Attacker Value

Unknown

CVE-2021-21404

CVE ID

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Attacker Value

Unknown

(0 users assessed)

Exploitability

Unknown

(0 users assessed)

User Interaction

CVE-2021-21404

Disclosure Date: April 06, 2021 •

(Last updated October 07, 2023) ▾

CVE-2021-21404 CVSS v3 Base Score: 7.5

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Add MITRE ATT&CK tactics and techniques that apply to this CVE.

MITRE ATT&CK

Select the MITRE ATT&CK Tactics that apply to this CVE

Collection

Select any Techniques used:

Data from Local System

Data from Removable Media

Data from Network Shared Drive

Input Capture

Input Capture: Keylogging

Input Capture: GUI Input Capture

Input Capture: Web Portal Capture

Input Capture: Credential API Hooking

Data Staged

Data Staged: Local Data Staging

Data Staged: Remote Data Staging

Screen Capture

Email Collection

Email Collection: Local Email Collection

Email Collection: Remote Email Collection

Email Collection: Email Forwarding Rule

Clipboard Data

Automated Collection

Audio Capture

Video Capture

Man in the Browser

Data from Information Repositories

Data from Information Repositories: Confluence

Data from Information Repositories: Sharepoint

Data from Cloud Storage Object

Man-in-the-Middle

Man-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay

Archive Collected Data

Archive Collected Data: Archive via Utility

Archive Collected Data: Archive via Library

Archive Collected Data: Archive via Custom Method

Command and Control

Select any Techniques used:

Data Obfuscation

Data Obfuscation: Junk Data

Data Obfuscation: Steganography

Data Obfuscation: Protocol Impersonation

Fallback Channels

Application Layer Protocol

Application Layer Protocol: Web Protocols

Application Layer Protocol: File Transfer Protocols

Application Layer Protocol: Mail Protocols

Application Layer Protocol: DNS

Proxy

Proxy: Internal Proxy

Proxy: External Proxy

Proxy: Multi-hop Proxy

Proxy: Domain Fronting

Communication Through Removable Media

Non-Application Layer Protocol

Web Service

Web Service: Dead Drop Resolver

Web Service: Bidirectional Communication

Web Service: One-Way Communication

Multi-Stage Channels

Ingress Tool Transfer

Data Encoding

Data Encoding: Standard Encoding

Data Encoding: Non-Standard Encoding

Traffic Signaling

Traffic Signaling: Port Knocking

Remote Access Software

Dynamic Resolution

Dynamic Resolution: Fast Flux DNS

Dynamic Resolution: Domain Generation Algorithms

Dynamic Resolution: DNS Calculation

Non-Standard Port

Protocol Tunneling

Encrypted Channel

Encrypted Channel: Symmetric Cryptography

Encrypted Channel: Asymmetric Cryptography

Credential Access

Select any Techniques used:

OS Credential Dumping

OS Credential Dumping: LSASS Memory

OS Credential Dumping: Security Account Manager

OS Credential Dumping: NTDS

OS Credential Dumping: LSA Secrets

OS Credential Dumping: Cached Domain Credentials

OS Credential Dumping: DCSync

OS Credential Dumping: Proc Filesystem

OS Credential Dumping: /etc/passwd and /etc/shadow

Network Sniffing

Input Capture

Input Capture: Keylogging

Input Capture: GUI Input Capture

Input Capture: Web Portal Capture

Input Capture: Credential API Hooking

Brute Force

Brute Force: Password Guessing

Brute Force: Password Cracking

Brute Force: Password Spraying

Brute Force: Credential Stuffing

Two-Factor Authentication Interception

Forced Authentication

Exploitation for Credential Access

Steal Application Access Token

Steal Web Session Cookie

Unsecured Credentials

Unsecured Credentials: Credentials In Files

Unsecured Credentials: Credentials in Registry

Unsecured Credentials: Bash History

Unsecured Credentials: Private Keys

Unsecured Credentials: Cloud Instance Metadata API

Unsecured Credentials: Group Policy Preferences

Credentials from Password Stores

Credentials from Password Stores: Keychain

Credentials from Password Stores: Securityd Memory

Credentials from Password Stores: Credentials from Web Browsers

Modify Authentication Process

Modify Authentication Process: Domain Controller Authentication

Modify Authentication Process: Password Filter DLL

Modify Authentication Process: Pluggable Authentication Modules

Man-in-the-Middle

Man-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay

Steal or Forge Kerberos Tickets

Steal or Forge Kerberos Tickets: Golden Ticket

Steal or Forge Kerberos Tickets: Silver Ticket

Steal or Forge Kerberos Tickets: Kerberoasting

Defense Evasion

Select any Techniques used:

