OpSec

A client-side Minecraft mod that provides protection against client fingerprinting, tracking exploits, and other privacy focused features.

This is a passion project built and maintained with AI.

Fake phishing sites and Discord servers has been distributing trojanized builds of OpSec. Only download OpSec from these official sources:

• Modrinth
• GitHub Releases
• CurseForge (updated less frequently)

Builds from anywhere else are not official and may be malicious.

What it does

• Spoof as Vanilla - Set brand name to vanilla and block all mod detections
• Channel Spoofing - Conditionally block mod network channels to prevent detection
• Known-Pack Filtering - Conditionally strip built-in pack identifiers from the configuration handshake
• Isolate Pack Cache - Isolate resource packs per-account to prevent tracking
• Block Local URLs - Block resource pack redirects to local/private addresses
• Bypass Server Pack Requirement - Let the user toggle required server resource pack(s) like client packs
• Strip Mod Shader Overrides - Strip server resource pack shader overrides targeting non-whitelisted mods
• Key Resolution Protection - Protect against key resolution mod detection in any server packet
• Meteor Fix - Disable Meteor Client's flawed key resolution protection
• Mod Whitelist - Automatically or manually exempt mods from protection
• Chat Signing Control - Configure chat message signing behavior
• Account Manager - Switch between Minecraft accounts using session tokens
• Telemetry Blocking - Disable data collection sent to Mojang

If you're interested in servers or plugins that are using tracking related exploits then look in the Hall of Shame.

Configurations

The settings menu is accessible via the OpSec button in the multiplayer server selection menu header or via Mod Menu.

If settings are changed while connected to a server it is recommended to reconnect to the server to ensure changes are applied.

Protection Tab

Whitelist Tab

Miscellaneous Tab

Accounts Tab

Debug Commands

The /opsec command is off by default (enable it in Misc → Debug Command). When enabled, use /opsec in-game to access debug information:

Understanding Alerts

• Key Resolution Exploit Detected: Server is probing your keys
• Resource Pack Fingerprinting Detected: Suspicious resource pack URL detected
• Local URL Scan Detected: Resource pack targeting your local/private address

Feature Details

Spoof as Vanilla

Servers can query your client brand to detect whether you're running a modded client. OpSec provides true vanilla spoofing by blocking all mod key resolutions, network channels, and known-pack identifiers (whilst keeping vanilla ones).

• ON - Appear as an unmodified Minecraft client
• OFF - Appear as a standard Fabric client (default)

Set to OFF by default to allow auto mod whitelisting (whitelist mods with network channels).

Isolate Pack Cache

Based on LiquidBounce

Server-required resource packs could be used to fingerprint client instance across accounts.

https://alaggydev.github.io/posts/cytooxien/

Instead of storing all resource packs in a shared cache (~/.minecraft/downloads/), OpSec creates separate cache directories for each account UUID.

Block Local URLs

Derived from ExploitPreventer by NikOverFlow

Malicious servers can send resource pack URLs that redirect to your local network to probe for local devices and services.

https://alaggydev.github.io/posts/cytooxien/

OpSec checks if a redirect or normal request targets a local address, then blocks the connection.

Bypass Server Pack Requirement

Servers can push required resource packs the client is forced to apply. Declining them or toggling required server resource pack(s) is impossible on vanilla client. And fake accepting them can be detectable via key resolution probing the client's resource pack key response.

Minecraft still accepts and downloads these packs as normal but OpSec lets you toggle the pack textures at the client level. The language file of the server resource pack is preserved because servers can probe translation keys (e.g. via {"translate": "some.pack.key"}) to detect whether the pack is actually applied, and a vanilla client with the pack loaded would resolve those keys to the pack-defined value.

With Opsec installed, server resource pack(s) appears as a normal user-toggleable entry in the resource pack menu so you can flip between stripped and fully-loaded.

Modes:

• MANUAL (default): Required packs apply fully like vanilla on push. Optional packs follow vanilla toggle semantics. The user can still unequip any server pack from the pack menu to strip it while keeping lang loaded.
• ASK: Required packs are stripped on push and a consent overlay prompts [Continue] / [Load Pack For Real].
• ALWAYS ON: All server packs are stripped on push. No overlay. You can still toggle them back.

Strip Mod Shader Overrides

Some mods (e.g. Meteor Client) render their GUI with their own shaders loaded through Minecraft's resource manager. A forced server resource pack can overide the mod's own files to ship shaders under that mod to either blank the mod's GUI, crash the client with malformed shaders, or GPU DoS, which also fingerprints that the mod is installed.

OpSec strips shader overrides under assets/<mod>/shaders/ from server packs for any installed mod that isn't whitelisted, so the resource manager falls back to the mod's own bundled shaders. The rest of the pack still loads, so this keeps working even when a server forces the pack to make Bypass Server Pack Requirement unusable.

Vanilla (minecraft) shaders are never touched, and whitelisting a mod lets the server's shader override through.

Key Resolution Protection

Servers can send translatable text containing keys like key.attack or key.hide_icons in any server packet to probe which keys you have bound or mod UI elements your client can resolve. This can reveal the client's installed mods.

OpSec tracks when translation keys are being resolved during server packet processing and blocks Minecraft from resolving them based on your selected brand mode:

Spoof as Vanilla Behavior

• ON: Blocks all mod keys, returns default keybind values for vanilla keys
• OFF: Allows Fabric API and whitelisted mod keys, blocks everything else

When Fake Default Keybinds is disabled, vanilla keybinds resolve to their actual values.

