CVE-2026-53418

Executive Summary

CVE-2026-53418 is an improper authorization vulnerability (CWE-939) in the handler for a custom URL scheme in Zoom Workplace for Android versions prior to 7.2.1. The flaw allows an unauthenticated, network-positioned actor to trigger a privilege escalation by invoking the affected custom URL scheme handler, which fails to correctly validate authorization before acting on the request. With a CVSS base score of 8.1 (High), successful exploitation compromises both confidentiality and integrity of the affected mobile client, though no public proof-of-concept, exploit code, or in-the-wild activity has been observed at the time of this report.

Technical Analysis

The vulnerability resides in the handler that processes incoming custom URL scheme invocations within Zoom Workplace for Android. Custom URL schemes are the mechanism by which one mobile application — or a web page, or an external link — can hand off a request to another application by using a registered scheme identifier rather than an HTTP(S) URL. When the operating system routes such a URI to the target application, the application's scheme handler parses the URI and performs the action encoded in it (for example, launching a meeting, joining via a deep link, or passing parameters to an internal component).

The root cause, as described in the NVD entry, is improper authorization within that handler. CWE-939 ("Improper Authorization in Handler for Custom URL Scheme") describes exactly this class: the application exposes a custom scheme endpoint but does not correctly verify that the caller is entitled to invoke the functionality the scheme exposes, nor does it correctly constrain what internal actions the URI can trigger. Because custom URL schemes are, by design, reachable from other applications and from web content rendered by a browser on the same device, any authorization weakness in the handler becomes externally reachable without requiring the attacker to compromise the target application first.

The CVSS vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N indicates the following: the attack is network-reachable (AV:N); the attack complexity is low (AC:L) with no special conditions beyond a crafted request; the attacker requires some privileges (PR:L), consistent with an actor controlling an app, a browser session, or a network position that can hand a URI to the victim's device; no user interaction separate from the delivery of the URI is required (UI:N); and the scope is unchanged (S:U), meaning the impact remains within the security authority of the vulnerable component. Confidentiality and integrity impacts are High (C:H/I:H); availability impact is None (A:N), so the vulnerability does not primarily cause denial of service.

An important nuance: although the NVD description labels the actor "unauthenticated," the CVSS vector assigns PR:L (Low privileges). These are reconciled in practice by the fact that the attacker does not hold valid credentials within Zoom's authentication model (hence "unauthenticated" in the textual description), while still requiring a low-privilege foothold on the device or network — for example, control of another app that can issue the scheme URI, or the ability to serve content to a browser on the target device — to actually reach the handler. This report treats the preconditions per the CVSS vector: a low-privilege, network-capable actor able to cause the crafted URI to be processed.

Note that the description does not disclose the exact scheme identifier, the specific internal components reached, the URI parameters abused, or the exact authorization check that is missing. Per the accuracy constraints for this report, no such implementation details are asserted here. The analysis is confined to the vulnerability class and the attack mechanism implied by CWE-939 and the NVD text. Any reference to specific endpoint names, parameter names, or code paths would be speculative and is deliberately omitted. Readers should consult Zoom's own advisory and release notes for the authoritative technical description once available.

Exploitation Scenarios

The attack chain below is described at the vulnerability-class level. No public proof-of-concept exists for CVE-2026-53418, and no exploit code or Nuclei template has been published; the sequence is inferred from the CWE-939 class and the NVD description. It must not be read as a confirmed, tested exploit chain.

1. Reconnaissance and target identification. The attacker identifies a target population running Zoom Workplace for Android below version 7.2.1. Because Android application versions can be fingerprinted through device management telemetry, application inventory data, or by social/technical means, the attacker selects victims whose device can be induced to process a crafted custom URI. The attacker also determines a delivery vector: a malicious or compromised application already installed on the device that can invoke the scheme, a web page that a browser on the device renders, or a network position from which a URI-bearing action can be triggered.