Direct Volume Access

Rootkit

Obfuscated Files or Information

Obfuscated Files or Information: Binary Padding

Obfuscated Files or Information: Software Packing

Obfuscated Files or Information: Steganography

Obfuscated Files or Information: Compile After Delivery

Obfuscated Files or Information: Indicator Removal from Tools

Masquerading

Masquerading: Invalid Code Signature

Masquerading: Right-to-Left Override

Masquerading: Rename System Utilities

Masquerading: Masquerade Task or Service

Masquerading: Match Legitimate Name or Location

Masquerading: Space after Filename

Process Injection

Process Injection: Dynamic-link Library Injection

Process Injection: Portable Executable Injection

Process Injection: Thread Execution Hijacking

Process Injection: Asynchronous Procedure Call

Process Injection: Thread Local Storage

Process Injection: Ptrace System Calls

Process Injection: Proc Memory

Process Injection: Extra Window Memory Injection

Process Injection: Process Hollowing

Process Injection: Process Doppelgänging

Process Injection: VDSO Hijacking

Indicator Removal on Host

Indicator Removal on Host: Clear Windows Event Logs

Indicator Removal on Host: Clear Linux or Mac System Logs

Indicator Removal on Host: Clear Command History

Indicator Removal on Host: File Deletion

Indicator Removal on Host: Network Share Connection Removal

Indicator Removal on Host: Timestomp

Valid Accounts

Valid Accounts: Default Accounts

Valid Accounts: Domain Accounts

Valid Accounts: Local Accounts

Valid Accounts: Cloud Accounts

Modify Registry

Trusted Developer Utilities Proxy Execution

Trusted Developer Utilities Proxy Execution: MSBuild

Access Token Manipulation

Access Token Manipulation: Token Impersonation/Theft

Access Token Manipulation: Create Process with Token

Access Token Manipulation: Make and Impersonate Token

Access Token Manipulation: Parent PID Spoofing

Access Token Manipulation: SID-History Injection

Deobfuscate/Decode Files or Information

BITS Jobs

Indirect Command Execution

Traffic Signaling

Traffic Signaling: Port Knocking

Rogue Domain Controller

Exploitation for Defense Evasion

Signed Script Proxy Execution

Signed Script Proxy Execution: PubPrn

Signed Binary Proxy Execution

Signed Binary Proxy Execution: Compiled HTML File

Signed Binary Proxy Execution: Control Panel

Signed Binary Proxy Execution: CMSTP

Signed Binary Proxy Execution: InstallUtil

Signed Binary Proxy Execution: Mshta

Signed Binary Proxy Execution: Msiexec

Signed Binary Proxy Execution: Odbcconf

Signed Binary Proxy Execution: Regsvcs/Regasm

Signed Binary Proxy Execution: Regsvr32

Signed Binary Proxy Execution: Rundll32

XSL Script Processing

Template Injection

File and Directory Permissions Modification

File and Directory Permissions Modification: Windows File and Directory Permissions Modification

File and Directory Permissions Modification: Linux and Mac File and Directory Permissions Modification

