Ryan Sleevi
2017-03-23 16:02:35 UTC
Note: Historically, the Google Chrome team has not used the Blink Process
<http://www.chromium.org/blink#new-features> for Certificate
Authority-related security issues, of which there have been a number over
the years. However, we are interested in exploring using this process for
such changes, as it provides a greater degree of transparency and public
participation. Based on the level of participation and feedback we receive,
we may consider using this for the future. However, as CA-related security
incidents may require immediate response to protect users, this should not
be seen as a guarantee that this process can be used in future incident
responses.
Primary eng (and PM) emails:
***@chromium.org ***@chromium.org
Summary
Since January 19, the Google Chrome team has been investigating a series of
failures by Symantec Corporation to properly validate certificates. Over
the course of this investigation, the explanations provided by Symantec
have revealed a continually increasing scope of misissuance with each set
of questions from members of the Google Chrome team; an initial set of
reportedly 127 certificates has expanded to include at least 30,000
certificates, issued over a period spanning several years. This is also
coupled with a series of failures following the previous set of misissued
certificates from Symantec
<https://security.googleblog.com/2015/10/sustaining-digital-certificate-security.html>,
causing us to no longer have confidence in the certificate issuance
policies and practices of Symantec over the past several years. To restore
confidence and security of our users, we propose the following steps:
-
A reduction in the accepted validity period of newly issued
Symantec-issued certificates to nine months or less, in order to minimize
any impact to Google Chrome users from any further misissuances that may
arise.
-
An incremental distrust, spanning a series of Google Chrome releases, of
all currently-trusted Symantec-issued certificates, requiring they be
revalidated and replaced.
-
Removal of recognition of the Extended Validation status of Symantec
issued certificates, until such a time as the community can be assured in
the policies and practices of Symantec, but no sooner than one year.
Motivation
As captured in Chromeâs Root Certificate Policy
<https://www.chromium.org/Home/chromium-security/root-ca-policy>, root
certificate authorities are expected to perform a number of critical
functions commensurate with the trust granted to them. This includes
properly ensuring that domain control validation is performed for server
certificates, to audit logs frequently for evidence of unauthorized
issuance, and to protect their infrastructure in order to minimize the
ability for the issuance of fraudulent certs.
On the basis of the details publicly provided by Symantec, we do not
believe that they have properly upheld these principles, and as such, have
created significant risk for Google Chrome users. Symantec allowed at least
four parties access to their infrastructure in a way to cause certificate
issuance, did not sufficiently oversee these capabilities as required and
expected, and when presented with evidence of these organizationsâ failure
to abide to the appropriate standard of care, failed to disclose such
information in a timely manner or to identify the significance of the
issues reported to them.
These issues, and the corresponding failure of appropriate oversight,
spanned a period of several years, and were trivially identifiable from the
information publicly available or that Symantec shared.
The full disclosure of these issues has taken more than a month. Symantec
has failed to provide timely updates to the community regarding these
issues. Despite having knowledge of these issues, Symantec has repeatedly
failed to proactively disclose them. Further, even after issues have
become public, Symantec failed to provide the information that the
community required to assess the significance of these issues until they
had been specifically questioned. The proposed remediation steps offered by
Symantec have involved relying on known-problematic information or using
practices insufficient to provide the level of assurance required under the
Baseline Requirements and expected by the Chrome Root CA Policy.
In January 2015, Symantec-issued certificates represented more than 30% of
the valid certificates by volume. While changes in the CA ecosystem have
seen that share decrease over the past two years, there is still a
significant compatibility risk for an immediate and complete distrust.
Further, due to overall TLS ecosystem concerns, we understand that it may
take non-trivial effort for some site operators to find suitable solutions,
as the need to support older devices may necessitate the use of particular
CAs, meaning that distrust of new certificates also has significant
compatibility risk.
To balance the compatibility risks versus the security risks, we propose a
gradual distrust of all existing Symantec-issued certificates, requiring
that they be replaced over time with new, fully revalidated certificates,
compliant with the current Baseline Requirements. This will be accomplished
by gradually decreasing the âmaximum ageâ of Symantec-issued certificates
over a series of releases, distrusting certificates whose validity period
(the difference of notBefore to notAfter) exceeds the specified maximum.
The proposed schedule is as follows:
Chrome 59 (Dev, Beta, Stable): 33 months validity (1023 days)
Chrome 60 (Dev, Beta, Stable): 27 months validity (837 days)
Chrome 61 (Dev, Beta, Stable): 21 months validity (651 days)
Chrome 62 (Dev, Beta, Stable): 15 months validity (465 days)
Chrome 63 (Dev, Beta): 9 months validity (279 days)
Chrome 63 (Stable): 15 months validity (465 days)
Chrome 64 (Dev, Beta, Stable): 9 months validity (279 days)
The proposed schedule attempts to avoid making changes in Chrome 63 Stable,
as that would be released during the winter holiday production freeze many
organizations undergo. This is solely to reduce disruption for site
operators and users, and attempts to resume with Chrome 64 following the
holiday season. Further, the practical impact of the changes in Chrome 59
and 60 are relatively minimal, due to many of the certificates issued
during that period of time being issued using SHA-1, which is no longer
supported for certificates in Chrome.
