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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]

#51

Post by cesarb »

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

I haven't seen it mentioned anywhere yet, but I have to wonder... Does this vulnerability allow MITM of Windows Update itself?

I would expect all connections to the Windows Update servers to be protected with TLS, and as a second layer the updates themselves to be signed, but if this vulnerability allows bypassing both signatures, this could be really bad.

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

#52

Post by ynik »

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

The attack allows faking https certs as well as code signing certs; so it seems plausible that a MitM attacker could trick Windows Update (or other auto-updaters) into executing malicious code.

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

#53

Post by heartbreak »

ynik wrote: post #52
richardwhiuk wrote: post #40

Earlier quoted context omitted.

"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

The attack allows faking https certs as well as code signing certs; so it seems plausible that a MitM attacker could trick Windows Update (or other auto-updaters) into executing malicious code.

That this exploit can be used to spoof the Windows Update system is a big yikes. You can’t necessarily trust today’s update itself.

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

#54

Post by idlewords »

toyg wrote: post #34
ct520 wrote: post #28

Earlier quoted context omitted.

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.

They have probably done that for a while (this is the first public attribution , not the first disclosure); but they are now blowing their trumpet because they need some good PR. Why? Snowden.

Much more likely the bad reaction to Eternal Blue.

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

#55

Post by mzs »

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

I read it simply as malicious update passes as from a trusted source due to this vuln and the malicious update runs it's code as part of the update process, not as a buffer overflow or something of that sort.

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

#56

Post by mike_d »

cesarb wrote: post #51
richardwhiuk wrote: post #40

Earlier quoted context omitted.

"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

I haven't seen it mentioned anywhere yet, but I have to wonder... Does this vulnerability allow MITM of Windows Update itself? I would expect all connections to the Windows Update servers to be protected with TLS, and as a second layer the updates themselves to be signed, but if this vulnerability allows bypassing both signatures, this could be really bad.

It does allow you to modify TLS streams (the WU downloads), and code signing (checking that a binary can run), but it is unclear if any of the trusted WU validation keys (confirming the update is from a signed manifest) are ECC.

So: maybe.

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

#57

Post by tptacek »

cesarb wrote: post #51
richardwhiuk wrote: post #40

Earlier quoted context omitted.

"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

I haven't seen it mentioned anywhere yet, but I have to wonder... Does this vulnerability allow MITM of Windows Update itself? I would expect all connections to the Windows Update servers to be protected with TLS, and as a second layer the updates themselves to be signed, but if this vulnerability allows bypassing both signatures, this could be really bad.

This attack targets the nuts and bolts of how the Windows platform actually implements TLS; a vulnerability in CryptoAPI that allowed you spoof any ECC certificate would presumably break all of TLS. What might mitigate this in Windows Software Update would be some kind of key pinning that prevented arbitrary certificates from being used.

Later

Dmitri Alperovitch at Crowdstrike says this doesn't impact Windows Update.

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

#58

Post by bodeadly »

SlowRobotAhead wrote: post #42
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…

So... Wait, they weren't calculating the signature based on ALL the contents of the cert? There was an "unprotected" section in the cert that allowed for curve details? This seems... too obviously bad.

Not exactly but I'm not sure it matters. It sounds like if the curve parameters are crafted just-so, they can dodge validation and use anyone's public key and yet still negotiate successfully and decrypt everything. The "gramdma" explaination is basically the green lock next to the URL in your browser doesn't mean spit at this particular moment in time.

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

#59

Post by mzs »

SlowRobotAhead wrote: post #42
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…

So... Wait, they weren't calculating the signature based on ALL the contents of the cert? There was an "unprotected" section in the cert that allowed for curve details? This seems... too obviously bad.

Basically there are standard curves and software assumed parameters matched, bad design.

edit: more detail

https://news.ycombinator.com/item?id=22048619

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