Enhancing Download Protection in Firefox

Protection against malicious downloads was added in Firefox 31 on Windows and in Firefox 39 on Mac and Linux. Thanks to Google’s expansion of their Safe Browsing service, Firefox 48 now extends our existing protection to include two additional kinds of downloads: potentially unwanted software and uncommon downloads.

Expanded protection

The first new category, potentially unwanted software, is meant to flag software that makes unexpected changes to your computer, as explained in the Google policy. It is usually best to avoid this kind of software since it could (for example) collect your personal information without your consent and use techniques to make it difficult to uninstall.

The second category, uncommon downloads, covers downloads which may not be malicious or unwanted but that are simply not commonly downloaded. The purpose of this warning is to draw users’ attention to the fact that this may not be the download they think it is. For example, if you are looking to download a new version of Firefox or a popular software package such as VLC and get this warning, it is possible that you have been tricked into downloading a malicious file from a phishing site which has not yet been identified as such by the Google Safe Browsing service. You may want to double-check the address of the site where you downloaded this file and proceed with caution.

Improved user interface

In addition to the new categories described above, we have made improvements to the user interface to make it easier for users to notice and understand these warnings.

Here is what the download button now looks like when a download has been flagged by download protection:

Yellow exclamation mark

Potentially unwanted or uncommon downloads

Red exclamation mark

Malicious downloads

Depending on the category, the default action button will be either “open” or “remove”:

Door hanger with yellow triangle and open button

Potentially unwanted downloads

Door hanger with blue "i" and open button

Uncommon downloads

Door hanger with red "x" and close button

Malicious downloads

and the following confirmation dialog was added to help users understand the risks involved:

Confirmation dialog box defaulting to "Remove file"

Potentially unwanted downloads

Confirmation dialog box defaulting to "Open"

Uncommon downloads

Confirmation dialog box defaulting to "Cancel"

Malicious downloads

We have retained the ability for users to override all of these warnings via the contextual menu if they are convinced that the warning is erroneous:

Menu with "Allow Download" selected using the mouse

Contextual menu

More control for users

The security options in Firefox had remained the same since browsing protection was first introduced in Firefox 3. This is what they looked like in Firefox 47:

Security options showing two Safe Browsing options

Security options prior to Firefox 48

and this is how they changed in Firefox 48 to give users more control around download and browsing protection:

Security options showing three Safe Browsing options

Security options in Firefox 48

While we believe that the vast majority of our users will prefer to keep all of the protections that Safe Browsing offers, we understand that some users may choose to disable parts of the Safe Browsing service based on the privacy guarantees they offer. Our new options aim to give concerned users the necessary level of control and to enable them to retain as much of the Safe Browsing service as they are comfortable with.

Here are what the new options mean:

  • Block dangerous and deceptive content: This enables warnings when visiting pages which contain malware or deceptive content. It is required by the rest of the Safe Browsing functionality.
  • Block dangerous downloads: This enables the download protection feature which may use a remote server to detect malicious executable files.
  • Warn me about unwanted and uncommon software: This extends the download protection feature to also warn about potentially unwanted and uncommon downloads.

Expert users are always welcome to explore (at their own risk) the additional internal configuration settings which are not exposed through the user interface.

March 2016 CA Communication

Mozilla has sent a Communication to the Certification Authorities (CAs) who have root certificates included in Mozilla’s program. Mozilla’s CA Certificate Program governs inclusion of root certificates in Network Security Services (NSS), a set of open source libraries designed to support cross-platform development of security-enabled client and server applications. The NSS root certificate store is not only used in Mozilla products such as the Firefox browser, but is also used by other companies and open-source projects in a variety of applications.

The CA Communication has been emailed to the Primary Point of Contact (POC) for each CA in Mozilla’s program, and they have been asked to respond to 7 action items:

  1. Update us on their progress in eliminating use of SHA-1 as a certificate signature algorithm;
  2. Enter intermediate certificate data into the CA Community in Salesforce;
  3. Enter revoked intermediate certificate data into the CA Community in Salesforce;
  4. Stop issuing certificates with the problems listed here, because we are going to remove the workarounds from mozilla::pkix;
  5. Tell us their plans for removing root certificates that they have retired or are migrating their customers away from;
  6. Confirm their understanding that all certificates, including test certificates, must conform to Mozilla’s stated policies; and
  7. Update us on changes involving transfer of ownership of root certificates, according to our Root Transfer Policy.

