5 ms·

China, GitHub and the man-in-the-middle

36 points by moonboots 14y ago

loeg 14y ago
Fwiw, my employer (large East coast USA software firm) also MITMs Github (and the rest of HTTPS, excluding a small whitelist). Their MITM software doesn't even bother to validate the certificates on their side of things, where it is possible. It is … not very awesome.
- kyllo 14y ago
  Is that to discourage employees from working on personal projects at the office, and/or to discourage them from sending company-owned code outside their corporate network?
  - danielweber 14y ago
    More the latter. It's probably impossible to stop all encrypted traffic that you can't look at, but you can make it harder for people to do it by stupid or by malware.
    - snogglethorpe 14y ago
      > and/or to discourage them from sending company-owned code outside their corporate network? > More the latter Sooooooo I guess employees have to resort to the old "micro SD card in your shoe" technique... Or just use a tunneling proxy.
      - loeg 14y ago
        Yes, getting around it is easy. It's just obnoxious, and adds latency, and application support for SOCKS is shitty, and … I guess I could set up OpenVPN on a VPS or something.
    - loeg 14y ago
      OP here. Actually, their logic is that this way they can scan files for viruses (not kidding). (E.g., from gmail attachments.)
      - pnathan 14y ago
        This happens at other employers as well; same general rationale.
- j_s 14y ago
  Just curious what the whitelist is... Chrome's pinned certs? That's always a point of curiosity for me: no one knows what Chrome is sending to Google.
  - moxie 14y ago
    Chrome's pinning logic is disabled for connections where the signing cert was added to the trust store by a user, I think largely in part to avoid breaking these type of corporate MITM proxies. So if you want to watch the traffic, it should be as simple as MITMing yourself with a cert you add to the Chrome trust DB.
    - loeg 14y ago
      I don't want my corp firewall spying on net traffic, so I don't add them to the trusted CAs DB. It would be slightly more palatable if the firewall did cert validation on the other side of things… but they don't.
  - loeg 14y ago
    No, they MITM google as well as everyone else. The whitelist includes yelp, for some reason... not really sure what else. I definitely do not add their MITM CA as a trusted root in my browser...
- deleted 14y ago
  [deleted]
tptacek 14y ago
This is why calls to make click-throughs for self-signed certificates simpler and less scary are misguided.
- fosap 14y ago
  Chains of trust can't defend you from this. Only certificate pinning. IMO this shows why self signed is the way to go: There are no authorities you can trust.
  - tptacek 14y ago
    Self signed is indistinguishable from "China is MITM'ing you". We agree about pinning. As pinning becomes more widespread, browsers that support it will become a sort of surveillance network for forged certificates. That's effectively what caused the Turktrust discovery.
    - lucian1900 14y ago
      It would be different if it worked like ssh, where key changes are warned about after the (optional) leap of faith.
      - patio11 14y ago
        The SSH model for SSL is a non-starter, because you can MITM bankofamerica.com or Gmail for an hour and find tens of thousands of people who just reinstalled Windows, bought a new iPad, etc etc, and they will fall instantly to your MITM attack. (And -- more's the hilarity -- if they try to go back to bankofamerica.com tomorrow it will look like the bank is trying to MITM them.)
        moonboots 14y ago
        The new ssl pinning proposals work very similarly to ssh. When the user visits an https site with pinning enabled, the browser will remember the server's public key similar to ssh's known_hosts. You're correct that this won't protect against a MITM during this first visit and will cause confusion if an attacker pins his fraudulent public key. However, I would argue that pinning provides a large net security gain in practice. The same model of vulnerable initial visit but secure subsequent visits is used in HSTS to prevent ssl stripping attacks.
alxndr 14y ago
tl;dr - "At around 8pm, on January 26, reports appeared on Weibo and Twitter that users in China trying to access GitHub.com were getting warning messages about invalid SSL certificates. The evidence, listed further down in this post, indicates that this was caused by a man-in-the-middle attack." "The attack happened on a Saturday night. It was very crude, in that the fake certificate was signed by an unknown authority and bound to be detected quickly. The attack stopped after about an hour." "While the attack was short-lived, it is possible that passwords of many GitHub users were recorded. It’s also possible that the IP addresses of users accessing certain URLs, such as these lists of GFW [Great Firewall] contributors, were tracked." "HTTPS effectively disables half of what the Great Firewall can do. We have argued for a long time that the reason that Gmail isn’t fully blocked is that it’s considered too important and that the backlash against closing down access would be too great. ... It now appears that GitHub has been added to this list. ... With every website that switches to HTTPS, the authorities’ options are limited to two: completely blocking it, or completely allowing it. The more they fear a public reaction to complete blocks, the fewer their options become. Man-in-the-middle attacks are likely to become increasingly tempting." "No browser would prevent the authorities from using their ultimate tool though: certificates signed by the China Internet Network Information Center. CNNIC is controlled by the government through the Ministry of Industry and Information Technology. They are recognized by all major browsers as a trusted Certificate Authority. If they sign a fake certificate used in a man-in-the-middle attack, no browser will warn of any usual activity."
- loeg 14y ago
  > "No browser would prevent the authorities from using their ultimate tool though: certificates signed by the China Internet Network Information Center. CNNIC is controlled by the government through the Ministry of Industry and Information Technology. They are recognized by all major browsers as a trusted Certificate Authority. If they sign a fake certificate used in a man-in-the-middle attack, no browser will warn of any usual activity." That is the important part. I am surprised China isn't doing this already. Maybe they are doing so, but only for targeted attacks. The CA community really shouldn't grant China any CA authority whatsoever...
  - 14y ago
pjungwir 14y ago
Ironically this site gives me an SSL warning about an unknown certificate issuer.
- tantalor 14y ago
  What browser are you using? No issue for me in Chrome.
  - pjungwir 14y ago
    Firefox 14.0.1 on Ubuntu 12.04.
    - deleted 14y ago
      [deleted]
    - pjungwir 14y ago
      You can run this to get details about the certificate chain: $ SITE=en.greatfire.org $ echo "HEAD / HTTP/1.0\n Host: $SITE:443\n\n EOT\n" | openssl s_client -prexit -connect $SITE:443 I'm not sure how to interpret the results, but I'd be thrilled if someone more knowledgeable would comment. I see there is this chain of certs: Certificate chain 0 s:/OU=Domain Control Validated/OU=PositiveSSL/CN=greatfire.org i:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 1 s:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root i:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root 2 s:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 i:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root and openssl seems to complain about a self-signed certificate: Verify return code: 19 (self signed certificate in certificate chain)
      - tantalor 14y ago
        How do you tell whether it's self signed? There are two certificates so maybe one is not self signed?
dangero 14y ago
Maybe the goal isn't to monitor their people as much as gain admin access passwords to every major open source project? As talked about prior, backdoors in open source seem like a real concern. Even if source code is public for open source projects, how do we know a precompiled binary actually matches the source?
netresec 14y ago
New findings regarding the Chinese MITM of GitHub.com can be found here: http://netresec.com/?b=1328C6B http://netresec.com/?b=1328C6B Turns out the guy who uploaded the packet capture file was @chenshaoju