Execution Guardrails

Execution Guardrails: Environmental Keying

Group Policy Modification

Virtualization/Sandbox Evasion

Virtualization/Sandbox Evasion: System Checks

Virtualization/Sandbox Evasion: User Activity Based Checks

Virtualization/Sandbox Evasion: Time Based Evasion

Unused/Unsupported Cloud Regions

Pre-OS Boot

Pre-OS Boot: System Firmware

Pre-OS Boot: Component Firmware

Pre-OS Boot: Bootkit

Abuse Elevation Control Mechanism

Abuse Elevation Control Mechanism: Setuid and Setgid

Abuse Elevation Control Mechanism: Bypass User Access Control

Abuse Elevation Control Mechanism: Sudo and Sudo Caching

Abuse Elevation Control Mechanism: Elevated Execution with Prompt

Use Alternate Authentication Material

Use Alternate Authentication Material: Application Access Token

Use Alternate Authentication Material: Pass the Hash

Use Alternate Authentication Material: Pass the Ticket

Use Alternate Authentication Material: Web Session Cookie

Subvert Trust Controls

Subvert Trust Controls: Gatekeeper Bypass

Subvert Trust Controls: Code Signing

Subvert Trust Controls: SIP and Trust Provider Hijacking

Subvert Trust Controls: Install Root Certificate

Modify Authentication Process

Modify Authentication Process: Domain Controller Authentication

Modify Authentication Process: Password Filter DLL

Modify Authentication Process: Pluggable Authentication Modules

Impair Defenses

Impair Defenses: Disable or Modify Tools

Impair Defenses: Disable Windows Event Logging

Impair Defenses: HISTCONTROL

Impair Defenses: Disable or Modify System Firewall

Impair Defenses: Indicator Blocking

Impair Defenses: Disable or Modify Cloud Firewall

Hide Artifacts

Hide Artifacts: Hidden Files and Directories

Hide Artifacts: Hidden Users

Hide Artifacts: Hidden Window

Hide Artifacts: NTFS File Attributes

Hide Artifacts: Hidden File System

Hide Artifacts: Run Virtual Instance

Hijack Execution Flow

Hijack Execution Flow: DLL Search Order Hijacking

Hijack Execution Flow: DLL Side-Loading

Hijack Execution Flow: Dylib Hijacking

Hijack Execution Flow: Executable Installer File Permissions Weakness

Hijack Execution Flow: LD_PRELOAD

Hijack Execution Flow: Path Interception by PATH Environment Variable

Hijack Execution Flow: Path Interception by Search Order Hijacking

Hijack Execution Flow: Path Interception by Unquoted Path

Hijack Execution Flow: Services File Permissions Weakness

Hijack Execution Flow: Services Registry Permissions Weakness

Hijack Execution Flow: COR_PROFILER

Modify Cloud Compute Infrastructure

Modify Cloud Compute Infrastructure: Create Snapshot

Modify Cloud Compute Infrastructure: Create Cloud Instance

Modify Cloud Compute Infrastructure: Delete Cloud Instance

Modify Cloud Compute Infrastructure: Revert Cloud Instance

Discovery

Select any Techniques used:

System Service Discovery

Application Window Discovery

Query Registry

System Network Configuration Discovery

Remote System Discovery

System Owner/User Discovery

Network Sniffing

Network Service Scanning

System Network Connections Discovery

Process Discovery

Permission Groups Discovery

Permission Groups Discovery: Local Groups

Permission Groups Discovery: Domain Groups

Permission Groups Discovery: Cloud Groups

System Information Discovery

File and Directory Discovery

Account Discovery

Account Discovery: Local Account

Account Discovery: Domain Account

Account Discovery: Email Account

Account Discovery: Cloud Account

Peripheral Device Discovery

System Time Discovery

Network Share Discovery

Password Policy Discovery

Browser Bookmark Discovery

Domain Trust Discovery

Virtualization/Sandbox Evasion

Virtualization/Sandbox Evasion: System Checks

Virtualization/Sandbox Evasion: User Activity Based Checks

Virtualization/Sandbox Evasion: Time Based Evasion

Software Discovery

Software Discovery: Security Software Discovery

Cloud Service Discovery

Cloud Service Dashboard

Execution

Select any Techniques used:

Windows Management Instrumentation

Scheduled Task/Job

Scheduled Task/Job: At (Linux)

Scheduled Task/Job: At (Windows)

Scheduled Task/Job: Cron

Scheduled Task/Job: Launchd

Scheduled Task/Job: Scheduled Task

Command and Scripting Interpreter

Command and Scripting Interpreter: PowerShell

Command and Scripting Interpreter: AppleScript

Command and Scripting Interpreter: Windows Command Shell

Command and Scripting Interpreter: Unix Shell

Command and Scripting Interpreter: Visual Basic

Command and Scripting Interpreter: Python

Command and Scripting Interpreter: JavaScript/JScript

Software Deployment Tools

Native API

Shared Modules

Exploitation for Client Execution

User Execution

User Execution: Malicious Link

User Execution: Malicious File

Inter-Process Communication

Inter-Process Communication: Component Object Model

Inter-Process Communication: Dynamic Data Exchange

System Services

System Services: Launchctl

System Services: Service Execution

Exfiltration

Select any Techniques used:

Exfiltration Over Other Network Medium

Exfiltration Over Other Network Medium: Exfiltration Over Bluetooth

Automated Exfiltration

Scheduled Transfer

Data Transfer Size Limits

Exfiltration Over C2 Channel

Exfiltration Over Alternative Protocol

Exfiltration Over Alternative Protocol: Exfiltration Over Symmetric Encrypted Non-C2 Protocol

Exfiltration Over Alternative Protocol: Exfiltration Over Asymmetric Encrypted Non-C2 Protocol