Examples

Spoofing mod keybinds (Returns raw keys/fallback value instead of keybind values):

[key.meteor-client.open-commands] '.'→'key.meteor-client.open-commands'
[key.meteor-client.open-gui] 'Right Shift'→'key.meteor-client.open-gui'

Spoofing vanilla keybinds with Fake Default Keybinds enabled (Returns default keybinds):

[key.hotbar.6] 'Q'→'6'
[key.hotbar.7] 'E'→'7'
[key.hotbar.8] 'R'→'8'

Meteor Fix

Legacy Meteor client a built-in key protection implementation which can lead to guaranteed detection with the key resolution probing.

The server can use a specially crafted translation key probe with a fallback value, instead of expecting the raw key from a vanilla client, its expecting the fallback value instead. Meteor client echos the raw key back instead of the server probe's fallback value.

When the server uses a sign exploit with fallback value on Meteor Client:

'key.meteor-client.open-gui' 'Right Shift'→'key.meteor-client.open-gui'

What a Vanilla response would actaully be:

'key.meteor-client.open-gui' '⟦FALLBACK⟧'→'⟦FALLBACK⟧'

OpSec's bandaid fix for Meteor is to blacklist the AbstractSignEditScreenMixin Mixin to disable Meteor's broken key resolution protection. Allowing OpSec's protection to take over, which already handle fallbacks correctly to match the Vanilla response.

ExploitPreventer Compatibility

For users that prefers ExploitPreventer's core protection implementation but still need OpSec's additional features, both can be installed alongside each other. Overlapping features are automatically disabled to let EP handle them, note that you would lose OpSec features such as channels spoofing. The following OpSec features are deferred to EP:

• Brand Spoofing
• Channel Spoofing
• Known-Pack Filtering
• Isolate Pack Cache
• Block Local URLs
• Key Resolution Protection
• Mod Whitelist

These settings are grayed out in the config screen but your saved preferences are preserved. If you remove EP later, they restore automatically.

Features that don't overlap remain fully functional: alerts, chat signing, account manager, telemetry blocking, Strip Mod Shader Overrides, and Meteor Fix.

Channel Spoofing

Servers can query your registered network channels to detect which mods you have installed.

OpSec can conditionally block mod channels that are registered with the server to prevent detection. This is enabled by default, its behavior is controlled by the mod whitelist and

Known-Pack Filtering

Servers can probe your mod-injected pack identifiers that certain mods exposes to detect whether you're running a modded client or using certain mods. OpSec intercepts the outgoing ServerboundSelectKnownPacks response and strips entries belonging to non-whitelisted mods. Real vanilla and auto whitelisted packs still pass through.

Spoof as Vanilla Behavior

• ON: Strips all mod-injected packs.
• OFF: Keeps packs for whitelisted mods, strips the rest.

Only active on clients where Fabric's known-packs hook is present (MC 1.21.11+ with modern fabric-api).

Mod Whitelist

Some mods require server communication to function properly (e.g., VoiceChat, Xaero's Minimap quick travel). The whitelist allows you to exempt specific mods from channel spoofing, key resolution protection, known-pack filtering, and shader override stripping.

Modes:

• OFF: All mod content is blocked
• AUTO (default): Mods that register network channels are automatically whitelisted as they are the most likely to have server-side functionalities
• CUSTOM: Manually select which mods to whitelist from the installed mod list

When the whitelist is active (AUTO or CUSTOM), Spoof as Vanilla will be disabled as exposing Fabric mods would need the client brand to match accordingly.

CUSTOM mode lists every installed mod so any mod can be whitelisted; AUTO mode only shows mods that register network channels.

Chat Signing Control

Based on No Chat Reports.

Cryptographic signatures by default are attached to every chat messages. Removing them makes it impossible to track and associate your chat messages with your Minecraft client, and, by extension, Microsoft account.

Modes:

• OFF: Strip all chat signatures, but prevents you from chatting in servers that enforces secure chat.
• Auto: Only sign messages when the server enforces secure chat.
• ON: Default Minecraft behavior, signs every messages.

Account Manager

Based on Meteor Client.

Add Minecraft accounts with session tokens and switch between them without restarting the game.

• Session Token Login - Add accounts using access tokens
• Refresh Token - Fetch new session tokens for expired accounts
• Offline Account - Add username-only accounts without authentication
• Account Switching - Click an account to login, click again to logout to original account
• Token Validation - Refresh to check if tokens are still valid (expired tokens marked red)
• Import/Export - Backup and restore accounts via JSON files

Session tokens expire after some time. Use the Refresh button to check validity.

Telemetry Blocking

From No Chat Reports.

Minecraft collects and sends telemetry data to Mojang, including:

• Game events and player actions
• Performance metrics
• Client configuration
• Usage statistics

OpSec blocks telemetry sending to Mojang when telemetry blocking is enabled. Does not effect gameplay.

References

• ExploitPreventer - Local URL blocking and server key resolution protection anti-measures
• No Chat Reports - Chat signing control and telemetry blocking
• No Prying Eyes - Secure chat enforcement detection
• MixinSquared - Mixin cancellation for Meteor Fix
• Stonecutter - Multi-version build system
• Fabric API - Fabric translation and keybind keys

Disclaimer

OpSec is a privacy tool designed to protect players from unwanted client fingerprinting and tracking. It is not intended or encouraged for use in bypassing server rules, evading bans, or gaining unfair advantages. Users are responsible for complying with the rules and terms of service of any server they connect to.