36 points by moonboots 14y ago

loeg 14y ago

Fwiw, my employer (large East coast USA software firm) also MITMs Github (and the rest of HTTPS, excluding a small whitelist). Their MITM software doesn't even bother to validate the certificates on their side of things, where it is possible. It is … not very awesome.

kyllo 14y ago
Is that to discourage employees from working on personal projects at the office, and/or to discourage them from sending company-owned code outside their corporate network?
- danielweber 14y ago
  More the latter. It's probably impossible to stop all encrypted traffic that you can't look at, but you can make it harder for people to do it by stupid or by malware.
  - snogglethorpe 14y ago
    > and/or to discourage them from sending company-owned code outside their corporate network? > More the latter Sooooooo I guess employees have to resort to the old "micro SD card in your shoe" technique... Or just use a tunneling proxy.
    - loeg 14y ago
      Yes, getting around it is easy. It's just obnoxious, and adds latency, and application support for SOCKS is shitty, and … I guess I could set up OpenVPN on a VPS or something.
  - loeg 14y ago
    OP here. Actually, their logic is that this way they can scan files for viruses (not kidding). (E.g., from gmail attachments.)
    - pnathan 14y ago
      This happens at other employers as well; same general rationale.
j_s 14y ago
Just curious what the whitelist is... Chrome's pinned certs? That's always a point of curiosity for me: no one knows what Chrome is sending to Google.
- moxie 14y ago
  Chrome's pinning logic is disabled for connections where the signing cert was added to the trust store by a user, I think largely in part to avoid breaking these type of corporate MITM proxies. So if you want to watch the traffic, it should be as simple as MITMing yourself with a cert you add to the Chrome trust DB.
  - loeg 14y ago
    I don't want my corp firewall spying on net traffic, so I don't add them to the trusted CAs DB. It would be slightly more palatable if the firewall did cert validation on the other side of things… but they don't.
- loeg 14y ago
  No, they MITM google as well as everyone else. The whitelist includes yelp, for some reason... not really sure what else. I definitely do not add their MITM CA as a trusted root in my browser...
deleted 14y ago
[deleted]

tptacek 14y ago

This is why calls to make click-throughs for self-signed certificates simpler and less scary are misguided.

