crashes unrelated to exploitation
level: medium

YARA Rule

rule CVE_2026_53420_ZoomPhone_BufferOverflow_Indicator
{
    meta:
        description = "Heuristic detection for potential buffer overflow exploitation of Zoom Phone feature in Zoom Workplace Clients (CVE-2026-53420)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-53420"
        date = "2026-01-01"
        cve = "CVE-2026-53420"

    strings:
        $zoom = "Zoom Workplace" ascii wide nocase
        $phone = "ZoomPhone" ascii wide nocase
        $m1 = { 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 }
        $m2 = { 41 41 41 41 41 41 41 41 41 41 41 41 }

    condition:
        ($zoom or $phone) and any of ($m1, $m2)
}

Suricata IDS Rule

alert tcp any any -> $HOME_NET any (msg:"CVE-2026-53420 Potential Zoom Phone Buffer Overflow Exploitation"; flow:to_client,established; content:"|41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41|"; depth:64; threshold:type both, track by_src, count 5, seconds 60; reference:cve,2026-53420; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-53420; classtype:attempted-user; sid:2026534200; rev:1;)

Elastic Detection

process where process.name in ("Zoom.exe", "ZoomPhone.exe") and
  event.action == "process-crashed"

Splunk SPL Query

index=endpoint (Image="*\\Zoom.exe" OR Image="*\\ZoomPhone.exe") (EventCode=1000 OR EventCode=1001)
| stats count by host, Image, EventCode
| where count > 0
| sort - count

Wazuh OSSEC Rule

<group name="zoom,cve-2026-53420,">
  <rule id="100534" level="8">
    <if_sid>61603</if_sid>
    <field name="win.eventdata.image">(?i)Zoom(Phone)?\.exe</field>
    <description>CVE-2026-53420: Zoom Workplace Client process anomaly possibly indicating Zoom Phone buffer overflow exploitation</description>
    <mitre>
      <id>T1068</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected version list is currently available.

1. Immediate mitigations

• Limit network exposure of Zoom Phone features where feasible; restrict inbound network access to Zoom Workplace Clients using network segmentation and firewall policy.
• Advise users to avoid interacting with unsolicited or unexpected calls/session elements originating from untrusted sources, since user interaction (UI:R) is required for exploitation.
• Enable endpoint detection and logging (process crash telemetry, EDR monitoring) for Zoom client processes to catch anomalous termination patterns.
• Monitor vendor channels for an advisory or update specific to CVE-2026-53420.

2. Patch / upgrade steps

• No patch is currently documented. Track the vendor's official security advisory and apply the fixed Zoom Workplace Client release as soon as it is published.
• Maintain a client inventory so affected endpoints can be rapidly updated once a fix is available.

3. Long-term hardening

• Enforce automatic client updates and centralized software inventory management.
• Apply least-privilege principles to endpoint users to reduce the value of any privilege-escalation primitive.
• Adopt memory-safe coding oversight expectations for vendors and require timely coordinated disclosure and patching SLAs.
• Continuously monitor CISA KEV and vendor advisories for updates to this CVE's status.

References

• NVD — CVE-2026-53420: https://nvd.nist.gov/vuln/detail/CVE-2026-53420
• MITRE CWE-120 (Buffer Copy without Checking Size of Input): https://cwe.mitre.org/data/definitions/120.html
• MITRE ATT&CK T1068 — Exploitation for Privilege Escalation: https://attack.mitre.org/techniques/T1068/
• FIRST EPSS (score not yet assigned for this CVE): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog (CVE not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are currently associated with CVE-2026-53420. No public proof-of-concept or exploit code was identified at the time of writing.