The full action items can be read here. Responses to the survey will be automatically and immediately published using Salesforce.

With this CA Communication, we re-iterate that participation in Mozilla’s CA Certificate Program is at our sole discretion, and we will take whatever steps are necessary to keep our users safe. Nevertheless, we believe that the best approach to safeguard that security is to work with CAs as partners, to foster open and frank communication, and to be diligent in looking for ways to improve.

Payment Processors Still Using Weak Crypto

Part of how Mozilla protects the Web is by participating in the governance of the Web PKI, the system of security certificates that allows websites to authenticate themselves to browsers. Together with the other browsers and stakeholders in the Web, we agree on standards for how such certificates are issued.  We then require that these standards, plus a few additional ones specific to Mozilla, be applied to all certificates which are issued, directly or indirectly, by the “roots” that Firefox trusts.

We have been notified that some payment providers are using Web PKI certificates (i.e. certificates which chain up to roots trusted by Firefox) to secure the connection between central servers and payment terminals, for the purpose of transmitting payment data over the public Internet. Unfortunately, some of those non-browser users of the Web PKI have not kept up with the advances in security that the Web is achieving. The SHA-1 hash algorithm (used to validate the integrity of a certificate) has been declared obsolete in the Web PKI, but these providers have failed to upgrade these devices to support its replacement, SHA-2, despite the SHA-1 deadlines having been set years ago. As a result, many payment-related devices continue to require their servers to have certificates which use SHA-1 in order to be able to operate.

In particular, Worldpay PLC approached Mozilla through their Certificate Authority, Symantec, to request authorization to issue, in violation of standard policy, a limited number of SHA-1 certificates needed to support a large number of outdated devices. They made this request less than two weeks before the authorization needed to be effective. To avoid disruption for users of these devices, after a discussion on the dev.security.policy mailing list, in this particular case we have decided to allow these certificates to be issued, but only under a set of conditions that ensure that the issuance of SHA-1 certificates is fully transparent and allowed only for purposes of transition to SHA-2.

This authorization means that Symantec can issue SHA-1 certificates that will enable Worldpay’s devices to keep operating a while longer, and that issuance will not be regarded by Mozilla as a defect. This decision only affects the Mozilla root program; other root programs may still consider the issuance of these certificates to be a mis-issuance.

We understand that there are payment processing organizations other than Worldpay that continue to have similar requirements for SHA-1 — either within the Web PKI or outside it. It is disappointing that these organizations are putting the public’s data at risk by using a weak, outdated security technology.  We encourage organizations with a continuing need for SHA-1 in the Web PKI to come forward as soon as possible and provide as much detail as possible about their plans for a transition to SHA-2.

Mozilla Winter of Security-2015 MozDef: Virtual Reality Interface

Mozilla runs Winter of Security (MWoS) every year to give folks an opportunity to contribute to ongoing security projects in flight. This year an ambitious group took on the task of creating a new visual interface in our SIEM overlay for Elastic  Search that we call MozDef: The Mozilla Defense Platform.

Security personnel are in high demand and analyst skill sets are difficult to maintain. Rather than only focusing on making people better at security, I’m a firm believer that we need to make security better at people. Interfaces that are easier to comprehend and use seem to be a worthwhile investment in that effort and I’m thrilled with the work this team has done.

They’ve wrapped up their project with a great demo of their work. If you are interested in security automation tools and alternative user interfaces, take a couple minutes and check out their work over at air mozilla.


Man-in-the-Middle Interfering with Increased Security

According to the plan we published earlier for deprecating SHA-1, on January 1, 2016, Firefox 43 began rejecting new certificates signed with the SHA-1 digest algorithm.  For Firefox users with unfiltered access to the Internet, this change probably went unnoticed, since there simply aren’t that many new SHA-1 certs being used.  However, for Firefox users who are behind certain “man-in-the-middle” devices (including some security scanners and antivirus products), this change removed their ability to access HTTPS web sites.  When a user tries to connect to an HTTPS site, the man-in-the-middle device sends Firefox a new SHA-1 certificate instead of the server’s real certificate.  Since Firefox rejects new SHA-1 certificates, it can’t connect to the server.

How to tell if you’re affected

If you can access this article in Firefox, you’re fine.  If you’re reading this in another browser, see if you can load the security blog (or any other HTTPS link) in Firefox.  Click “Advanced”, and if you see the error code “SEC_ERROR_CERT_SIGNATURE_ALGORITHM_DISABLED”, then you’re affected.

