CVE-2026-53413

Executive Summary

CVE-2026-53413 is a high-severity memory corruption vulnerability residing in the annotator function of Zoom Clients. The flaw stems from a missing bounds check that permits a buffer over-write, enabling a malicious meeting participant to execute arbitrary code remotely on another participant's device via network access. The vulnerability carries a CVSS score of 8.3, is currently unpatched (patch confidence 0/4), and poses a significant risk to enterprise environments that rely on Zoom for communication. Successful exploitation could lead to full system compromise, data exfiltration, and lateral movement within corporate networks, given that the attack requires user interaction and high attack complexity but no privileges.

Technical Analysis

The NVD description for CVE-2026-53413 identifies a missing bounds check in the annotator function of Zoom Clients. The annotated function is a component responsible for handling real-time annotation overlays—features used during screen sharing and collaborative whiteboarding sessions in meetings. The vulnerability is classified under CWE-787: Out-of-bounds Write, confirming that the flaw allows data to be written past the end of an allocated memory buffer.

Vulnerability Mechanism: The core issue is that the annotator function processes incoming data (likely annotation coordinates, drawing strokes, or shape attributes) without validating the size of the input against the allocated buffer boundary. When a malicious participant sends crafted annotation data that exceeds the expected buffer size, the function writes beyond the buffer's bounds. This buffer over-write can corrupt adjacent memory, including heap metadata, function pointers, or other sensitive data structures.

Attack Surface: The attack surface is the meeting/media channel over which annotation data is transmitted. Zoom clients exchange annotation data in real-time between participants during screen-share annotation sessions. The receiving participant's client parses this data in the annotator function, which is the vulnerable code path. Since the attack vector is network-based (AV:N) and requires no authentication or pre-existing privileges (PR:N), any participant in a meeting—or potentially an unauthenticated attacker who can join a meeting—can trigger the flaw.

Attack Complexity: The vector reports high attack complexity (AC:H), suggesting that successful exploitation likely requires racing conditions, precise heap layout manipulation, or other timing-dependent techniques. This could involve heap spraying to place critical objects at predictable memory addresses or orchestrating the annotation buffer to overlap with function pointers.

User Interaction: The vector requires user interaction (UI:R), meaning the victim must be an active meeting participant. The victim may need to have the annotation feature enabled or be viewing a screen share where annotations are active. This lowers the barrier for a targeted attack, as social engineering can easily persuade a victim to join a malicious meeting.

Peripheral Impact: The CVSS vector reports scope changed (S:C), meaning exploitation can impact resources beyond the vulnerable component's security authority. This indicates that the buffer over-write can be leveraged to escape the Zoom client's process boundary and compromise the underlying operating system or other applications.

Exploitation Scenarios

Reconnaissance/Target Identification: The attacker identifies a target—a known enterprise Zoom user or a specific meeting. The attacker can either create a malicious meeting and lure the victim via phishing, or join an existing public meeting with annotation enabled. Given the unpatched state, the attacker may target high-value individuals (executives, IT admins) whose devices hold elevated access to critical systems.

Triggering the Vulnerable Flaw: Once in the same meeting session, the attacker activates the screen-share annotation feature (or waits for the victim to enable it). The attacker then sends a crafted stream of annotation data—deliberately oversized drawing commands, malformed shape coordinates, or excessive stroke data—that exceeds the buffer capacity allocated by the annotator function on the victim's client. The missing bounds check accepts this data, causing the write operation to overflow the buffer.

Payload/Execution Method (Class-Level): As the buffer over-write occurs, the attacker corrupts adjacent memory. While the exact exploit strategy is not documented in public advisories (no PoC available), class-level technique would involve overwriting a function pointer or return address with a pointer to attacker-controlled data placed in the annotation buffer. The crafted data itself can contain shellcode that, when the corrupted pointer is dereferenced, redirects execution to the shellcode, achieving remote code execution within the victim's Zoom client process. From there, the attacker escalates privileges on the local system.

Post-Exploitation Impact: With code execution on the victim's machine, the attacker can:

• Install persistent backdoors or malware.
• Capture screenshots, keystrokes, and clipboard data.
• Exfiltrate sensitive documents and credentials.
• Use the compromised host as a pivot point for lateral movement into the enterprise network, escalating toward domain controller access (post-exploitation T1078 or T1098).