2. Triggering the flaw class. The attacker constructs a URI that targets the Zoom custom URL scheme handler and encodes the action the handler will perform once it processes the request. The defining weakness is improper authorization in that handler: the handler does not adequately verify that the caller is permitted to request the encoded action, nor does it adequately restrict the action the URI can reach. The attacker therefore does not need to authenticate to Zoom; the mere fact that the URI reaches the handler is sufficient to cross the authorization boundary the handler was supposed to enforce.

3. Execution. The crafted URI is delivered to the victim device through the chosen vector and handed to the Zoom Workplace for Android handler. Because the handler fails to enforce authorization correctly, it processes the request and performs the action the attacker encoded, in the security context of the Zoom application rather than in a context constrained to the caller's privileges. This is the escalation-of-privilege step: a low-privilege or external caller causes the application to act with privileges the caller should not have been able to invoke.

4. Post-exploitation impact. Per the CVSS subscores, the attacker can achieve High confidentiality and High integrity impact within the vulnerable component. Concretely, the flaw class permits an unauthorized caller to cause the application to perform privileged actions — potentially accessing data or manipulating application state that should be reserved for authorized, authenticated flows. Availability is not impacted (A:N). Because the scope is unchanged (S:U), the impact is bounded by the security authority the Zoom client itself holds; the vulnerability does not, by itself, imply kernel-level or cross-application compromise beyond what the Zoom application's privileges allow. The PR:L rating indicates the attacker's own starting privilege is low, making this a realistic privilege-escalation primitive for a device-resident or network-adjacent actor.

Impact Assessment

The CVSS base score of 8.1 reflects a High-severity issue. The vector's constituent parts map to business impact as follows:

• AV:N (Network): The attack does not require physical access or local adjacency to the device; a remote or network-delivered URI is sufficient. This widens the attacker population relative to a local-only bug and complicates perimeter-based defenses.
• AC:L (Low complexity): No race conditions, no memory-layout grooming, and no specialized conditions are required. A crafted URI is the core primitive, which lowers the skill barrier and increases the likelihood of replication once details become public.
• PR:L (Low privileges): The attacker needs only a minimal foothold — control of an on-device app that can issue the scheme URI, the ability to serve browser-rendered content to the device, or a network position that can induce URI processing. This is a meaningful but not trivial precondition.
• UI:N (No user interaction): The description implies the flaw can be triggered without a discrete, security-relevant user decision beyond the delivery action itself, reducing reliance on user error.
• S:U (Unchanged scope): Impact is contained to the vulnerable Zoom component's security authority.
• C:H / I:H (High confidentiality and integrity impact): The attacker can potentially read data and alter application state within the Zoom client's authority.
• A:N (No availability impact): No denial of service is expected as a direct result.

Blast radius. The affected asset is the Zoom Workplace for Android mobile client. In an enterprise context, these clients carry meeting content, account tokens, user identity linkage, and often access to organizational directories and meeting metadata. An authorization bypass in the client can therefore expose not just the device owner's data but also organizational data surfaced through the client, and can be used as a stepping stone to abuse trusted client functionality. Because the vulnerability is network-reachable and low-complexity, a fleet of unmanaged or BYOD Android devices running vulnerable Zoom clients represents the largest exposure surface; managed-device fleets with enforced update policies are more readily contained.

Confidence and uncertainty. The impact rating is taken directly from the published CVSS vector. No exploit, PoC, or KEV entry exists, and EPSS has not yet scored this CVE, so no probabilistic exploitation likelihood can be stated. The absence of a published PoC reduces near-term exploitation risk but does not eliminate it, since CWE-939 handler bugs are frequently rediscovered and weaponized after advisory publication.

Detection Guidance

Detection for this class of vulnerability is challenging because the exploitation primitive is a custom URI scheme invocation rather than a network protocol anomaly with a stable signature. The rules below target the observable correlates: anomalous Android intent/URI traffic at the endpoint layer, mobile application artifacts on disk, and any network telemetry that exposes custom-scheme redirection. The following rules are illustrative detection logic for the vulnerability class and should be tuned to the environment; because the exact scheme string and parameters are not disclosed in the source data, operators should substitute the actual Zoom scheme identifiers observed in their environment.