What to do if you’re affected

The easiest thing to do is to install the newest version of Firefox.  You will need to do this manually, using an unaffected copy of Firefox or a different browser, since we only provide Firefox updates over HTTPS.

If you want to avoid reinstalling, advanced users can fix their local copy of Firefox by going to about:config and changing the value of “security.pki.sha1_enforcement_level” to 0 (which will accept all SHA-1 certificates).

You should also make sure that any systems you have that might be doing man-in-the-middle are up to date, for example, some anti-virus software or security scanning devices.  Some vendors have removed the use of SHA-1 in recent updates.

Commitment to deprecate SHA-1

We are still committed to removing support for SHA-1 certificates from Firefox.  The latest version of Firefox re-enables support for SHA-1 certificates to ensure that we can get updates to users behind man-in-the-middle devices, and enable us to better evaluate how many users might be affected.  Vendors of TLS man-in-the-middle systems should be working to update their products to use newer digest algorithms.

Improving Revocation: OCSP Must-Staple and Short-lived Certificates

Last year, we laid out a long-range plan for improving revocation support for Firefox. As of this week, we’ve completed most of the major elements of that plan. After adding OneCRL earlier this year, we have recently added support for OCSP Must-Staple and short-lived certificates. Together, these changes enable website owners several ways to achieve fast, secure certificate revocation.

In an ideal world, the browser would perform an online status check (such as OCSP) whenever it verifies a certificate, and reject the certificate if the check failed. However, these checks can be slow and unreliable. They time out about 15% of the time, and take about 350ms even when they succeed. Browsers generally soft-fail on revocation in an attempt to balance these concerns.

To get back to stronger revocation checking, we have added support for short-lived certificates and Must-Staple to let sites opt in to hard failures. As of Firefox 41, Firefox will not do “live” OCSP queries for sufficiently short-lived certs (with a lifetime shorter than the value set in “security.pki.cert_short_lifetime_in_days”). Instead, Firefox will just assume the certificate is valid. There is currently no default threshold set, so users need to configure it. We are collecting telemetry on certificate lifetimes, and expect to set the threshold somewhere around the maximum OCSP response lifetime specfied in the baseline requirements.

OCSP Must-Staple makes use of the recently specified TLS Feature Extension. When a CA adds this extension to a certificate, it requires your browser to ensure a stapled OCSP response is present in the TLS handshake. If an OCSP response is not present, the connection will fail and Firefox will display a non-overridable error page. This feature will be included in Firefox 45, currently scheduled to be released in March 2016.

Updated Firefox Security Indicators

This article has been coauthored by Aislinn Grigas, Senior Interaction Designer, Firefox Desktop

Over the past few months, Mozilla has been improving the user experience of our privacy and security features in Firefox. One specific initiative has focused on the feedback shown in our address bar around a site’s security. The major changes are highlighted below along with the rationale behind each change.

Change to DV Certificate treatment in the address bar

Color and iconography is commonly used today to communicate to users when a site is secure. The most widely used patterns are coloring a lock icon and parts of the address bar green. This treatment has a straightforward rationale given green = good in most cultures. Firefox has historically used two different color treatments for the lock icon – a gray lock for Domain-validated (DV) certificates and a green lock for Extended Validation (EV) certificates. The average user is likely not going to understand this color distinction between EV and DV certificates. The overarching message we want users to take from both certificate states is that their connection to the site is secure. We’re therefore updating the color of the lock when a DV certificate is used to match that of an EV certificate.

Although the same green icon will be used, the UI for a site using EV certificates will continue to differ from a site using a DV certificate. Specifically, EV certificates are used when Certificate Authorities (CA) verify the owner of a domain. Hence, we will continue to include the organization name verified by the CA in the address bar.

Changes to Mixed Content Blocker UI on HTTPS sites

A second change we’re introducing addresses what happens when a page served over a secure connection contains Mixed Content. Firefox’s Mixed Content Blocker proactively blocks Mixed Active Content by default. Users historically saw a shield icon when Mixed Active Content was blocked and were given the option to disable the protection.

Since the Mixed Content state is closely tied to site security, the information should be communicated in one place instead of having two separate icons. Moreover, we have seen that the number of times users override mixed content protection is slim, and hence the need for dedicated mixed content iconography is diminishing. Firefox is also using the shield icon for another feature in Private Browsing Mode and we want to avoid making the iconography ambiguous.