In addition, we propose to require that all newly-issued certificates must
have validity periods of no greater than 9 months (279 days) in order to be
trusted in Google Chrome, effective Chrome 61. This ensures that the risk
of any further misissuance is, at most, limited to nine months, and more
importantly, that if any further action is warranted or necessary, that the
entire ecosystem can migrate within that time period, thus minimizing the
risk of further compatibility issues.
By combining these two steps, we can ensure that the level of assurance in
Symantec-issued certificates is able to match what is expected by Google
Chrome and the ecosystem, and that the risks posed both from past and
possible future misissuance is minimized as much as possible.
Given the nature of these issues, and the multiple failures of Symantec to
ensure that the level of assurance provided by their certificates meets the
requirements of the Baseline Requirements or Extended Validation
Guidelines, we no longer have the confidence necessary in order to grant
Symantec-issued certificates the âExtended Validationâ status. As
documented with both the current and past misissuance, Symantec failed to
ensure that the organizational attributes, displayed within the address bar
for such certificates, meet the level of quality and validation required
for such display. Therefore, we propose to remove such indicators,
effective immediately, until Symantec is able to demonstrate the level of
sustained compliance necessary to grant such trust, which will be a period
no less than a year. After such time has passed, we will consider requests
from Symantec to re-evaluate this position, in collaboration with the
broader Chromium community.
Compatibility and Interoperability Risk
As with any reduction in trust in a Certificate Authority, this poses a
non-trivial degree of compatibility risk. This is because site operators
desire to have their certificates recognized in all client browsers, and if
one or more browsers fail to trust a given CA, this is prevented from
happening.
On the other hand, all site operators expect that certificates will only be
issued for their domains upon their request, and the failure to have that
assurance significantly undermines the security of HTTPS for both site
operators and users.
This compatibility risk is especially high for Symantec-issued
certificates, due to their acquisition of some of the first CAs, such as
Thawte, Verisign, and Equifax, which are some of the most widely supported
CAs. Distrusting such CAs creates further difficulty for providing secure
connections to both old and new devices alike, due to the need to ensure
the CA a site operator uses is recognized across these devices.
Further, the immediate distrust of a CA, as has been necessary in the past,
can significantly impact both site operators and users. Site operators are
forced to acquire certificates from other CAs, without having the
opportunity and time to research which CAs best meet their needs, and users
encounter a substantial number of errors until those site operators act,
conditioning them to ignore security warnings. In the event that only a
single browser distrusts such a CA, the error is often seen as the
browserâs fault, despite it being a failure of the CA to provide the
necessary level of assurance, and the site operator to respond in a timely
fashion.
Assessing the compatibility risk with both Edge and Safari is difficult,
because neither Microsoft nor Apple communicate publicly about their
changes in trust prior to enacting them.
While Mozilla conducts their discussions regarding Certificate Authorities
in public, and were the first to be alerted of these latest issues, they
have not yet begun discussion of the next steps to how best to protect
their users. Our hope is that this proposal may be seen as one that
appropriately balances the security and compatibility risks with the needs
of site operators, browsers, and users, and we welcome all feedback.
Alternative implementation suggestion for web developers
This proposal allows for web developers to continue to use Symantec issued
certificates, but will see their validity period reduced. This ensure that
web developers are aware of the risk and potential of future distrust of
Symantec-issued certificates, should additional misissuance events occur,
while also allowing them the flexibility to continue using such
certificates should it be necessary.
Usage information from UseCounter
<https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/page/UseCounter.h&sq=package:chromium&type=cs&q=file:UseCounter.h%20Feature&l=39>
:
For a variety of non-technical reasons, we do not currently instrument the
usage of CAs. Further, few public metrics exist for intersecting usage
information with the validity period, since only certificates valid greater
than nine months will be affected outside of their normal replacement
cycle. From Mozilla Firefoxâs Telemetry, we know that Symantec issued
certificates are responsible for 42% of certificate validations. However,
this number is not strictly an indicator for impact, as this number is
biased towards counting certificates for heavily-trafficked sites, and
whose issuance is fully automated and/or whose validity periods will be
unaffected, thus significantly overstating impact. By phasing such changes
in over a series of releases, we aim to minimize the impact any given
release poses, while still continually making progress towards restoring
the necessary level of security to ensure Symantec issued certificates are
as trustworthy as certificates from other CAs.
