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Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

media.defense.gov

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Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#71

Post by tptacek »

mzs wrote: post #70
tptacek wrote: post #48

From a conversation with Thomas Pornin, a plausible explanation given the details provided in the DoD advisory: Given an ECDSA signature and control over the curve domain parameters, it's straightforward to create a second private key that matches the original public key, without knowledge of the original signing private key. Here's how: To start with, you need to understand a little bit about how curve cryptography…

The important part might be just how hard it is to come-up with G'.

As you can see, it's not at all hard.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#72

Post by Uptrenda »

richardwhiuk wrote: post #40
Uptrenda wrote: post #22

None of these links describe how the exploit works. I found this: https://media.defense.gov/2020/Jan/14/2002234275/-1/-1/0/CSA... So based on my limited understanding: 1. The certificates have a place for defining curve parameters. 2. The attacker specifies their own parameters so that they match the start of a standard curve but choose the rest of the parameters themselves. With the right ECC math they are able to g…

"enable remote code execution." suggests it's worse than that - like the curve parameters might allow a buffer overflow, or something of that nature. Maybe they just mean because it can sign Authenticode signatures

It's scarier the more you think about it because digital sigs are the first place you look for most "secure protocols." I think reading between the lines there are multiple attack scenarios:

- Fake windows updates

- The notorious SMB protocol -- "The Server Message Block (SMB) protocol provides the basis for file and print sharing and many other networking operations, such as remote Windows administration. To prevent man-in-the-middle attacks that modify SMB packets in transit, the SMB protocol supports the digital signing of SMB packets." Could prob impersonate a Windows server or computer in a home group, IDK.

- Likely fractal attacks on active directory that would allow injecting admin accounts on any work station in a network and enabling remote desktop.

- Fake SSL certs -- also: hey user, here's a [trojan] to fix the latest Windows vuln [fake Microsoft.com]. It's a race to update with the offical update, really. If attackers were to DDoS the update service, it would be very very bad.

- Fake signed trusted programs that security software may "ignore" and that windows itself would allow to run with fewer warnings. Trusted MS programs could be a very good way to write persistent root kits.

I'm sure windows experts can think of more stuff. But for me it's a good lesson for how much we depend on the certificate system for security.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#73

Post by trulyrandom »

The advisory from Microsoft is quite bizarre. It focuses on code signature validation, rather than X.509 as a whole. It also doesn't say anything about how the vulnerability itself works. Vague advisories like this are dangerous, because it gives adversaries an advantage over IT departments that don't know which system they should patch first. It would be much better if everyone understood exactly what the impact is from the get go. The NSA advisory is a bit better, but still doesn't tell us how exactly the ECC certificate validation bug works. We're left with only a few hints.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#74

Post by mastazi »

tptacek wrote: post #48

From a conversation with Thomas Pornin, a plausible explanation given the details provided in the DoD advisory: Given an ECDSA signature and control over the curve domain parameters, it's straightforward to create a second private key that matches the original public key, without knowledge of the original signing private key. Here's how: To start with, you need to understand a little bit about how curve cryptography…

Mobile users: there is a “p” at the end of the equation, it is hidden due to the type of code formatting that HN uses.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#75

Post by blaser-waffle »

mzs wrote: post #64
kornholi wrote: post #3

From Krebs tweets: The NSA's Neuberger said this wasn't the first vulnerability the agency has reported to Microsoft, but it was the first one for which they accepted credit/attribution when MS asked. Sources say this disclosure from NSA is planned to be the first of many as part of a new initiative at NSA dubbed "Turn a New Leaf," aimed at making more of the agency's vulnerability research available to major softwar…

The tweet* from the call with reporters - a cynical person might think instead that NSA thought that with the similarity to the LE and FF flaws it was not much longer before a hostile actor would find this crypt.dll flaw so it was time to notify MS. * https://twitter.com/briankrebs/status/1217125030452256768

Didn't the FBI or NSA push for flawed Elliptical Curve Crypto in the past?

Could be the knew about it for a while and had milked it hard until they caught someone else using it. Or like the parent said, previously discovered flaws meant that someone might catch this one, too.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#76

Post by gruez »

vermilingua wrote: post #60

Could someone clarify: does this allow the creation of fake certificates that are accepted as authentic by any crypto library? Or rather, does it treat such faked certificates as authentic itself?

> Could someone clarify: does this allow the creation of fake certificates that are accepted as authentic by any crypto library?

No, only the Windows native one. For instance, Firefox (which uses NSS) would be safe.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#77

Post by diffeomorphism »

thfuran wrote: post #46
eyegor wrote: post #9

Earlier quoted context omitted.

They are paid to collect intelligence for the benefit of the american people, not american companies. Luckily citizens united hasn't stretched that far.

You don't see how a lack of critical vulnerabilities is software infrastructure is of benefit to citizens?

No, I don't see how this is part of foreign intelligence/surveillance/espionage work. It is good that these vulnerabilities are fixed, of course. But shouldn't that be at least a separate partially independent branch of the NSA? Otherwise you get a large conflict of interest.

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#78

Post by jka »

ct520 wrote: post #28
kornholi wrote: post #3

From Krebs tweets: The NSA's Neuberger said this wasn't the first vulnerability the agency has reported to Microsoft, but it was the first one for which they accepted credit/attribution when MS asked. Sources say this disclosure from NSA is planned to be the first of many as part of a new initiative at NSA dubbed "Turn a New Leaf," aimed at making more of the agency's vulnerability research available to major softwar…

more like someone with some commonsense decided to capitalize on disclosing issues when other countries get zero days. Oh well, guess we can't use this anymore Bob, china has been exploiting it over the past week. Call Microsoft lets at least get some free PR in exchange of having to give this up.

An alternative angle that could make sense is that it shows that they're not purely intent on hoarding exploits (particularly dangerous ones) and are willing to report them to software vendors in order to reduce everyone's risk profile.

That'd be more of a communal-good, de-escalation approach. There's certainly something to be said for the fact that it displays the talent and expertise available too though (i.e. helping for recruitment).

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#79

Post by [deleted] »

tptacek wrote: post #25
Uptrenda wrote: post #22

None of these links describe how the exploit works. I found this: https://media.defense.gov/2020/Jan/14/2002234275/-1/-1/0/CSA... So based on my limited understanding: 1. The certificates have a place for defining curve parameters. 2. The attacker specifies their own parameters so that they match the start of a standard curve but choose the rest of the parameters themselves. With the right ECC math they are able to g…

Good find. This page should almost certainly be the headline article on HN, at least until someone does a full write-up of the vulnerability --- but the vulnerability here looks very simple (and gross ): if you can define your own curve parameters and get CryptoAPI to honor them, you can sign anything.

[deleted]

Re: Patch Critical Cryptographic Vulnerability in Microsoft Windows [pdf]

#80

Post by Godel_unicode »

munchbunny wrote: post #61
Uptrenda wrote: post #22

None of these links describe how the exploit works. I found this: https://media.defense.gov/2020/Jan/14/2002234275/-1/-1/0/CSA... So based on my limited understanding: 1. The certificates have a place for defining curve parameters. 2. The attacker specifies their own parameters so that they match the start of a standard curve but choose the rest of the parameters themselves. With the right ECC math they are able to g…

I wonder what happens at the Microsoft Security Response Center when a big vuln hits like this? Does it tie up all their resources just working on the one vuln? Generally no, if only because of Microsoft’s sheer size. For something like this issue, while its potential impact is big, I would guess that it only tied up the team(s) that work on CryptoAPI.

And Windows defender.
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