Inference Note: No public PoC or exploit code is available (PoC status: None). This attack chain is inferred from the NVD description's mention of meeting participants and the buffer over-write vulnerability class. Insufficient technical detail is available to specify exact payload structures or memory offsets.

Impact Assessment

Business Impact: The primary impact is high confidentiality, integrity, and availability impact (C:H/I:H/A:H per CVSS). A successful exploit grants the attacker full control over the victim's Zoom process, which typically runs with the privileges of the logged-in user. In enterprise environments where users operate with local administrative rights, this translates directly to full system compromise.

Affected Systems: All Zoom desktop clients (Windows, macOS, and Linux) are presumed affected, as the annotator function is part of the core client application across platforms. The absence of version-specific data means the entire current Zoom client fleet should be considered vulnerable until patch status is confirmed.

Blast Radius: The vulnerability affects any organization using Zoom for internal or external communications—including webinars, town halls, and client meetings. Given that Zoom is widely deployed, the potential exposure includes financial institutions, healthcare providers, government agencies, and technology companies. The per-interaction compromise (one meeting participant attacking another) means the risk scales with the volume of external meetings an organization conducts.

CISA KEV Status: Not listed in CISA's Known Exploited Vulnerabilities catalog, which means no confirmed in-the-wild exploitation activity has been reported publicly. However, the patch confidence of 0/4 indicates no vendor fix is currently available, leaving the window for exploitation open and increasing the urgency of compensating controls.

Detection Guidance

Sigma Rule

title: Zoom Annotator Buffer Overflow Exploitation Attempt
id: e9f3c1a2-####-####-####-############
status: experimental
description: Detects anomalous Zoom client behavior indicative of CVE-2026-53413 exploitation attempts, specifically abnormal process crashes or memory access violations in the zoom.exe process.
author: Valtersit Threat Intel Team
date: 2026/06/15
logsource:
  category: process_creation
  product: windows
detection:
  selection_crash:
    EventID: 1000  # Application Error
    Image|endswith: '\zoom.exe'
    Application Error|contains:
      - '0xc0000005'  # Access Violation
      - '0xc00000fd'  # Stack Overflow
  selection_wer:
    EventID:
      - 1001  # Windows Error Reporting
      - 1002
    Faulting Application|contains: 'zoom'
  condition: selection_crash or selection_wer
falsepositives:
  - Legitimate Zoom crashes due to graphics driver issues
  - Memory pressure causing out-of-memory errors
level: high

YARA Rule

rule Zoom_Annotator_BufferOverwrite_CVE_2026_53413
{
    meta:
        author = "Valtersit Threat Intel"
        description = "Detects suspicious annotation data patterns or shellcode indicators in Zoom client memory"
        cve = "CVE-2026-53413"
        date = "2026-06-15"
    strings:
        $annot_string = "annotator" ascii wide nocase
        $buffer_write_pattern = { 89 4C 24 ?? 8B 41 }  // Potential mov [rsp+..], ecx; mov eax, [rcx] pattern
        $shellcode_byte = { 90 90 90 90 90 90 }  // NOP sled
        $jmp_esp = { FF E4 }  // JMP ESP
        $call_esp = { FF D4 }  // CALL ESP
    condition:
        uint16(0) == 0x5A4D and  // MZ header if scanning executables
        filesize < 10MB and
        (1 of ($shellcode_byte, $jmp_esp, $call_esp) and $annot_string) or
        ($buffer_write_pattern and $annot_string)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"ZOOM Annotator Buffer Overflow Exploitation Attempt - CVE-2026-53413"; flow:established,to_server; content:"|00 00 00 01|"; depth:4; content:"annotat"; nocase; distance:0; within:256; pcre:"/annotat.{0,4096}(\.\.|%00|FF FF FF FF)/is"; classtype:attempted-user; sid:2026534130; rev:1; metadata:created_at 2026_06_15, updated_at 2026_06_15, cve CVE-2026-53413, severity HIGH;)

Note: This rule looks for anomaly patterns in Zoom meeting traffic—specifically, excessive annotation data sizes or non-standard encoding in annotation frames. The PCRE looks for length-prefix anomalies or oversized payloads relative to annotation data norms.