Sigma Rule

title: Suspicious Custom URL Scheme Invocation Targeting Zoom Workplace for Android
id: 7f3c1a2e-5b64-4d9a-9c1e-2a8b6d4f0e11
status: experimental
description: Detects anomalous invocation of the Zoom custom URL scheme via ADB, intent handling, or browser redirection on Android endpoints. Detects the CVE-2026-53418 vulnerability class (improper authorization in custom URL scheme handler). Tune scheme identifiers to the environment.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-53418
author: valtersit.com Threat Intelligence
date: 2026/01/01
tags:
  - attack.privilege_escalation
  - attack.t1068
  - cve.2026-53418
logsource:
  product: android
  service: intent
detection:
  selection_scheme:
    intent_action:
      - 'android.intent.action.VIEW'
    intent_data|contains:
      - 'zoommtg://'
      - 'zoomus://'
  selection_suspicious_origin:
    calling_package|endswith:
      - 'com.android.chrome'
      - 'com.android.vending'
      - 'com.google.android.gms'
  selection_privileged_component:
    target_component|contains:
      - 'com.zipow.videobox'
  condition: selection_scheme and (selection_suspicious_origin or selection_privileged_component)
falsepositives:
  - Legitimate deep links opened by users from email or messaging clients
  - Enterprise MDM push of configured deep links
level: medium

YARA Rule

rule CVE_2026_53418_Zoom_Android_URI_Scheme_Handler
{
    meta:
        description = "Detects Zoom Workplace for Android artifacts consistent with the CVE-2026-53418 improper authorization in custom URL scheme handler vulnerability class. File-level correlation, not exploit detection."
        author = "valtersit.com Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-53418"
        cve = "CVE-2026-53418"
        severity = "high"

    strings:
        $scheme1 = "zoommtg://" ascii wide nocase
        $scheme2 = "zoomus://" ascii wide nocase
        $pkg1    = "com.zipow.videobox" ascii wide nocase
        $act1    = "android.intent.action.VIEW" ascii wide nocase
        $meta    = "versionName" ascii wide nocase

    condition:
        uint32be(0) == 0x504B0304 and
        filesize < 200MB and
        ($pkg1) and
        (
            ($scheme1 or $scheme2) and $act1
        )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-53418 Zoom Workplace Android Custom URL Scheme Authorization Bypass Attempt"; flow:established,to_client; http.header; content:"Location"; nocase; content:"zoommtg://"; nocase; distance:0; pcre:"/zoommtg:\/\/[^\r\n]*(action|join|conf|uid|token)/i"; reference:cve,2026-53418; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-53418; classtype:attempted-privilege-escalation; sid:9002618; rev:1;)

alert http any any -> any any (msg:"CVE-2026-53418 Zoom Workplace Android Custom URL Scheme Redirect Delivery"; flow:established,to_client; http.header; content:"Location"; nocase; content:"zoomus://"; nocase; distance:0; reference:cve,2026-53418; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-53418; classtype:attempted-privilege-escalation; sid:9002619; rev:1;)

Elastic Detection

sequence by host.id with maxspan=5s
  [process where process.name in ("adb", "am", "cmd") and
     process.command_line : ("*zoommtg://*" or "*zoomus://*")]
  [any where
     (process.name == "com.zipow.videobox" or event.category == "intent") and
     (event.action == "intent_invocation" or event.type == "start") and
     wildcard(event.original, "*android.intent.action.VIEW*")]

Splunk SPL Query

index=android_endpoint (sourcetype="android:intent" OR sourcetype="android:logcat")
(uri="*zoommtg://*" OR uri="*zoomus://*" OR intent_data="*zoommtg*" OR intent_data="*zoomus*")
| eval risk_flag=if(match(uri, "(?i)(action|join|conf|uid|token)="), "high", "low")
| where caller_package IN ("com.android.chrome","com.android.vending","com.google.android.gms") OR risk_flag="high"
| stats count min(_time) as first_seen max(_time) as last_seen
        values(caller_package) as callers values(uri) as uris
        by host device_id
| where count > 0
| sort - count
| table first_seen last_seen host device_id count callers uris

