9 ms·

Would you mind elaborating on the good reasons for MITM your company web traffic? I'm not being facetious, genuinely curious.

by sekasi 12y ago

tptacek 12y ago
For instance, if you are a company that handles confidential medical information (any health care organization, many insurers, every employee benefits management organization, &c), you may be required to have controls in place to ensure that nobody uses your Internet connection to exfiltrate people's PII through Google Mail. Similarly, many investment banks and financial information firms have strict requirements to monitor all communications owing to SEC rules and insider trading regulation.
- mjs 12y ago
  Is there any way to detect that you're being MITM'd?
  - bradleyjg 12y ago
    You check the certificate chain and compare it to a clean version. Obviously that's going to be a solution limited to very savvy users.
  - tptacek 12y ago
    That's part of the point of certificate pinning.
  - aslewofmice 12y ago
    Would love to know this as well. I only have a high level understanding of the purpose of CA Certs, but beyond that I'm lost. Ignorant questions ahoy: 1. Using Chrome, would you have to manually accept the MITM certificate? 2. Could such a certificate be valid across multiple domains? 3. Would it pose any threat to the computer if it was moved from the MITM network to an outside network? 4. What kind of potential problems could occur if I issued a self-signed certificate for my network?
    - minot 12y ago
      Check the certificate store for the browser you are using. Mozilla Firefox has its own. Internet Explorer and Chrome on Windows rely on the Windows certificate store. http://windows.microsoft.com/en-us/windows-vista/view-or-manage-your-certificates http://windows.microsoft.com/en-us/windows-vista/view-or-man... Details on what certificates come with your installation of Mozilla Firefox: https://www.mozilla.org/en-US/about/governance/policies/security-group/certs/ https://www.mozilla.org/en-US/about/governance/policies/secu... Your organization may add their own certificates as described below: https://www.utexas.edu/its/help/user-certs/817 https://www.utexas.edu/its/help/user-certs/817
    - Lynbarry 12y ago
      As far as I understand it (please someone correct me if I'm wrong): 1. In this case you would not have to manually accept anything, as the root certificate (the CNNIC cert) is already in your browser/os and the certificate chain for certs created by MCS would be OK (because their cert is signed by CNNIC). 2. As CNNIC issued them an intermediate CA cert, MCS was able to create certificates for any domain they wanted and these certificates would be considered valid by everyone that has CNNIC in the root store. So the MCS cert is not valid accross multiple domains, but it allows MCS to create certificates for every domain which kind of has the same consequences. 3. I think it would pose a threat when leaving the MITM network, but not as a consequence of having been in the MITM network. Only the root certificates are stored locally. Websites have to send a complete certificate chain that anchors their certs in one of the root certs. This means that the cert generated by MCS is not stored and therefore not used when leaving the network anymore. The danger is that this intermediate cert allows MCS to generate certs for any domain and use them outside their network, too. 4. A self signed certificate would have to be installed on the machines in the network. Otherwise users would get a certificate warning and would have to add the cert to their rootstores themselves. Other than that I think that this would grant you the same MITM-powers as this intermediate cert did for MCS, with the only restriction that you couldn't create certs for domains not in your control that would be accepted by users outside your network/that don'd have your self signed cert installed.
  - itistoday2 12y ago
    > Is there any way to detect that you're being MITM'd? Yes, a project we're working on called DNSChain prevents MITM attacks for domains that have their info stored in a blockchain. We're maintaining a list of alternatives and how they compare to DNSChain here: https://github.com/okTurtles/dnschain/blob/master/docs/Comparison.md https://github.com/okTurtles/dnschain/blob/master/docs/Compa...
  - zaroth 12y ago
    It's the golden unsolved, perhaps unsolvable problem in crypto. Trusting trust and such. There's always a key, somewhere, that has to be shared. One way to hack the system is if you have actual knowledge of the person you are talking to, and you assume some limited amount of tampering which can be done in real-time. For example, if I know the sound of your voice, and we want to agree on a key with no MITM, we can setup an audio channel and speak some code words to each other. Baring an adversary which can in real-time intercept and synthesize my voice convincingly speaking a different code, this is pretty secure. [1] [ZRTP] allows the detection of man-in-the-middle (MiTM) attacks by displaying a short authentication string (SAS) for the users to read and verbally compare over the phone. Another imperfect defense is spreading over time the data that an attacker would have to intercept and modify in order to MITM. That's what Chrome is doing with their pin lists. Now an adversary would have to alter the pinning when Chrome is downloaded. Of course in this very thread we're talking about technology which can do exactly that. E.g. technology which has any hope of preventing data exfiltration, would have an easy time altering Chrome's pin-list. Of course the Chrome binaries are signed, so there's another layer to defeat, etc. etc. So the end result is there are a lot of good technologies to prevent MITM. If you can keep the attacker out once, you can generally be confident your future conversations will be secure as well, since good protocols don't start from scratch each time, but rather "ratchet" new keys from the old as you go. [2] One of the big trade-offs is false positives and privacy. For example, it might be nice if my browser remembered the public key of a site I visit, like HN, and let me know if it changed. Two issues are a naive implementation would also serve as a great tracker for every site I've visited, and how do I know if when I get a warning, it's a real attack and not just an expiring certificate rotating out? Now we would need a way for sites to indicate, by signing with their old key, that indeed they are switching to a new key, and complexity explodes from there. [1] - http://blog.cryptographyengineering.com/2012/11/lets-talk-about-zrtp.html http://blog.cryptographyengineering.com/2012/11/lets-talk-ab... [2] - https://whispersystems.org/blog/advanced-ratcheting/ https://whispersystems.org/blog/advanced-ratcheting/
    - mjs 12y ago