Elastic Detection

sequence by process.entity_id with maxspan=5m
  [ process where event.type == "start" and process.name == "zoom.exe" ]
  [ process where event.code == "1000" and process.name == "zoom.exe" ]
  [ file where event.type == "creation" and file.name == "*.dmp" and process.name == "werfault.exe" ]

Alternative EQL for crash monitoring:

any where event.dataset == "windows.error" and
    process.name == "zoom.exe" and
    error.code in ("0xc0000005", "0xc00000fd", "0xc0000094")

Splunk SPL Query

index=windows sourcetype=WinEventLog:Application EventCode=1000
| where Image LIKE "%zoom%"
| stats count by Image, Source, Message, _time
| rename Source as Faulting_Module, Message as Error_Details
| fields Image, Source, Message, count

index=windows sourcetype="WinEventLog:System" SourceName="Microsoft-Windows-WER-SystemErrorReporting"
| where Message LIKE "*zoom*"
| bucket _time span=1h
| stats dc(host) as affected_hosts by _time
| sort -affected_hosts

Wazuh OSSEC Rule

<group name="zoom_overflow,">
  <rule id="580836" level="12">
    <if_sid>1105340</if_sid>
    <field name="win.event.system.eventID">1000</field>
    <match>zoom.exe</match>
    <description>Zoom Client crash detected - possible CVE-2026-53413 exploitation attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>local_policy</group>
  </rule>

  <rule id="580837" level="10">
    <decoded_as>windows-event-channel</decoded_as>
    <field name="win.system.channel">Application</field>
    <field name="win.system.providerName">Application Error</field>
    <match>0xc0000005</match>
    <description>Access violation error detected - potential exploit behavior</description>
    <group>local_policy</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Status: No vendor patch is available. Patch confidence is 0/4. No official fix, advisory, or workaround has been released by Zoom for CVE-2026-53413.

Immediate Mitigations:

1. Restrict annotation usage: Disable the screen-share annotation feature via Zoom admin policies until a patch is released. In the Zoom Admin Console, navigate to Account Management → Account Settings → Meeting tab → "Annotation" and disable. Apply to all user groups.
2. Restrict external meetings: Disable external participants from joining internal meetings by default, or restrict annotation to authenticated/trusted domains only.
3. Endpoint protection: Deploy EDR solutions with behavioral detection for memory corruption and exploit-hedging features (e.g., CrowdStrike Falcon's Exploit Protection, Microsoft Defender Exploit Guard). Enable ASLR, DEP, and SEHOP. Consider using Microsoft's Enhanced Mitigation Experience Toolkit or built-in EMET equivalents.
4. Network segmentation: Monitor and restrict outbound Zoom traffic through web proxies to only allow Zoom's official data centers; block other media streams.

Patch/Upgrade Steps:

• Monitor Zoom's official security advisory page (support.zoom.com/hc/en-us/categories/201001986-Security) on a daily basis.
• Subscribe to CISA alerts (cisa.gov) for updates on CVE-2026-53413.
• Apply the vendor patch immediately upon release. Test in a pilot group, then push to all clients via auto-update.
• In the interim, consider using only the Zoom web client (which may not have the same code base) or an alternative platform with a fixed annotation module—only if business-critical meetings require annotation.

Long-Term Hardening:

• Establish a vulnerability management SLA for communication tools; critical client-side issues above CVSS 8.0 should have a 48-hour patching window.
• Implement application allowlisting (e.g., Windows Defender Application Control) to prevent non-whitelisted binaries from executing.
• Run Zoom with a least-privilege account; do not grant local admin rights to users.
• Periodically audit meetings and users for external participants; enforce MFA for Zoom accounts.
• Maintain offline or air-gapped systems for highly confidential communications until the threat is resolved.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-53413 — Official NVD record with description, CVSS scoring, and CWE classification.
2. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — Confirms no in-the-wild exploitation is currently registered for this CVE.
3. Zoom Security Advisory Page: https://support.zoom.us/hc/en-us/security — Monitor this vendor advisory channel for patch announcements and extended technical details.
4. MITRE ATT&CK Technique T1190 (Exploit Public-Facing Application): https://attack.mitre.org/techniques/T1190/ — Reference for the attack chain classification (meeting as exposed application surface).
5. CWE-787 Out-of-bounds Write: https://cwe.mitre.org/data/definitions/787.html — Technical reference for the vulnerability class and exploitation mechanics.

Threat Actor Activity: No publicly known threat actor campaigns have been attributed to CVE-2026-53413 as of the report date. The vulnerability remains unpatched, and no exploit-in-the-wild evidence has been confirmed. Security teams should maintain heightened awareness given the lack of a fix.