Exfiltration Over Alternative Protocol: Exfiltration Over Unencrypted/Obfuscated Non-C2 Protocol

Exfiltration Over Physical Medium

Exfiltration Over Physical Medium: Exfiltration over USB

Transfer Data to Cloud Account

Exfiltration Over Web Service

Exfiltration Over Web Service: Exfiltration to Code Repository

Exfiltration Over Web Service: Exfiltration to Cloud Storage

Impact

Select any Techniques used:

Data Destruction

Data Encrypted for Impact

Service Stop

Inhibit System Recovery

Defacement

Defacement: Internal Defacement

Defacement: External Defacement

Firmware Corruption

Resource Hijacking

Network Denial of Service

Network Denial of Service: Direct Network Flood

Network Denial of Service: Reflection Amplification

Endpoint Denial of Service

Endpoint Denial of Service: OS Exhaustion Flood

Endpoint Denial of Service: Service Exhaustion Flood

Endpoint Denial of Service: Application Exhaustion Flood

Endpoint Denial of Service: Application or System Exploitation

System Shutdown/Reboot

Account Access Removal

Disk Wipe

Disk Wipe: Disk Content Wipe

Disk Wipe: Disk Structure Wipe

Data Manipulation

Data Manipulation: Stored Data Manipulation

Data Manipulation: Transmitted Data Manipulation

Data Manipulation: Runtime Data Manipulation

Initial Access

Select any Techniques used:

Valid Accounts

Valid Accounts: Default Accounts

Valid Accounts: Domain Accounts

Valid Accounts: Local Accounts

Valid Accounts: Cloud Accounts

Replication Through Removable Media

External Remote Services

Drive-by Compromise

Exploit Public-Facing Application

Supply Chain Compromise

Supply Chain Compromise: Compromise Software Dependencies and Development Tools

Supply Chain Compromise: Compromise Software Supply Chain

Supply Chain Compromise: Compromise Hardware Supply Chain

Trusted Relationship

Hardware Additions

Phishing

Phishing: Spearphishing Attachment

Phishing: Spearphishing Link

Phishing: Spearphishing via Service

Lateral Movement

Select any Techniques used:

Remote Services

Remote Services: Remote Desktop Protocol

Remote Services: SMB/Windows Admin Shares

Remote Services: Distributed Component Object Model

Remote Services: SSH

Remote Services: VNC

Remote Services: Windows Remote Management

Software Deployment Tools

Taint Shared Content

Replication Through Removable Media

Exploitation of Remote Services

Internal Spearphishing

Use Alternate Authentication Material

Use Alternate Authentication Material: Application Access Token

Use Alternate Authentication Material: Pass the Hash

Use Alternate Authentication Material: Pass the Ticket

Use Alternate Authentication Material: Web Session Cookie

Remote Service Session Hijacking

Remote Service Session Hijacking: SSH Hijacking

Remote Service Session Hijacking: RDP Hijacking

Lateral Tool Transfer

Persistence

Select any Techniques used:

Boot or Logon Initialization Scripts

Boot or Logon Initialization Scripts: Logon Script (Windows)

Boot or Logon Initialization Scripts: Logon Script (Mac)

Boot or Logon Initialization Scripts: Network Logon Script

Boot or Logon Initialization Scripts: Rc.common

Boot or Logon Initialization Scripts: Startup Items

Scheduled Task/Job

Scheduled Task/Job: At (Linux)

Scheduled Task/Job: At (Windows)