<http://www.chromium.org/blink#new-features> for Certificate
Authority-related security issues, of which there have been a number over
the years. However, we are interested in exploring using this process for
such changes, as it provides a greater degree of transparency and public
participation. Based on the level of participation and feedback we receive,
we may consider using this for the future. However, as CA-related security
incidents may require immediate response to protect users, this should not
be seen as a guarantee that this process can be used in future incident
responses.
Primary eng (and PM) emails:
***@chromium.org ***@chromium.org
Summary
Since January 19, the Google Chrome team has been investigating a series of
failures by Symantec Corporation to properly validate certificates. Over
the course of this investigation, the explanations provided by Symantec
have revealed a continually increasing scope of misissuance with each set
of questions from members of the Google Chrome team; an initial set of
reportedly 127 certificates has expanded to include at least 30,000
certificates, issued over a period spanning several years. This is also
coupled with a series of failures following the previous set of misissued
certificates from Symantec
<https://security.googleblog.com/2015/10/sustaining-digital-certificate-security.html>,
causing us to no longer have confidence in the certificate issuance
policies and practices of Symantec over the past several years. To restore
confidence and security of our users, we propose the following steps:
-
A reduction in the accepted validity period of newly issued
Symantec-issued certificates to nine months or less, in order to minimize
any impact to Google Chrome users from any further misissuances that may
arise.
-
An incremental distrust, spanning a series of Google Chrome releases, of
all currently-trusted Symantec-issued certificates, requiring they be
revalidated and replaced.
-
Removal of recognition of the Extended Validation status of Symantec
issued certificates, until such a time as the community can be assured in
the policies and practices of Symantec, but no sooner than one year.
Motivation
As captured in Chromeâs Root Certificate Policy
<https://www.chromium.org/Home/chromium-security/root-ca-policy>, root
certificate authorities are expected to perform a number of critical
functions commensurate with the trust granted to them. This includes
properly ensuring that domain control validation is performed for server
certificates, to audit logs frequently for evidence of unauthorized
issuance, and to protect their infrastructure in order to minimize the
ability for the issuance of fraudulent certs.
On the basis of the details publicly provided by Symantec, we do not
believe that they have properly upheld these principles, and as such, have
created significant risk for Google Chrome users. Symantec allowed at least
four parties access to their infrastructure in a way to cause certificate
issuance, did not sufficiently oversee these capabilities as required and
expected, and when presented with evidence of these organizationsâ failure
to abide to the appropriate standard of care, failed to disclose such
information in a timely manner or to identify the significance of the
issues reported to them.
These issues, and the corresponding failure of appropriate oversight,
spanned a period of several years, and were trivially identifiable from the
information publicly available or that Symantec shared.
The full disclosure of these issues has taken more than a month. Symantec
has failed to provide timely updates to the community regarding these
issues. Despite having knowledge of these issues, Symantec has repeatedly
failed to proactively disclose them. Further, even after issues have
become public, Symantec failed to provide the information that the
community required to assess the significance of these issues until they
had been specifically questioned. The proposed remediation steps offered by
Symantec have involved relying on known-problematic information or using
practices insufficient to provide the level of assurance required under the
Baseline Requirements and expected by the Chrome Root CA Policy.
In January 2015, Symantec-issued certificates represented more than 30% of
the valid certificates by volume. While changes in the CA ecosystem have
seen that share decrease over the past two years, there is still a
significant compatibility risk for an immediate and complete distrust.
Further, due to overall TLS ecosystem concerns, we understand that it may
take non-trivial effort for some site operators to find suitable solutions,
as the need to support older devices may necessitate the use of particular
CAs, meaning that distrust of new certificates also has significant
compatibility risk.
To balance the compatibility risks versus the security risks, we propose a
gradual distrust of all existing Symantec-issued certificates, requiring
that they be replaced over time with new, fully revalidated certificates,
compliant with the current Baseline Requirements. This will be accomplished
by gradually decreasing the âmaximum ageâ of Symantec-issued certificates
over a series of releases, distrusting certificates whose validity period
(the difference of notBefore to notAfter) exceeds the specified maximum.
The proposed schedule is as follows:
Chrome 59 (Dev, Beta, Stable): 33 months validity (1023 days)
Chrome 60 (Dev, Beta, Stable): 27 months validity (837 days)
Chrome 61 (Dev, Beta, Stable): 21 months validity (651 days)
Chrome 62 (Dev, Beta, Stable): 15 months validity (465 days)
Chrome 63 (Dev, Beta): 9 months validity (279 days)
Chrome 63 (Stable): 15 months validity (465 days)
Chrome 64 (Dev, Beta, Stable): 9 months validity (279 days)
The proposed schedule attempts to avoid making changes in Chrome 63 Stable,
as that would be released during the winter holiday production freeze many
organizations undergo. This is solely to reduce disruption for site
operators and users, and attempts to resume with Chrome 64 following the
holiday season. Further, the practical impact of the changes in Chrome 59
and 60 are relatively minimal, due to many of the certificates issued
during that period of time being issued using SHA-1, which is no longer
supported for certificates in Chrome.
