5 ms·

If you are knowledgable enough to MITM SSL then you should definitely be knowledgable enough to know how stupid this is, and - frankly - knowledgable enough not

If you are knowledgable enough to MITM SSL then you should definitely be knowledgable enough to know how stupid this is, and - frankly - knowledgable enough not to fucking MITM SSL. I would attribute it to malice, assume it's malice, fire the developer, and contact the authorities. Of course, that's moot if the authorities are the ones who asked for the bug.

tptacek 10y ago
Let's try a little exercise here. Stipulate that it's malice, and then generate the narrative in which malice makes sense. Specifically: You are whatever entity (I assume the FSB?) that can demand Kaspersky implant backdoors into its desktop antivirus software. You decide to target that backdoor at the component of Kaspersky's software that gets, by design, unrestricted access to the plaintext of all TLS sessions on the machine, in addition to practically unrestricted access to every file on machine itself, and to the machine's memory in cpl0 and cpl3. From that vantage point, you decide to... ... collide certificates? Remember, your evil backdoor only impacts machines running your software already. From this thread, I'm wondering if that's maybe unclear to people.
- Sir_Cmpwn 10y ago
  Did you read the link? It describes an attack where you only need to have access to the same network as the target. Perhaps through that smart lightbulb they just installed?
  - tptacek 10y ago
    Yes, I did read the link. Do you understand the thread? The proposal is that this bug in Kaspersky's kernel code is a backdoor in Kaspersky's kernel code --- that is: an attacker that already owns your OS kernel is backdooring it to come up with an extremely convoluted and noisy way to get access to your TLS sessions --- by backdooring the part of their kernel code that already has access to every TLS session on the machine.
    - Sir_Cmpwn 10y ago
      The described attack doesn't sound convoluted at all, it seems very practical.
      - tptacek 10y ago
        Once again: the attacker here already controls TLS on the machines that are affected. They don't need to collide certificates. By design, they not only have the plaintext of every TLS session on the machine, but they are also the client side of every TLS session originating from the machine (they terminate TLS locally and proxy it over a new connection they control). I feel like the people claiming this is a smoking gun backdoor don't really understand what it means that Kaspersky's software is designed to proxy TLS. Yes: it is batshit that they proxy TLS. It's so batshit that this particular bug makes absolutely no sense as a backdoor. That idea is Xzibit-level crazy.
        Sir_Cmpwn 10y ago
        I see what you mean now. If you wanted to make a backdoor and have plausable deniability, you'd make it a bug.
        tptacek 10y ago
        Yes, but you would not make it this bug, which (a) doesn't get you any access you don't already have, and (b) leaves a trail of sporadically broken TLS connections so obvious that they show up in CT logs.
        Sir_Cmpwn 10y ago
        No, you don't understand. They already had that access, but in order to exploit it they (hypothetically) need a sneaky way to do so. Hence the bug.
        tptacek 10y ago
- jamesrom 10y ago
  Let's continue your exercise. Your backdoor gets detected by any security researcher. You're busted, your business is near destroyed, you cause diplomatic stress between nations and, you face criminal charges. The stakes are way too high. So instead you consider ways to introduce vulnerabilities that leave plausible deniability. Indeed, from that vantage point, you decide to... ... collide certificates.
  - tptacek 10y ago
    So you propose that they created a backdoor that regularly and sporadically breaks TLS for normal users because they are evil geniuses who needed a plausibly stupid backdoor in case they got caught. Not only are there better plausibly deniable backdoors they could use from this vantage point, but there are NOBUS backdoors they could use from this vantage point. You propose an attacker so clever that they've carefully calibrated the sophistication of their backdoors, but not clever enough to know how to backdoor a TLS MITM (a TLS MITM installed by design) without leaving the absurd tracks this one does. No. It's not a conspiracy. As usual: it's just a bug.
- sigmar 10y ago
  >Let's try a little exercise here. Stipulate that it's malice, and then generate the narrative in which malice makes sense. Sure. Kaspersky creates security software. The FSB benefits from vulnerabilities in antivirus software. Kaspersky knows this and puts company resources into particular areas. ie how to spot the next stuxnet, rather than fix bugs like this. The FSB does not need to write the source code (for Kaspersky Anti-virus) to benefit from vulnerabilities. In fact NSA, GCHQ, and FSB all benefit from subversion of https.
  - tptacek 10y ago
    You can't stop at that point in my comment. You have to read the whole thing first. I'm not asking "does it ever make sense to backdoor Kaspersky AV". Clearly it does.
    - sigmar 10y ago
      I did. You created a ridiculous narrative, that seems to amount to a strawman. No one ever said that FSB wrote the antivirus program.
      - tptacek 10y ago
        My narrative has in fact nothing whatsoever to do with the FSB. That's why I said "whatever entity".
        sigmar 10y ago
        "your evil backdoor only impacts machines running your software already. " seems to assume that "whatever entity" can freely put in whatever code they want. I agree that cert collisions is a strange way to backdoor, but to dismiss any questions as to possible malice as "conspiracy theories" seems to ignore many recent events (such as Juniper Networks)
        tptacek 10y ago
        Once again, you're responding to an argument I did not make. I'm not saying this bug doesn't make sense because nobody would want to backdoor Kaspersky AV. Clearly they would. I'm saying it doesn't make sense because it doesn't make sense as a backdoor. It provides the attacker with far less access than they already have, and does so in a way that leaves tracks all over the Internet even when the "backdoor" isn't "in use".