Scheduled Task/Job: Cron

Scheduled Task/Job: Launchd

Scheduled Task/Job: Scheduled Task

Valid Accounts

Valid Accounts: Default Accounts

Valid Accounts: Domain Accounts

Valid Accounts: Local Accounts

Valid Accounts: Cloud Accounts

Account Manipulation

Account Manipulation: Additional Azure Service Principal Credentials

Account Manipulation: Exchange Email Delegate Permissions

Account Manipulation: Add Office 365 Global Administrator Role

Account Manipulation: SSH Authorized Keys

External Remote Services

Create Account

Create Account: Local Account

Create Account: Domain Account

Create Account: Cloud Account

Office Application Startup

Office Application Startup: Office Template Macros

Office Application Startup: Office Test

Office Application Startup: Outlook Forms

Office Application Startup: Outlook Home Page

Office Application Startup: Outlook Rules

Office Application Startup: Add-ins

Browser Extensions

BITS Jobs

Traffic Signaling

Traffic Signaling: Port Knocking

Server Software Component

Server Software Component: SQL Stored Procedures

Server Software Component: Transport Agent

Server Software Component: Web Shell

Implant Container Image

Pre-OS Boot

Pre-OS Boot: System Firmware

Pre-OS Boot: Component Firmware

Pre-OS Boot: Bootkit

Create or Modify System Process

Create or Modify System Process: Launch Agent

Create or Modify System Process: Systemd Service

Create or Modify System Process: Windows Service

Create or Modify System Process: Launch Daemon

Event Triggered Execution

Event Triggered Execution: Change Default File Association

Event Triggered Execution: Screensaver

Event Triggered Execution: Windows Management Instrumentation Event Subscription

Event Triggered Execution: .bash_profile and .bashrc

Event Triggered Execution: Trap

Event Triggered Execution: LC_LOAD_DYLIB Addition

Event Triggered Execution: Netsh Helper DLL

Event Triggered Execution: Accessibility Features

Event Triggered Execution: AppCert DLLs

Event Triggered Execution: AppInit DLLs

Event Triggered Execution: Application Shimming

Event Triggered Execution: Image File Execution Options Injection

Event Triggered Execution: PowerShell Profile

Event Triggered Execution: Emond

Event Triggered Execution: Component Object Model Hijacking

Boot or Logon Autostart Execution

Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder

Boot or Logon Autostart Execution: Authentication Package

Boot or Logon Autostart Execution: Time Providers

Boot or Logon Autostart Execution: Winlogon Helper DLL

Boot or Logon Autostart Execution: Security Support Provider

Boot or Logon Autostart Execution: Kernel Modules and Extensions

Boot or Logon Autostart Execution: Re-opened Applications

Boot or Logon Autostart Execution: LSASS Driver

Boot or Logon Autostart Execution: Shortcut Modification

Boot or Logon Autostart Execution: Port Monitors

Boot or Logon Autostart Execution: Plist Modification

Compromise Client Software Binary

Hijack Execution Flow

Hijack Execution Flow: DLL Search Order Hijacking

Hijack Execution Flow: DLL Side-Loading

Hijack Execution Flow: Dylib Hijacking

Hijack Execution Flow: Executable Installer File Permissions Weakness

Hijack Execution Flow: LD_PRELOAD

Hijack Execution Flow: Path Interception by PATH Environment Variable

Hijack Execution Flow: Path Interception by Search Order Hijacking

Hijack Execution Flow: Path Interception by Unquoted Path

Hijack Execution Flow: Services File Permissions Weakness

Hijack Execution Flow: Services Registry Permissions Weakness

Hijack Execution Flow: COR_PROFILER

Privilege Escalation

Select any Techniques used:

Boot or Logon Initialization Scripts

Boot or Logon Initialization Scripts: Logon Script (Windows)

Boot or Logon Initialization Scripts: Logon Script (Mac)

Boot or Logon Initialization Scripts: Network Logon Script

Boot or Logon Initialization Scripts: Rc.common

Boot or Logon Initialization Scripts: Startup Items

Scheduled Task/Job

Scheduled Task/Job: At (Linux)

Scheduled Task/Job: At (Windows)