      > It's the golden unsolved, perhaps unsolvable problem in crypto. Sorry, perhaps my question wasn't clear. I wasn't asking about MITM in the general case, I was asking about this particular case. The certificate chain for Hacker News seems to go AddTrust -> COMODO -> Another COMODO -> *.ycombinator.com. So in this case, if you're MITM'd by MCS Holdings, is MCS Holdings going to be part of the chain (after a CNNIC)?
  - JeffCyr 12y ago
    For web site with authentication (e.g. bank account), protocols like SRP (Secure Remote Password) would prevent the man-in-the-middle if he doesn't know your password. SRP is a mutual authentication protocol with zero knowledge and forward secrecy, it would be nice if major browsers supported it, it's not usable without browser support.
- jsprogrammer 12y ago
  > if you are a company that handles confidential medical information (any health care organization, many insurers, every employee benefits management organization, &c), you may be required to have controls in place to ensure that nobody uses your Internet connection to exfiltrate people's PII through Google Mail. Yes, but what are those controls? You check every packet to see if it contains any information from one of your databases? What if the person sending the data just applies a simple obfuscation technique to the data, or just tunnels through some other encryption scheme? Edit: downmods? really?
  - acdha 12y ago
    Search for things like “data loss appliance”. As an example, when BlueCoat isn't helping repressive regimes spy on their citizens, they're helping businesses watch every outgoing packet: https://www.bluecoat.com/products/dlp https://www.bluecoat.com/products/dlp “Blue Coat DLP allows you to easily create policies that analyze the data source, content, destination and more. … accurate data “fingerprinting” capabilities, in addition to powerful keyword, pattern, and regular expression support, so you can create precision policies to effectively secure your data while minimizing false positives.” Sure, the every HN reader might have questions about this but I'd bet a LOT of C-level executives are receptive to this.
    - kjs3 12y ago
      What questions do you have? Limiting the scope of discovery to fingerprinted data is a pretty good way to limit "incidental" data filtering/discovery.
      - acdha 12y ago
        Oh, sorry, I meant questions like the ones raised about how someone might try to smuggle data past such filters or some of the security aspects of having a single point with access to everything. I certainly agree that if you have a requirement to watch outbound data like this, having a system to selectively capture it is much better than simply attempting to record everything.
  - 12y ago
- cesarb 12y ago
  What if the site you're accessing is required to have controls in place to ensure that nobody can intercept the communication between the user and the site? I'd expect that to be the case when the site handles things like confidential medical information.
  - snowwrestler 12y ago
    When you are using your employer's computing equipment on your employer's premises, you have limited right to privacy.
  - kjs3 12y ago
    In a typical deployment of MitM tech (e.g. Bluecoat, Websense, etc.), things like personal banking, health care sites, etc., are exempted from the interception policy to avoid personal privacy issues and HR headaches. This can be overridden in the local policy of course, but I've rarely seen that in practice (anecdote isn't fact, blah, blah). Be aware that the site you're going to may be MitM'ing sessions to meet other compliance regulations (e.g. SOX in the financial sector).
    - cesarb 12y ago
      > In a typical deployment of MitM tech (e.g. Bluecoat, Websense, etc.), things like personal banking, health care sites, etc., are exempted from the interception policy to avoid personal privacy issues and HR headaches. How does it know? Does it have a list of all "personal banking, healthcare sites, etc" from the whole world? How is that list kept up-to-date? What happens if the site the employee is accessing is missing from the list? What happens if the employee knows these sites aren't monitored and finds a way to use them to bypass the monitoring? > Be aware that the site you're going to may be MitM'ing sessions to meet other compliance regulations (e.g. SOX in the financial sector). If it's the site itself, is it really a MITM? And even if they technically use a MITM, does it really matter, since the site would have access to the plaintext anyways?
    - deleted 12y ago
      [deleted]
Stefan-H 12y ago
All of the reasons that benefit the company. Data Loss Prevention, web filtering, malware detection, take your pick.
- bradleyjg 12y ago
  While there may well be good reasons to MitM HTTPS on a corporate network, the case isn't quite so clear for secretly doing so. IIRC chrome disables altogether certificate pin violation notifications if the offending certificate is locally installed. While it probably is the right move to forgo the giant security warning in that case, I don't see why they can't use an "orange light" type indicator and in the popup explain corporate monitoring (with a further note that if you aren't on an institutional computer you probably have a virus). While corporate IT departments could recompile chromium sans message, or just ban chrome altogether, why make it easy for them?
  - Stefan-H 12y ago
    If you are using corporate hardware it should not really be secret that your traffic is being man in the middled, this should be assumed. I think it makes sense for a corporation to be able to whitelist their certificate to make intermediate network devices appear as trusted, because they are. I do agree that having a little asterisk or something for the lock ice to indicate that you are using a certificate that falls outside of the default trust store could be beneficial.
  - djrogers 12y ago
    The stuff I work with has the option to pop up a warning/comfort page to explain the practice/policies etc every N hours - seems to be a good thing to use.
Buge 12y ago
One reason would be an Intrusion Detection System: make sure no malware gets downloaded, or to analyze traffic for stuff that looks like malware phoning home. http://en.wikipedia.org/wiki/Intrusion_detection_system http://en.wikipedia.org/wiki/Intrusion_detection_system
MichaelSalib 12y ago
A good friend of mine works for a major electronics manufacturer (trust me, you'd recognize the name) where some employees exfiltrated 200,000 internal design documents/artifacts to a competitor that they were planning on joining. As a result, no one can use gmail/gchat from work machines or VPNs anymore. I think a MITM proxy that detected giant file exfils but allowed people to send gchat messages to their family would be a huge plus in that environment.