The updated design that ships with Firefox 42 combines the lock icon with a warning sign which represents Mixed Content. When Firefox blocks Mixed Active Content, we retain the green lock since the HTTP content is blocked and hence the site remains secure.

For users who want to learn more about a site’s security state, we have added an informational panel to further explain differences in page security. This panel appears anytime a user clicks on the lock icon in the address bar.

Previously users could click on the shield icon in the rare case they needed to override mixed content protection. With this new UI, users can still do this by clicking the arrow icon to expose more information about the site security, along with a disable protection button.

mixed active content click and subpanel

Users can click the lock with warning icon and proceed to disable Mixed Content Protection.

Loading Mixed Passive Content on HTTPS sites

There is a second category of Mixed Content called Mixed Passive Content. Firefox does not block Mixed Passive Content by default. However, when it is loaded on an HTTPS page, we let the user know with iconography and text. In previous versions of Firefox, we used a gray warning sign to reflect this case.

We have updated this iconography in Firefox 42 to a gray lock with a yellow warning sign. We degrade the lock from green to gray to emphasize that the site is no longer completely secure. In addition, we use a vibrant color for the warning icon to amplify that there is something wrong with the security state of the page.

We also use this iconography when the certificate or TLS connection used by the website relies on deprecated cryptographic algorithms.

The above changes will be rolled out in Firefox 42. Overall, the design improvements make it simpler for our users to understand whether or not their interactions with a site are secure.

Firefox Mobile

We have made similar changes to the site security indicators in Firefox for Android, which you can learn more about here.

Continuing to Phase Out SHA-1 Certificates

In our previous blog post about phasing out certificates with SHA-1 based signature algorithms, we said that we planned to take a few actions with regard to SHA-1 certificates:

  1. Add a security warning to the Web Console to remind developers that they should not be using a SHA-1 based certificates
  2. Show the “Untrusted Connection” error whenever a SHA-1 certificate issued after January 1, 2016, is encountered in Firefox
  3. Show the “Untrusted Connection” error whenever a SHA-1 certificate is encountered in Firefox after January 1, 2017

We have completed the first two of these steps.  We added the security warning to the Web Console in Firefox 38. If you open the Web Console and browse to a website with an SSL certificate that is SHA-1 based or is signed by a SHA-1 based intermediate certificate, you will get the following message in the console:

This site makes use of a SHA-1 Certificate; it’s recommended you use certificates with signature algorithms that use hash functions stronger than SHA-1. [Learn More]

In Firefox 43 we plan to show an overridable “Untrusted Connection” error whenever Firefox encounters a SHA-1 based certificate that has ValidFrom after Jan 1, 2016. This includes the web server certificate as well as any intermediate certificates that it chains up to. Root certificates are trusted by virtue of their inclusion in Firefox, so it does not matter how they are signed. However, it does matter what hash algorithm is used in the intermediate signatures, so the rules about phasing out SHA-1 certificates applies to both the web server certificate and the intermediate certificates that sign it.

We are re-evaluating when we should start rejecting all SHA-1 SSL certificates (regardless of when they were issued).  As we said before, the current plan is to make this change on January 1, 2017.  However, in light of recent attacks on SHA-1, we are also considering the feasibility of having a cut-off date as early as July 1, 2016.

We do not currently plan to display an error if an OCSP response is signed by a SHA-1 certificate. According to section 7.1.3 of version 1.3 of the CA/Browser Forum Baseline Requirements: “CAs MAY continue to sign certificates to verify OCSP responses using SHA1 until 1 January 2017.” Additionally, we do not currently plan to throw an error when SHA-1 S/MIME and client authentication certificates are encountered.

Questions about SHA-1 based certificates should be directed to the mozilla.dev.security.policy forum.

Deprecating the RC4 Cipher

As part of our commitment to protect the privacy of our users, Mozilla will disable the insecure RC4 cipher in Firefox in late January 2016, beginning with Firefox 44. Mozilla will be taking this action in coordination with the Chrome and IE/Edge teams. If you’re a web site operator and still rely on RC4, you need to enable some other ciphers, or Firefox users will be unable to reach you.  Very few servers rely exclusively on RC4, so most users should experience minimal disruption.

The Rise and Gradual Fall of RC4

Developed in 1987 by Ron Rivest, the RC4 cipher has been a staple of cryptography for almost 30 years.  For many years, RC4 was widely used by HTTPS servers: first because it was faster than contemporary alternatives, and later because it was immune to attacks that other ciphers were vulnerable to, such as BEAST.

