MarekKnapek

Think of advanced features of WinRAR not being accessible without valid licence key. Ehm, WinRAR distributes the same binary for both licensed and unlicensed users, unlocking the features with license key or with a crack (equivalent of NOPing the if). What if instead WinRAR distributed different binary for each licensed user, advanced features encrypted by per-user key. Crack or keygen would need to use some particular user's binary with theirs license. Easily trackable. Or crack would need need to be applied once and then distribute the un-encrypted features / code.

Think of password protected access to something, anything. Instead of checking if(password == some_constant){...} or if(hash(password) == precomputed_hash){...} you encrypt that something. The first variant has disadvantage that some_constant is stored inside your binary, thus password visible to anybody. The second variant ... the same, hash of the password is stored inside the binary and could be brute-forced or rainbow-tabled. Both variants have the disadvantage, that there is a run-time check refusing access to some data, but those data are available in the binary anyway. Just open the program in debugger or in hex editor and NOP the if out. With my approach the data is unreadable without the correct password. The app could not be convinced / persuaded to provide the data in any way without the password.

This is true in real world also, not only in computer world or programming world. Think of steam engine, it enabled sooo much progress in other fields. Also invention of lathe and precision measuring and engineering. Before that, invention of "simple machines" such as pulley, bolt/screw, windlass, lever. The same in math, physics, chemistry and so on.

Oversimplified:

• You have your current OS, text editor, compiler.
• You write code of the new improved OS using your current OS, text editor.
• You compile the code (text file), compilation yields the new OS or the new kernel (binary file).
• You replace (overwrite) your current kernel by the new kernel (current OS by new OS). This is possible, because while the OS is running it is in RAM not touching the disk.
• You restart.
• BIOS loads the new OS from disk to RAM and executes it.
• tada.wav

More questions:

• How to update BIOS? Answer: The same.
• How the first OS, text editor and compiler were created? Answer: The same. Using more primitive OS, text editor and compiler each step into the past. At the beginning there were toggle switches, punch cards, punch ribbon strips or similar.

The same style of question would be: How to create a hammer if in order to create a hammer you need a hammer? How was the first hammer created? Answer: By more primitive hammer, or something that is no hammer, but almost works as a hammer.

For more info read about bootstrapping compilers. Or trusting the trust by Ken Thompson.

It is trade-off between convenience and security. With my approach stolen cookies are not usable from different computer / IP, the attacker needs additional work, he needs the victim computer to do the harm, his computer cannot do any harm. The downside is the user needs another log-in in case of his external IP changes. How often is it? Switch between mobile/WiFi. Otherwise ... almost never ... maybe 1x per day? I'm not proposing to log-out the user after IP change, I'm proposing to keep multiple sessions (on server) / auth cookies (on client) for each IPv4 or IPv6 prefix (let's say /56).

And that JavaScript has access to cookies, that’s just a basic part of how web browsers work. Lemmy can’t do anything to prevent that.

Yes and No. Cookies could be accessed by JS on the client. BUT. When the cookie is sent by the server with additional HttpOnly header, then the cookie cannot be accessed from JS. Look at Lemmy GitHub issue, they discuss exactly this. Lemmy server absolutely has power to prevent this.

Again, Lemmy can’t do anything about that. Once there’s a vulnerability that allows an attacker to inject arbitrary JS into the site, Lemmy can’t do anything to prevent that JS from making requests.

I believe they can. But I'm not sure about this one. The server could send a response preventing the web browser to request content from other domains. Banks are using this. There was an attack years ago when attacker created a web page with i-frame in it. The i-frame was full screen to confuse the victim it is actually using the Banks site and not the attacker site. The bank web site was inside the inner i-frame, the code in the outer frame then had access to sensitive data in the inner frame. I believe there are HTTP response headers that instruct the web browser to not allow this. But I'm not sure I remember how exactly this works.

completely independent backend

Yes, it would be more costly, but more secure. It is trade-off, which one is more important to you? In case of chat/blog/forum app such as Lemmy I prefer cheap, in case of my Bank website I prefer secure.

Oh I forgot another line of defense / basic security mitigation. If a server produces an access token (such as JWT or any other old school cookie / session ID), pair it with an IP address. So in case of cookie theft, the attacker cannot use this cookie from his computer (IP address). If the IP changes (mobile / WiFi / ADSL / whatever), the legitimate user should log-in again, now storing two auth cookies. In case of another IP change, no problemo, one of the stored cookies will work. Of course limit validity of the cookie in time (lets, say, keep it valid only for a day or for a week or so).

So what happened:

• Someone posted a post.
• The post contained some instruction to display custom emoji.
• So far so good.
• There is a bug in JavaScript (TypeScript) that runs on client's machine (arbitrary code execution?).
• The attacker leveraged the bug to grab victim's JWT (cookie) when the victim visited the page with that post.
• The attacker used the grabbed JWTs to log-in as victim (some of them were admins) and do bad stuff on the server.

Am I right?

I'm old-school developer/programmer and it seems that web is peace of sheet. Basic security stuff violated:

• User provided content (post using custom emojis) caused havoc when processing (doesn't matter if on server or on client). This is lack of sanitization of user-provided-data.
• JavaScript (TypeScript) has access to cookies (and thus JWT). This should be handled by web browser, not JS. In case of log-in, in HTTPS POST request and in case of response of successful log-in, in HTTPS POST response. Then, in case of requesting web page, again, it should be handled in HTTPS GET request. This is lack of using least permissions as possible, JS should not have access to cookies.
• How the attacker got those JWTs? JavaScript sent them to him? Web browser sent them to him when requesting resources form his server? This is lack of site isolation, one web page should not have access to other domains, requesting data form them or sending data to them.
• The attacker logged-in as admin and caused havoc. Again, this should not be possible, admins should have normal level of access to the site, exactly the same as normal users do. Then, if they want to administer something, they should log-in using separate username + password into separate log-in form and display completely different web page, not allowing them to do the actions normal users can do. You know, separate UI/applications for users and for admins.

Am I right? Correct me if I'm wrong.

Again, web is peace of sheet. This would never happen in desktop/server application. Any of the bullet points above would prevent this from happening. Even if the previous bullet point failed to do its job. Am I too naïve? Maybe.

Marek.