Would you mind elaborating on the good reasons for MITM your company web traffic? I'm not being facetious, genuinely curious.

by sekasi 12y ago

Would you mind elaborating on the good reasons for MITM your company web traffic? I'm not being facetious, genuinely curious.

tptacek 12y ago

For instance, if you are a company that handles confidential medical information (any health care organization, many insurers, every employee benefits management organization, &c), you may be required to have controls in place to ensure that nobody uses your Internet connection to exfiltrate people's PII through Google Mail. Similarly, many investment banks and financial information firms have strict requirements to monitor all communications owing to SEC rules and insider trading regulation.

mjs 12y ago
Is there any way to detect that you're being MITM'd?
- bradleyjg 12y ago
  You check the certificate chain and compare it to a clean version. Obviously that's going to be a solution limited to very savvy users.
- tptacek 12y ago
  That's part of the point of certificate pinning.
- aslewofmice 12y ago
  Would love to know this as well. I only have a high level understanding of the purpose of CA Certs, but beyond that I'm lost. Ignorant questions ahoy: 1. Using Chrome, would you have to manually accept the MITM certificate? 2. Could such a certificate be valid across multiple domains? 3. Would it pose any threat to the computer if it was moved from the MITM network to an outside network? 4. What kind of potential problems could occur if I issued a self-signed certificate for my network?
  - minot 12y ago
    Check the certificate store for the browser you are using. Mozilla Firefox has its own. Internet Explorer and Chrome on Windows rely on the Windows certificate store. http://windows.microsoft.com/en-us/windows-vista/view-or-manage-your-certificates http://windows.microsoft.com/en-us/windows-vista/view-or-man... Details on what certificates come with your installation of Mozilla Firefox: https://www.mozilla.org/en-US/about/governance/policies/security-group/certs/ https://www.mozilla.org/en-US/about/governance/policies/secu... Your organization may add their own certificates as described below: https://www.utexas.edu/its/help/user-certs/817 https://www.utexas.edu/its/help/user-certs/817
  - Lynbarry 12y ago
    As far as I understand it (please someone correct me if I'm wrong): 1. In this case you would not have to manually accept anything, as the root certificate (the CNNIC cert) is already in your browser/os and the certificate chain for certs created by MCS would be OK (because their cert is signed by CNNIC). 2. As CNNIC issued them an intermediate CA cert, MCS was able to create certificates for any domain they wanted and these certificates would be considered valid by everyone that has CNNIC in the root store. So the MCS cert is not valid accross multiple domains, but it allows MCS to create certificates for every domain which kind of has the same consequences. 3. I think it would pose a threat when leaving the MITM network, but not as a consequence of having been in the MITM network. Only the root certificates are stored locally. Websites have to send a complete certificate chain that anchors their certs in one of the root certs. This means that the cert generated by MCS is not stored and therefore not used when leaving the network anymore. The danger is that this intermediate cert allows MCS to generate certs for any domain and use them outside their network, too. 4. A self signed certificate would have to be installed on the machines in the network. Otherwise users would get a certificate warning and would have to add the cert to their rootstores themselves. Other than that I think that this would grant you the same MITM-powers as this intermediate cert did for MCS, with the only restriction that you couldn't create certs for domains not in your control that would be accepted by users outside your network/that don'd have your self signed cert installed.
- itistoday2 12y ago
  > Is there any way to detect that you're being MITM'd? Yes, a project we're working on called DNSChain prevents MITM attacks for domains that have their info stored in a blockchain. We're maintaining a list of alternatives and how they compare to DNSChain here: https://github.com/okTurtles/dnschain/blob/master/docs/Comparison.md https://github.com/okTurtles/dnschain/blob/master/docs/Compa...
- zaroth 12y ago
  It's the golden unsolved, perhaps unsolvable problem in crypto. Trusting trust and such. There's always a key, somewhere, that has to be shared. One way to hack the system is if you have actual knowledge of the person you are talking to, and you assume some limited amount of tampering which can be done in real-time. For example, if I know the sound of your voice, and we want to agree on a key with no MITM, we can setup an audio channel and speak some code words to each other. Baring an adversary which can in real-time intercept and synthesize my voice convincingly speaking a different code, this is pretty secure. [1] [ZRTP] allows the detection of man-in-the-middle (MiTM) attacks by displaying a short authentication string (SAS) for the users to read and verbally compare over the phone. Another imperfect defense is spreading over time the data that an attacker would have to intercept and modify in order to MITM. That's what Chrome is doing with their pin lists. Now an adversary would have to alter the pinning when Chrome is downloaded. Of course in this very thread we're talking about technology which can do exactly that. E.g. technology which has any hope of preventing data exfiltration, would have an easy time altering Chrome's pin-list. Of course the Chrome binaries are signed, so