In addition, we propose to require that all newly-issued certificates must
have validity periods of no greater than 9 months (279 days) in order to be
trusted in Google Chrome, effective Chrome 61. This ensures that the risk
of any further misissuance is, at most, limited to nine months, and more
importantly, that if any further action is warranted or necessary, that the
entire ecosystem can migrate within that time period, thus minimizing the
risk of further compatibility issues.
By combining these two steps, we can ensure that the level of assurance in
Symantec-issued certificates is able to match what is expected by Google
Chrome and the ecosystem, and that the risks posed both from past and
possible future misissuance is minimized as much as possible.
Given the nature of these issues, and the multiple failures of Symantec to
ensure that the level of assurance provided by their certificates meets the
requirements of the Baseline Requirements or Extended Validation
Guidelines, we no longer have the confidence necessary in order to grant
Symantec-issued certificates the âExtended Validationâ status. As
documented with both the current and past misissuance, Symantec failed to
ensure that the organizational attributes, displayed within the address bar
for such certificates, meet the level of quality and validation required
for such display. Therefore, we propose to remove such indicators,
effective immediately, until Symantec is able to demonstrate the level of
sustained compliance necessary to grant such trust, which will be a period
no less than a year. After such time has passed, we will consider requests
from Symantec to re-evaluate this position, in collaboration with the
broader Chromium community.
Compatibility and Interoperability Risk
As with any reduction in trust in a Certificate Authority, this poses a
non-trivial degree of compatibility risk. This is because site operators
desire to have their certificates recognized in all client browsers, and if
one or more browsers fail to trust a given CA, this is prevented from
happening.
On the other hand, all site operators expect that certificates will only be
issued for their domains upon their request, and the failure to have that
assurance significantly undermines the security of HTTPS for both site
operators and users.
This compatibility risk is especially high for Symantec-issued
certificates, due to their acquisition of some of the first CAs, such as
Thawte, Verisign, and Equifax, which are some of the most widely supported
CAs. Distrusting such CAs creates further difficulty for providing secure
connections to both old and new devices alike, due to the need to ensure
the CA a site operator uses is recognized across these devices.
Further, the immediate distrust of a CA, as has been necessary in the past,
can significantly impact both site operators and users. Site operators are
forced to acquire certificates from other CAs, without having the
opportunity and time to research which CAs best meet their needs, and users
encounter a substantial number of errors until those site operators act,
conditioning them to ignore security warnings. In the event that only a
single browser distrusts such a CA, the error is often seen as the
browserâs fault, despite it being a failure of the CA to provide the
necessary level of assurance, and the site operator to respond in a timely
fashion.
Assessing the compatibility risk with both Edge and Safari is difficult,
because neither Microsoft nor Apple communicate publicly about their
changes in trust prior to enacting them.
While Mozilla conducts their discussions regarding Certificate Authorities
in public, and were the first to be alerted of these latest issues, they
have not yet begun discussion of the next steps to how best to protect
their users. Our hope is that this proposal may be seen as one that
appropriately balances the security and compatibility risks with the needs
of site operators, browsers, and users, and we welcome all feedback.
Alternative implementation suggestion for web developers
This proposal allows for web developers to continue to use Symantec issued
certificates, but will see their validity period reduced. This ensure that
web developers are aware of the risk and potential of future distrust of
Symantec-issued certificates, should additional misissuance events occur,
while also allowing them the flexibility to continue using such
certificates should it be necessary.
Usage information from UseCounter
<https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/page/UseCounter.h&sq=package:chromium&type=cs&q=file:UseCounter.h%20Feature&l=39>
:
For a variety of non-technical reasons, we do not currently instrument the
usage of CAs. Further, few public metrics exist for intersecting usage
information with the validity period, since only certificates valid greater
than nine months will be affected outside of their normal replacement
cycle. From Mozilla Firefoxâs Telemetry, we know that Symantec issued
certificates are responsible for 42% of certificate validations. However,
this number is not strictly an indicator for impact, as this number is
biased towards counting certificates for heavily-trafficked sites, and
whose issuance is fully automated and/or whose validity periods will be
unaffected, thus significantly overstating impact. By phasing such changes
in over a series of releases, we aim to minimize the impact any given
release poses, while still continually making progress towards restoring
the necessary level of security to ensure Symantec issued certificates are
as trustworthy as certificates from other CAs.
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