For a reflected XSS? Tell me who is paying that much for such a relatively common bug...

To elaborate, to exploit this you have to convince your target to open a specially crafted link which would look very suspect. The most realistic way to exploit would be to send a shortened link and hope they click on it, that they are logged into discord.com when they do (most people use the app), that there are no other security measures (httponly cookies) etc

No real way to use this to compromise a large amount of users without more complex means

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PenguinCoder 17 hours ago | parent | next [-]

It isn't about the commonality of the bug, but the level of access it gets you on the type or massive scale of the target. This bug you your blog? Who cares. This bug on Discord or AWS? Much more attractive and lucrative.

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mpeg 16 hours ago | parent | next [-]

Yes, but this is not a particularly high access level bug.

Depending on the target, it's possible that the most damage you could do with this bug is a phishing attack where the user is presented a fake sign-in form (on a sketchy url)

I think $4k is a fair amount, I've done hackerone bounties too and we got less than that years ago for a twitter reflected xss

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rvnx 15 hours ago | parent [-]

Why would that be the maximum damage ? This XSS is particularly dangerous because you are running your script on the same domain where the user is logged-in so you can pretty much do anything you want under his session.

In addition this is widespread. It's golden for any attacker.

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0x3f 15 hours ago | parent [-]

Because modern cookie directives and browser configs neuter a lot of the worst XSS outcomes/easiest exploit paths. I would expect all the big sites to be setting them, though I guess you never know.

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rvnx 15 hours ago | parent | next [-]

I would not be that confident as you can see: on their first example, they show Discord and the XSS code is directly executed on Discord.com under the logged-in account (some people actually use web version of Discord to chat, or sign-in on the website for whatever reason).

If you have a high-value target, it is a great opportunity to use such exploits, even for single shots (it would likely not be detected anyway since it's a drop in the ocean of requests).

Spreading it on the whole internet is not a good strategy, but for 4000 USD, being able to target few users is a great value.

Besides XSS, phishing has its own opportunity.

Example: Coinbase is affected too though on the docs subdomain and there are 2-step, so you cannot do transactions directly but if you just replace the content with a "Sign-in to Coinbase / Follow this documentation procedure / Download update", this can get very very profitable.

Someone would pay 4000 USD to receive 500'000 USD back in stolen bitcoins).

Still, purely with executing things under the user sessions there are interesting things to do.

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promiseofbeans 4 hours ago | parent | next [-]

> some people actually use web version of Discord to chat, or sign-in on the website for whatever reason

Beside this security blunder on Discord’s part, I can see only upsides to using a browser version rather than an Electron desktop app. Especially given how prone Discord are to data mining their users, it seems foolish to let them out of the web sandbox and into your system

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tptacek 14 hours ago | parent | prev [-]

Again, here you have not so much sold a vulnerability as you have planned a heist. I agree, preemptively: you can get a lot of money from a well-executed heist!

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rvnx 14 hours ago | parent [-]

Do you want to execute actions as logged-in user on high-value website XXX ?

If yes -> very useful

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tptacek 14 hours ago | parent [-]

Nobody is disputing that a wide variety of vulnerabilities are "useful", only that there's no market for most of them. I'd still urgently fix an XSS.

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rvnx 14 hours ago | parent [-]

There is a market outside Zerodium, it's Telegram. Finding a buyer takes time and trust, but it has definitively higher value than 4k USD because of its real-world impact, no matter if it is technically lower on the CVSS scores.

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tptacek 14 hours ago | parent [-]

Really? Tell me a story about someone selling an XSS vulnerability on Telegram.

("The CVSS chart"?)

Moments later

Why do people keep bringing up "Zerodium" as if it's a thing?

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rvnx 13 hours ago | parent [-]

I understand your perspective about the technical value of an exploit, but I disagree with the concept that technical value = market value.

There are unorganized buyers who may be interested if they see potential to weaponize it.

In reality, if you want to maximize revenue, yes, you need to organize your own heist (if that's what you meant)

	▲	tptacek 10 hours ago \| parent [-]
		Do you know this or do you just think it should be true?

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GoblinSlayer 3 hours ago | parent | prev [-]

AIU this feature is SSS, not XSS, so XSS protections don't apply.

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0x3f 16 hours ago | parent | prev [-]

How would you make money from this? Most likely via phishing. Not exactly a zero-click RCE.

	▲	tptacek 16 hours ago \| parent [-]
		What happens in all these discussions is that we stealthily transition from "selling a vulnerability" to "planning a heist", and you can tell yourself any kind of story about planning a heist.

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varenc 12 hours ago | parent | prev [-]

Also the XSS exploit would have been dead in the water for any sites using CSP headers. Coinbase certainly uses CSP. With this in place an XSS vuln can't inject arbitrary JS.