tptacek 10y ago

Let's try a little exercise here. Stipulate that it's malice, and then generate the narrative in which malice makes sense. Specifically: You are whatever entity (I assume the FSB?) that can demand Kaspersky implant backdoors into its desktop antivirus software. You decide to target that backdoor at the component of Kaspersky's software that gets, by design, unrestricted access to the plaintext of all TLS sessions on the machine, in addition to practically unrestricted access to every file on machine itself, and to the machine's memory in cpl0 and cpl3. From that vantage point, you decide to... ... collide certificates? Remember, your evil backdoor only impacts machines running your software already. From this thread, I'm wondering if that's maybe unclear to people.

Sir_Cmpwn 10y ago
Did you read the link? It describes an attack where you only need to have access to the same network as the target. Perhaps through that smart lightbulb they just installed?
- tptacek 10y ago
  Yes, I did read the link. Do you understand the thread? The proposal is that this bug in Kaspersky's kernel code is a backdoor in Kaspersky's kernel code --- that is: an attacker that already owns your OS kernel is backdooring it to come up with an extremely convoluted and noisy way to get access to your TLS sessions --- by backdooring the part of their kernel code that already has access to every TLS session on the machine.
  - Sir_Cmpwn 10y ago
    The described attack doesn't sound convoluted at all, it seems very practical.
    - tptacek 10y ago
      Once again: the attacker here already controls TLS on the machines that are affected. They don't need to collide certificates. By design, they not only have the plaintext of every TLS session on the machine, but they are also the client side of every TLS session originating from the machine (they terminate TLS locally and proxy it over a new connection they control). I feel like the people claiming this is a smoking gun backdoor don't really understand what it means that Kaspersky's software is designed to proxy TLS. Yes: it is batshit that they proxy TLS. It's so batshit that this particular bug makes absolutely no sense as a backdoor. That idea is Xzibit-level crazy.
      - Sir_Cmpwn 10y ago
        I see what you mean now. If you wanted to make a backdoor and have plausable deniability, you'd make it a bug.
        tptacek 10y ago
        Yes, but you would not make it this bug, which (a) doesn't get you any access you don't already have, and (b) leaves a trail of sporadically broken TLS connections so obvious that they show up in CT logs.
        Sir_Cmpwn 10y ago
        No, you don't understand. They already had that access, but in order to exploit it they (hypothetically) need a sneaky way to do so. Hence the bug.
        tptacek 10y ago
jamesrom 10y ago
Let's continue your exercise. Your backdoor gets detected by any security researcher. You're busted, your business is near destroyed, you cause diplomatic stress between nations and, you face criminal charges. The stakes are way too high. So instead you consider ways to introduce vulnerabilities that leave plausible deniability. Indeed, from that vantage point, you decide to... ... collide certificates.
- tptacek 10y ago
  So you propose that they created a backdoor that regularly and sporadically breaks TLS for normal users because they are evil geniuses who needed a plausibly stupid backdoor in case they got caught. Not only are there better plausibly deniable backdoors they could use from this vantage point, but there are NOBUS backdoors they could use from this vantage point. You propose an attacker so clever that they've carefully calibrated the sophistication of their backdoors, but not clever enough to know how to backdoor a TLS MITM (a TLS MITM installed by design) without leaving the absurd tracks this one does. No. It's not a conspiracy. As usual: it's just a bug.
sigmar 10y ago
>Let's try a little exercise here. Stipulate that it's malice, and then generate the narrative in which malice makes sense. Sure. Kaspersky creates security software. The FSB benefits from vulnerabilities in antivirus software. Kaspersky knows this and puts company resources into particular areas. ie how to spot the next stuxnet, rather than fix bugs like this. The FSB does not need to write the source code (for Kaspersky Anti-virus) to benefit from vulnerabilities. In fact NSA, GCHQ, and FSB all benefit from subversion of https.
- tptacek 10y ago
  You can't stop at that point in my comment. You have to read the whole thing first. I'm not asking "does it ever make sense to backdoor Kaspersky AV". Clearly it does.
  - sigmar 10y ago
    I did. You created a ridiculous narrative, that seems to amount to a strawman. No one ever said that FSB wrote the antivirus program.
    - tptacek 10y ago
      My narrative has in fact nothing whatsoever to do with the FSB. That's why I said "whatever entity".
      - sigmar 10y ago
        "your evil backdoor only impacts machines running your software already. " seems to assume that "whatever entity" can freely put in whatever code they want. I agree that cert collisions is a strange way to backdoor, but to dismiss any questions as to possible malice as "conspiracy theories" seems to ignore many recent events (such as Juniper Networks)
        tptacek 10y ago
        Once again, you're responding to an argument I did not make. I'm not saying this bug doesn't make sense because nobody would want to backdoor Kaspersky AV. Clearly they would. I'm saying it doesn't make sense because it doesn't make sense as a backdoor. It provides the attacker with far less access than they already have, and does so in a way that leaves tracks all over the Internet even when the "backdoor" isn't "in use".