fosap 14y ago
Chains of trust can't defend you from this. Only certificate pinning. IMO this shows why self signed is the way to go: There are no authorities you can trust.
- tptacek 14y ago
  Self signed is indistinguishable from "China is MITM'ing you". We agree about pinning. As pinning becomes more widespread, browsers that support it will become a sort of surveillance network for forged certificates. That's effectively what caused the Turktrust discovery.
  - lucian1900 14y ago
    It would be different if it worked like ssh, where key changes are warned about after the (optional) leap of faith.
    - patio11 14y ago
      The SSH model for SSL is a non-starter, because you can MITM bankofamerica.com or Gmail for an hour and find tens of thousands of people who just reinstalled Windows, bought a new iPad, etc etc, and they will fall instantly to your MITM attack. (And -- more's the hilarity -- if they try to go back to bankofamerica.com tomorrow it will look like the bank is trying to MITM them.)
      - moonboots 14y ago
        The new ssl pinning proposals work very similarly to ssh. When the user visits an https site with pinning enabled, the browser will remember the server's public key similar to ssh's known_hosts. You're correct that this won't protect against a MITM during this first visit and will cause confusion if an attacker pins his fraudulent public key. However, I would argue that pinning provides a large net security gain in practice. The same model of vulnerable initial visit but secure subsequent visits is used in HSTS to prevent ssl stripping attacks.

alxndr 14y ago

tl;dr - "At around 8pm, on January 26, reports appeared on Weibo and Twitter that users in China trying to access GitHub.com were getting warning messages about invalid SSL certificates. The evidence, listed further down in this post, indicates that this was caused by a man-in-the-middle attack." "The attack happened on a Saturday night. It was very crude, in that the fake certificate was signed by an unknown authority and bound to be detected quickly. The attack stopped after about an hour." "While the attack was short-lived, it is possible that passwords of many GitHub users were recorded. It’s also possible that the IP addresses of users accessing certain URLs, such as these lists of GFW [Great Firewall] contributors, were tracked." "HTTPS effectively disables half of what the Great Firewall can do. We have argued for a long time that the reason that Gmail isn’t fully blocked is that it’s considered too important and that the backlash against closing down access would be too great. ... It now appears that GitHub has been added to this list. ... With every website that switches to HTTPS, the authorities’ options are limited to two: completely blocking it, or completely allowing it. The more they fear a public reaction to complete blocks, the fewer their options become. Man-in-the-middle attacks are likely to become increasingly tempting." "No browser would prevent the authorities from using their ultimate tool though: certificates signed by the China Internet Network Information Center. CNNIC is controlled by the government through the Ministry of Industry and Information Technology. They are recognized by all major browsers as a trusted Certificate Authority. If they sign a fake certificate used in a man-in-the-middle attack, no browser will warn of any usual activity."

loeg 14y ago
> "No browser would prevent the authorities from using their ultimate tool though: certificates signed by the China Internet Network Information Center. CNNIC is controlled by the government through the Ministry of Industry and Information Technology. They are recognized by all major browsers as a trusted Certificate Authority. If they sign a fake certificate used in a man-in-the-middle attack, no browser will warn of any usual activity." That is the important part. I am surprised China isn't doing this already. Maybe they are doing so, but only for targeted attacks. The CA community really shouldn't grant China any CA authority whatsoever...
- 14y ago

pjungwir 14y ago

Ironically this site gives me an SSL warning about an unknown certificate issuer.

tantalor 14y ago
What browser are you using? No issue for me in Chrome.
- pjungwir 14y ago
  Firefox 14.0.1 on Ubuntu 12.04.
  - deleted 14y ago
    [deleted]
  - pjungwir 14y ago
    You can run this to get details about the certificate chain: $ SITE=en.greatfire.org $ echo "HEAD / HTTP/1.0\n Host: $SITE:443\n\n EOT\n" | openssl s_client -prexit -connect $SITE:443 I'm not sure how to interpret the results, but I'd be thrilled if someone more knowledgeable would comment. I see there is this chain of certs: Certificate chain 0 s:/OU=Domain Control Validated/OU=PositiveSSL/CN=greatfire.org i:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 1 s:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root i:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root 2 s:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 i:/C=SE/O=AddTrust AB/OU=AddTrust External TTP Network/CN=AddTrust External CA Root and openssl seems to complain about a self-signed certificate: Verify return code: 19 (self signed certificate in certificate chain)
    - tantalor 14y ago
      How do you tell whether it's self signed? There are two certificates so maybe one is not self signed?

dangero 14y ago

Maybe the goal isn't to monitor their people as much as gain admin access passwords to every major open source project? As talked about prior, backdoors in open source seem like a real concern. Even if source code is public for open source projects, how do we know a precompiled binary actually matches the source?

netresec 14y ago

New findings regarding the Chinese MITM of GitHub.com can be found here: http://netresec.com/?b=1328C6B http://netresec.com/?b=1328C6B Turns out the guy who uploaded the packet capture file was @chenshaoju