Scheduled Task/Job: Cron

Scheduled Task/Job: Launchd

Scheduled Task/Job: Scheduled Task

Process Injection

Process Injection: Dynamic-link Library Injection

Process Injection: Portable Executable Injection

Process Injection: Thread Execution Hijacking

Process Injection: Asynchronous Procedure Call

Process Injection: Thread Local Storage

Process Injection: Ptrace System Calls

Process Injection: Proc Memory

Process Injection: Extra Window Memory Injection

Process Injection: Process Hollowing

Process Injection: Process Doppelgänging

Process Injection: VDSO Hijacking

Exploitation for Privilege Escalation

Valid Accounts

Valid Accounts: Default Accounts

Valid Accounts: Domain Accounts

Valid Accounts: Local Accounts

Valid Accounts: Cloud Accounts

Access Token Manipulation

Access Token Manipulation: Token Impersonation/Theft

Access Token Manipulation: Create Process with Token

Access Token Manipulation: Make and Impersonate Token

Access Token Manipulation: Parent PID Spoofing

Access Token Manipulation: SID-History Injection

Group Policy Modification

Create or Modify System Process

Create or Modify System Process: Launch Agent

Create or Modify System Process: Systemd Service

Create or Modify System Process: Windows Service

Create or Modify System Process: Launch Daemon

Event Triggered Execution

Event Triggered Execution: Change Default File Association

Event Triggered Execution: Screensaver

Event Triggered Execution: Windows Management Instrumentation Event Subscription

Event Triggered Execution: .bash_profile and .bashrc

Event Triggered Execution: Trap

Event Triggered Execution: LC_LOAD_DYLIB Addition

Event Triggered Execution: Netsh Helper DLL

Event Triggered Execution: Accessibility Features

Event Triggered Execution: AppCert DLLs

Event Triggered Execution: AppInit DLLs

Event Triggered Execution: Application Shimming

Event Triggered Execution: Image File Execution Options Injection

Event Triggered Execution: PowerShell Profile

Event Triggered Execution: Emond

Event Triggered Execution: Component Object Model Hijacking

Boot or Logon Autostart Execution

Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder

Boot or Logon Autostart Execution: Authentication Package

Boot or Logon Autostart Execution: Time Providers

Boot or Logon Autostart Execution: Winlogon Helper DLL

Boot or Logon Autostart Execution: Security Support Provider

Boot or Logon Autostart Execution: Kernel Modules and Extensions

Boot or Logon Autostart Execution: Re-opened Applications

Boot or Logon Autostart Execution: LSASS Driver

Boot or Logon Autostart Execution: Shortcut Modification

Boot or Logon Autostart Execution: Port Monitors

Boot or Logon Autostart Execution: Plist Modification

Abuse Elevation Control Mechanism

Abuse Elevation Control Mechanism: Setuid and Setgid

Abuse Elevation Control Mechanism: Bypass User Access Control

Abuse Elevation Control Mechanism: Sudo and Sudo Caching

Abuse Elevation Control Mechanism: Elevated Execution with Prompt

Hijack Execution Flow

Hijack Execution Flow: DLL Search Order Hijacking

Hijack Execution Flow: DLL Side-Loading

Hijack Execution Flow: Dylib Hijacking

Hijack Execution Flow: Executable Installer File Permissions Weakness

Hijack Execution Flow: LD_PRELOAD

Hijack Execution Flow: Path Interception by PATH Environment Variable

Hijack Execution Flow: Path Interception by Search Order Hijacking

Hijack Execution Flow: Path Interception by Unquoted Path

Hijack Execution Flow: Services File Permissions Weakness

Hijack Execution Flow: Services Registry Permissions Weakness

Hijack Execution Flow: COR_PROFILER

Topic Tags

Select the tags that apply to this CVE (Assessment added tags are disabled and cannot be removed)

What makes this of high-value to an attacker?

Vulnerable in default configuration

Unauthenticated

Observed in ransomware attacks

Observed in nation state sponsored attacks

Gives privileged access

Easy to weaponize

Difficult to patch

Common in enterprise

CISA KEV Listed

What makes this of low-value to an attacker?

Vulnerable in uncommon configuration

Requires user interaction

Requires physical access

Requires elevated access

No useful access

Difficult to weaponize

Authenticated

Description

Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server strelaysrv can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it’s likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.

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Ratings & Analysis
Vulnerability Details

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CVSS V3 Severity and Metrics

Data provided by the National Vulnerability Database (NVD)

Base Score:

7.5 High

Impact Score:

3.6

Exploitability Score:

3.9

Vector:

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector (AV):

Network

Attack Complexity (AC):

Low

Privileges Required (PR):

None

User Interaction (UI):

None

Scope (S):

Unchanged

Confidentiality (C):

None

Integrity (I):

None

Availability (A):

High

General Information

Offensive Application

Unknown

Utility Class

Unknown

Ports

Unknown

Vulnerable Versions

syncthing < 1.15.0

Prerequisites

Unknown

Discovered By

Unknown

PoC Author

Unknown

Metasploit Module

Unknown

Reporter

Unknown

Vendors

syncthing

Products

syncthing

References

Additional Info

Authenticated

Unknown

Exploitable

Unknown

Reliability

Unknown

Stability

Unknown

Available Mitigations

Unknown

Shelf Life

Unknown

Userbase/Installbase

Unknown

Patch Effectiveness

Unknown

Rapid7

Technical Analysis

Report as Exploited in the Wild

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Exploitation personally observed in an environment (client, customer, employer, or personal environment)

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CVE ID

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CVE ID:

Unknown

CVE-2021-21404

Unknown

Unknown

None

None

Network

CVE-2021-21404

Description

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CVSS V3 Severity and Metrics

General Information

Vendors

Products

References

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Advisory

Miscellaneous

Additional Info

Technical Analysis

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