there's another layer to defeat, etc. etc. So the end result is there are a lot of good technologies to prevent MITM. If you can keep the attacker out once, you can generally be confident your future conversations will be secure as well, since good protocols don't start from scratch each time, but rather "ratchet" new keys from the old as you go. [2] One of the big trade-offs is false positives and privacy. For example, it might be nice if my browser remembered the public key of a site I visit, like HN, and let me know if it changed. Two issues are a naive implementation would also serve as a great tracker for every site I've visited, and how do I know if when I get a warning, it's a real attack and not just an expiring certificate rotating out? Now we would need a way for sites to indicate, by signing with their old key, that indeed they are switching to a new key, and complexity explodes from there. [1] - http://blog.cryptographyengineering.com/2012/11/lets-talk-about-zrtp.html http://blog.cryptographyengineering.com/2012/11/lets-talk-ab... [2] - https://whispersystems.org/blog/advanced-ratcheting/ https://whispersystems.org/blog/advanced-ratcheting/
  - mjs 12y ago
    > It's the golden unsolved, perhaps unsolvable problem in crypto. Sorry, perhaps my question wasn't clear. I wasn't asking about MITM in the general case, I was asking about this particular case. The certificate chain for Hacker News seems to go AddTrust -> COMODO -> Another COMODO -> *.ycombinator.com. So in this case, if you're MITM'd by MCS Holdings, is MCS Holdings going to be part of the chain (after a CNNIC)?
- JeffCyr 12y ago
  For web site with authentication (e.g. bank account), protocols like SRP (Secure Remote Password) would prevent the man-in-the-middle if he doesn't know your password. SRP is a mutual authentication protocol with zero knowledge and forward secrecy, it would be nice if major browsers supported it, it's not usable without browser support.
jsprogrammer 12y ago
> if you are a company that handles confidential medical information (any health care organization, many insurers, every employee benefits management organization, &c), you may be required to have controls in place to ensure that nobody uses your Internet connection to exfiltrate people's PII through Google Mail. Yes, but what are those controls? You check every packet to see if it contains any information from one of your databases? What if the person sending the data just applies a simple obfuscation technique to the data, or just tunnels through some other encryption scheme? Edit: downmods? really?
- acdha 12y ago
  Search for things like “data loss appliance”. As an example, when BlueCoat isn't helping repressive regimes spy on their citizens, they're helping businesses watch every outgoing packet: https://www.bluecoat.com/products/dlp https://www.bluecoat.com/products/dlp “Blue Coat DLP allows you to easily create policies that analyze the data source, content, destination and more. … accurate data “fingerprinting” capabilities, in addition to powerful keyword, pattern, and regular expression support, so you can create precision policies to effectively secure your data while minimizing false positives.” Sure, the every HN reader might have questions about this but I'd bet a LOT of C-level executives are receptive to this.
  - kjs3 12y ago
    What questions do you have? Limiting the scope of discovery to fingerprinted data is a pretty good way to limit "incidental" data filtering/discovery.
    - acdha 12y ago
      Oh, sorry, I meant questions like the ones raised about how someone might try to smuggle data past such filters or some of the security aspects of having a single point with access to everything. I certainly agree that if you have a requirement to watch outbound data like this, having a system to selectively capture it is much better than simply attempting to record everything.
- 12y ago
cesarb 12y ago
What if the site you're accessing is required to have controls in place to ensure that nobody can intercept the communication between the user and the site? I'd expect that to be the case when the site handles things like confidential medical information.
- snowwrestler 12y ago
  When you are using your employer's computing equipment on your employer's premises, you have limited right to privacy.
- kjs3 12y ago
  In a typical deployment of MitM tech (e.g. Bluecoat, Websense, etc.), things like personal banking, health care sites, etc., are exempted from the interception policy to avoid personal privacy issues and HR headaches. This can be overridden in the local policy of course, but I've rarely seen that in practice (anecdote isn't fact, blah, blah). Be aware that the site you're going to may be MitM'ing sessions to meet other compliance regulations (e.g. SOX in the financial sector).
  - cesarb 12y ago
    > In a typical deployment of MitM tech (e.g. Bluecoat, Websense, etc.), things like personal banking, health care sites, etc., are exempted from the interception policy to avoid personal privacy issues and HR headaches. How does it know? Does it have a list of all "personal banking, healthcare sites, etc" from the whole world? How is that list kept up-to-date? What happens if the site the employee is accessing is missing from the list? What happens if the employee knows these sites aren't monitored and finds a way to use them to bypass the monitoring? > Be aware that the site you're going to may be MitM'ing sessions to meet other compliance regulations (e.g. SOX in the financial sector). If it's the site itself, is it really a MITM? And even if they technically use a MITM, does it really matter, since the site would have access to the plaintext anyways?
  - deleted 12y ago
    [deleted]

