TheGreatSageEqualToHeaven/READ.md

## READ.md

      
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    Write-up

A warning to Roblox developers about a powerful exploit primitive. In this, I will detail the research I’ve conducted into this attack vector and walk you through how you as a developer, can protect against exploits with primitives like this.
DataStoreService lets you store data that needs to persist between sessions, such as items in a player’s inventory or skill points. Data stores are consistent per experience, so any place in an experience can access and change the same data, including places on different servers.
By default, experiences tested in Studio cannot access data stores, so you must first enable API services. You will need to do this to test the vulnerabilities.
The idea I wanted to explore when pondering the above question was; can we exploit remotes to prevent data from saving? It is easy to blame the developer for not protecting themselves against such a simple exploit but it ends up being more complicated than that. I found plenty of examples of these vulnerabilities occurring in many popular games such as "Adopt Me!", "Jailbreak", "RoCitizens" and many other games.
The reason such an exploit becomes extremely powerful is because of different types of a game's economy design. Some games may not be affected by such a vulnerability and other games might. An RPG could have a boss that you can only fight once per day per player and it could have a chance to drop a rare in-game item, the vulnerability would allow an exploiter to constantly rollback their data and attempt to get the item again. A great example is "Adopt Me!" where the game has a very stable economy due to the effort put in place to prevent exploits, the game economy could become compromised due to a wide-spread duplication exploit using a rollback.
(All code examples are pseudo-code)

- SetAsync & UpdateAsync

We can use Roblox Studio to test a number of interesting vulnerabilities on a Data store and look for results.
The most simple and easy to patch method of abusing this primitive is using an Instance or userdata and causing it to rollback the player's data. When buying an item the player could choose a color from a color-picker, the developer would add this item with its color to the player's data without thinking too much of it. An exploiter would be able to abuse the remote to add an Instance to the player's data and when the game would attempt to save the Data store would throw an error preventing the game from saving data.
Example:

BuyItem:InvokeServer("Painting", {
	["Name"] = "Mona Lisa",
	["Color"] = workspace --// Was originally Color3.fromRgb(x,y,z)
})
Example 2:

UpdateCanvas:FireServer(
	"Image", 
	workspace --// Originally a number
)
Patch:

if type(input) ~= "type you need here" then 
   return
end
--// Remote code below
PLEASE READ!

I have made a feature request on the devforum that will provide a proper patch to this problem mentioned in this github gist, aside from ones related to size limitations, json injection and developer-made serializers. Having to rely on such unorthodox fixes that are barely documented is incredibly unintuitive especially for new developers or any developer that was simply in the dark about this, any kind of string patterns used for only allowing ascii characters will block international input. This forces developers to use utf8.len as the only fast way to check if a string can be saved, but is still incredible hard to use when you have to iterate tables to verify strings.
Feature request
Example:

ChangePetName:FireServer({
	PetId = 1,
	PetName = "\255" --// Originally a string
})
Example 2.a:

ChangeBillboard:InvokeServer(workspace.MyHouse, "\255")
ChangeBillboard:InvokeServer(workspace.MyHouse, "\237\190\140")
Patch:

utf8.len can be used used as a reliable check for malformed utf-8 strings that cannot be saved.
A lesser known but less efficient vulnerability that is easy to patch is sending a string of bytes bigger than 4mb. This vulnerability is rather uncommon because most developers have proper checks on string length to prevent any type of abuse.
Example:

ChangePosterText:FireServer(workspace.MyHouse.Poster, string.rep([[Shortened: https://paste.sh/djllCQti#ATiNGN82igXDVc81ZvWjFyz4]], 10000))
Example 2:

SavePlaylist:FireServer({
	Playlist_Songs = {19252353,19252511,19295932},
	Playlist_Name = string.rep([[Shortened: https://paste.sh/djllCQti#ATiNGN82igXDVc81ZvWjFyz4]], 10000)
})
Patch:

if #input > 20 then 
   return
end
--// Remote code below
- Obscure vulnerabilities

Some Roblox games serialize and deserialize data in different ways which can lead to weird issues. One example is changing how tables are serialized and deserialized to support ProfileService, I am not sure on why exactly this is done on some games but the issue can be exploited using NaN.
Example Serializer and Deserializer:

--// Serializer
local Data = Player.Data
local ProfileData = Profile.Data
for i,v in Data do 
    ProfileData[v] = i
end

--// Deserializer
local ProfileData = Profile.Data
local Data = Player.Data
for i,v in ProfileData do 
    Data[v] = i
end 
We can abuse this simple serializer by making an unprotected settings remote send 0/0 which will cause an error when serializing. A similar vulnerability can be caused by passing nil instead but that is extremely uncommon.
Example:

ChangeSetting:FireServer("ViewDistance", 0/0)
Patch:

if n ~= n then 
    return
end
--// Remote code below
A much more dangerous vulnerability can occur when using JSON. An exploiter could attempt a JSON injection attack, although less common and dangerous than an SQL injection. I wont be covering JSON injection attacks in this but you can read an article on them.
Article: https://www.comparitech.com/net-admin/json-injection-guide/

An extremely uncommon vulnerability that I had only encountered in one game was setting data to nil so UpdateAsync would cancel the write operation. I doubt this will ever happen in any game that stores more than one string of data.
Example:

ChangeSkill:FireServer(nil)
Patch:

if input == nil then   
    return
end
--// Remote code below
- SAMPLES

print("\\255", pcall(function()
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", "\255")
end))

print("\\237\\190\\140", pcall(function()
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", "\237\190\140")
end))

print("Instance", pcall(function()
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", workspace)
end))

print("4mb limit", pcall(function()
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", string.rep([[
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]], 10000))
end))

print("NaN", pcall(function()
	local data = {[0/0]=true} -- this is the line that errors
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", data)
end))

print("Nil", pcall(function()
	local data = {[nil]=true} -- this is the line that errors
	game:GetService("DataStoreService"):GetDataStore("Test"):SetAsync("Test", data)
end))

print("Update", pcall(function()
	local data = {["ExamplePlayer"] = nil}
	game:GetService("DataStoreService"):GetDataStore("Test"):UpdateAsync("Test", function()
		return data["ExamplePlayer"]
	end)
end))