Over the years, however, cryptanalysis of RC4 has resulted in better and better attacks against it.  It has been known since 1995 that RC4 has certain biases that make it easier to attack.  Recently, several practical attacks against RC4-protected HTTPS sessions have been demonstrated.  This led the IETF to publish RFC 7465, which forbids the use of RC4 in TLS.

At the same time, newer ciphers such as AES-GCM have been created, which are as fast as RC4 on modern hardware, and are also immune to attacks such as BEAST.  Most web servers support these newer ciphers, and the majority of Firefox TLS transactions already use them.

Deprecation of RC4 in Firefox

Until recently, RC4 was fully supported by Firefox to maintain compatibility with older servers, but over the past year, we’ve been gradually removing support.

In Firefox 36 (released in February 2015), we took the first step by making RC4 a “fallback-only” cipher.  With that change, Firefox would first try to communicate with the server using secure ciphers, before “falling back” to RC4.  As a result, Firefox would only use RC4 if the server didn’t support anything better.  That was a major step; over the course of the following weeks, RC4 usage by Firefox dropped from around 27% of TLS transactions to less than 0.5%.

In Firefox 38 (released in May 2015), we took a further step by disabling RC4 almost entirely in our pre-release Nightly and Developer Edition products, leaving it enabled only for a small whitelist of sites.  Web developers using those products to test their sites will have already seen breakage if their site requires RC4.  Perhaps as a result of this, RC4 usage by Firefox has continued to gradually decline, to the point where it’s currently used in only 0.08% of TLS transactions.

Disabling RC4 by Default

RC4 will no longer be offered by default in TLS fallback beginning with Firefox 44, set to be released on January 26, 2016. As a result, Firefox will refuse to negotiate RC4 with web servers. We are announcing this change now in order to provide website operators with time to update their websites.

As noted above, the share of Firefox TLS communications using RC4 has fallen from approximately 27% at the end of 2014 to only .08% at present.  As such, Mozilla expects the impact from this change to be minimal and localized to a small number of websites that currently only offer RC4 and are unable to upgrade prior to January.

Mozilla maintains a set of guidelines on TLS configurations and a TLS configuration generator to assist website operators in the selecting a secure configuration for their websites. Although it is recommended that website operators remove the availability of RC4 entirely, those that require compatibility with older clients such as Internet Explorer 6 may want to continue to offer RC4.  As long as more modern ciphers suites containing AES are also available, Firefox will use those more secure options instead of RC4.

Users that would like to disable RC4 fallback prior to the January release may set the security.tls.unrestricted_rc4_fallback setting inside of about:config to false.  After that preference is set to false by default in Firefox 44, users that still require RC4 may re-enable it by setting it back to true.

Improving Security for Bugzilla

The Bugzilla bug tracker is a major part of how we accomplish our mission of openness at Mozilla. It’s a tool for coordinating among our many contributors, and a focal point for community interactions. While most information in Bugzilla is public, Bugzilla restricts access to security-sensitive information, so that only certain privileged users can access it.

It is in the same spirit of openness that we are disclosing today that someone was able to steal security-sensitive information from Bugzilla.  We believe they used that information to attack Firefox users. Mozilla has conducted an investigation of this unauthorized access, and we have taken several actions to address the immediate threat.  We are also making improvements to Bugzilla to ensure the security of our products, our developer community, and our users.

The account that the attacker broke into was shut down shortly after Mozilla discovered that it had been compromised.  We believe that the attacker used information from Bugzilla to exploit the vulnerability we patched on August 6.  We have no indication that any other information obtained by the attacker has been used against Firefox users.  The version of Firefox released on August 27 fixed all of the vulnerabilities that the attacker learned about and could have used to harm Firefox users.

We are updating Bugzilla’s security practices to reduce the risk of future attacks of this type. As an immediate first step, all users with access to security-sensitive information have been required to change their passwords and use two-factor authentication. We are reducing the number of users with privileged access and limiting what each privileged user can do. In other words, we are making it harder for an attacker to break in, providing fewer opportunities to break in, and reducing the amount of information an attacker can get by breaking in.

Openness, transparency, and security are all central to the Mozilla mission. That’s why we publish security bugs once they’re no longer dangerous, and it’s why we’re writing a blog post about unauthorized access to our infrastructure. We have notified the relevant law enforcement authorities about this incident, and may take additional steps based on the results of any further investigations.

For more details, please see our FAQ document.