Stefan-H 12y ago

All of the reasons that benefit the company. Data Loss Prevention, web filtering, malware detection, take your pick.

bradleyjg 12y ago
While there may well be good reasons to MitM HTTPS on a corporate network, the case isn't quite so clear for secretly doing so. IIRC chrome disables altogether certificate pin violation notifications if the offending certificate is locally installed. While it probably is the right move to forgo the giant security warning in that case, I don't see why they can't use an "orange light" type indicator and in the popup explain corporate monitoring (with a further note that if you aren't on an institutional computer you probably have a virus). While corporate IT departments could recompile chromium sans message, or just ban chrome altogether, why make it easy for them?
- Stefan-H 12y ago
  If you are using corporate hardware it should not really be secret that your traffic is being man in the middled, this should be assumed. I think it makes sense for a corporation to be able to whitelist their certificate to make intermediate network devices appear as trusted, because they are. I do agree that having a little asterisk or something for the lock ice to indicate that you are using a certificate that falls outside of the default trust store could be beneficial.
- djrogers 12y ago
  The stuff I work with has the option to pop up a warning/comfort page to explain the practice/policies etc every N hours - seems to be a good thing to use.

Buge 12y ago

One reason would be an Intrusion Detection System: make sure no malware gets downloaded, or to analyze traffic for stuff that looks like malware phoning home. http://en.wikipedia.org/wiki/Intrusion_detection_system http://en.wikipedia.org/wiki/Intrusion_detection_system

MichaelSalib 12y ago

A good friend of mine works for a major electronics manufacturer (trust me, you'd recognize the name) where some employees exfiltrated 200,000 internal design documents/artifacts to a competitor that they were planning on joining. As a result, no one can use gmail/gchat from work machines or VPNs anymore. I think a MITM proxy that detected giant file exfils but allowed people to send gchat messages to their family would be a huge plus in that environment.