Wazuh OSSEC Rule

<group name="cve_2026_53418,zoom_android,">
  <rule id="100618" level="10">
    <if_sid>100000</if_sid>
    <decoded_as>json</decoded_as>
    <field name="uri">zoommtg://</field>
    <description>CVE-2026-53418: Zoom Workplace for Android custom URL scheme invocation detected (privilege escalation class)</description>
    <mitre>
      <id>T1068</id>
    </mitre>
    <group>privilege_escalation,</group>
  </rule>

  <rule id="100619" level="10">
    <if_sid>100000</if_sid>
    <decoded_as>json</decoded_as>
    <field name="uri">zoomus://</field>
    <description>CVE-2026-53418: Suspicious Zoom custom URL scheme invocation detected</description>
    <mitre>
      <id>T1068</id>
    </mitre>
    <group>privilege_escalation,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence is 0/4 — UNPATCHED, meaning no patch evidence has been obtained from any tracked source at the time of writing, and no vendor fix or workaround is recorded in the data provided. The guidance below is therefore organized as defense-in-depth and should be validated against Zoom's own advisory before operational reliance.

1. Immediate mitigations

• Update any Zoom Workplace for Android deployment to version 7.2.1 or later if that build is available. The NVD description names 7.2.1 as the fixed version boundary; treat this as the primary remediation target even though patch provenance could not be independently confirmed in the source data.
• Inventory Android endpoints and identify all clients below 7.2.1. Prioritize unmanaged and BYOD devices, which are least likely to have received an update.
• Use mobile device management (MDM) or enterprise mobility tooling to enforce a minimum application version policy for the Zoom client on managed fleets.
• Reduce the attack surface by restricting which network content and which applications can issue custom-scheme URIs on managed devices, where policy permits. Browser and OS-level controls that require explicit user confirmation before opening external application schemes add a layer of friction to the delivery step.
• Where organizational policy allows, consider temporarily blocking or restricting Zoom client use on devices that cannot be updated, and surface a compensating control such as conditional access to Zoom services from compliant devices only.

2. Patch/upgrade steps

• Verify the current Zoom Workplace for Android version on each device (application settings or MDM inventory).
• Where 7.2.1 or later is obtainable, push the update through the managed application channel and confirm the version post-update.
• Track Zoom's official security bulletin and the CVE-2026-53418 NVD entry for the authoritative fixed-version statement; the version boundary in this report derives from the NVD description and no vendor advisory URL was provided in the source data.
• Re-validate after update that the previously reachable scheme behavior is no longer triggerable, if a safe test method is available, using only authorized internal testing.

3. Long-term hardening

• Maintain continuous mobile application inventory with automatic flagging of versions below known-good baselines, so that future CVEs in this class are detected by version drift rather than by manual audit.
• Adopt a policy of disabling or tightly constraining custom URL scheme reachability for security-sensitive applications on managed Android devices, and require user confirmation for cross-application scheme launches.
• Monitor for the detection correlates described above, and tune the scheme identifiers once Zoom's advisory or observed traffic discloses the actual strings.
• Establish an ongoing review cadence for mobile client advisories, since authorization flaws in custom scheme handlers are a recurring pattern (CWE-939) across mobile collaboration software.

References

• NVD — CVE-2026-53418: https://nvd.nist.gov/vuln/detail/CVE-2026-53418
• MITRE CWE-939 — Improper Authorization in Handler for Custom URL Scheme: https://cwe.mitre.org/data/definitions/939.html
• FIRST EPSS — CVE-2026-53418 (not yet scored at the time of this report): https://api.first.org/data/v1/epss?cve=CVE-2026-53418
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-53418 not listed at the time of this report): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Zoom Trust Center / Security Bulletins (consult for the vendor's authoritative advisory and fixed-version confirmation): https://www.zoom.com/en/trust/security-bulletin/

Threat actor and exploit-in-the-wild evidence: none. No public proof-of-concept, exploit code, or Nuclei template was identified, CVE-2026-53418 is not listed in CISA KEV, and no campaign attribution is available from the provided data.