Phishing Alerts for Certificate Authorities

The internet community has been taught that one of the key steps in protecting their personal information on the internet is to ensure that it is entered only over an encrypted connection, perhaps by looking for the lock symbol in the browser address bar or web addresses beginning with https://. As a result, phishing attacks which make use of SSL certificates are especially dangerous as most users associate the presence of a valid SSL certificate with an increased level of assurance. Such attacks erode the reputation of Certificate Authorities and SSL certificates.

While the majority of phishing attacks run over HTTP, a significant number run on sites for which SSL certificates have been issued. In July 2012 alone, Netcraft found phishing attacks using a total of 505 unique valid SSL certificates from widely trusted issuers.

Although in some cases certificates have been issued specifically for the purposes of phishing the more common case is where well intentioned, bona fide certificate owners find that they are unwittingly providing facilities for phishing because their site has been compromised by an attacker.

Having access to timely, professionally validated alerts when phishing attacks occur is operationally efficient and responsible for certificate authorities, as well as an important part of preserving their company's reputation. It gives post issuance information on troublesome certificates and domains of which the certificate authority might otherwise be blissfully unaware.

Phishing Alerts are also a very valuable service for certificate holders, for whom it may be the first notification of a serious problem, giving them an opportunity to engage the attacker and wrest back control of their site before more harm is done.

Netcraft produces a continuously updated phishing feed that is very widely used. At least three separate third party studies have found it to be the most comprehensive feed available. The feed is used in all the major web browsers and it is also licensed by many of the leading anti-virus, content filtering, web-hosting and domain registration companies.

Phishing sites are submitted to the feed by the Netcraft Toolbar community. Reporters range from individuals submitting phishing mails that they have personally received, to specialist security researchers and several of the largest banks and financial payment systems. All submissions are carefully validated before being added to the feed. Well over five million unique phishing sites have been detected and blocked by Netcraft's community to date [September 2012].

GlobalSign commenced providing this service to all of its certificate owners in August 2012 (press release), and in the first month of the service around 70 distinct certificate owners were alerted to phishing attacks on sites where their certificates were deployed.

More information:

Please contact us ( for pricing or further details about any of our services.

September 2012 Web Server Survey

In the September 2012 survey we received responses from 620,132,319 sites, a decrease of 8M sites since last month's survey.

A large portion of this drop was caused by a large network of linkfarmed domains disappearing from under the .com TLD, causing Apache numbers to suffer the most, with a loss of 10M sites. This resulted in a small drop in Apache's market share to 58%. Google also saw losses of 1M sites, but both Microsoft and nginx gained, with 840k and 1.5M new domains respectively.

Server headers for IIS 8.0 – the latest version of Microsoft's server software – were returned by 1,723 sites this month. This is an increase of 1,445 sites (+519%) over the six months since the public beta release of Windows Server 2012 in April, which uses IIS 8.0 as its default web server. However, only twelve of the million busiest sites were found to be using the software, seven of which are within Microsoft's own

Amazon reached a significant milestone this month, with its strong and continued growth in the web hosting market now making it the world's largest hosting location by number of web-facing computers. The previous leader was China Telecom, which now has 116k web-facing computers against Amazon's 118k.

Netcraft's hosting provider server count uses a set of heuristics to identify individual computers, regardless of how many web-facing IP addresses each may have, or how many websites they serve.

Amazon has nearly doubled its count of web-facing computers within the past year, and this growth does not look set to slow down any time soon. The majority of these computers are located in the US (77%) and Ireland (13%), although smaller numbers of servers have started popping up in other locations within the past year, including the Netherlands, Singapore, Brazil, and Japan.

Although Amazon has the largest number of web-facing computers, these are used to host a relatively modest sum of 6.8M websites. 2.9M of these sites are served by nginx, which is closely followed by 2.3M served by Apache. A further 410k are served by Polyvore Web Server, which is used by sites within the Polyvore fashion social-commerce network. Only 2.4% (163k) of the sites hosted at Amazon are running Microsoft IIS.

Although Amazon's scalable, pay-as-you-go EC2 service supports Microsoft Windows, Linux is by far the most popular operating system to be found amongst all of its web-facing computers, including those used by CloudFront and S3. Nearly 97% of Amazon's web-facing computers were running Linux during September's survey.

DeveloperAugust 2012PercentSeptember 2012PercentChange
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Minimum RSA public key lengths: guidelines or rules?

The length of an RSA public key gives an indication of the strength of the encryption — the shorter the public key is; the easier it is for an attacker to brute-force. An attacker, armed with a compromised private key derived from a short public key, would be able to decrypt both past and future SSL-secured connections if she were able to incept the encrypted traffic. She could also impersonate the organisation to which the SSL certificate was issued if she has the opportunity to manipulate DNS lookups. Both the CA/B Forum (a consortium of certificate authorities (CAs) and major browser vendors) and NIST [PDF] (the agency which publishes technical standards for US governmental departments) have recommended that sub-2048-bit RSA public keys be phased out by the end of 2013.

According to the CA/B Forum's own Baseline Requirements [PDF] — effective 1st July 2012 — member certificate authorities are required to reject a request to sign an RSA public key shorter than specified in the following table:

Certificate expiry date Minimum RSA public key length
On or before 31st December 2013 1024
After 31st December 2013 2048

Nevertheless, these key sizes are not guaranteed as several CA/B Forum members have issued several non-compliant SSL certificates since 1st July 2012. Trustwave, Symantec, KEYNECTIS, and TAIWAN-CA have all signed certificates which fall foul of their organisation's requirement of 2048-bit RSA public keys for certificates expiring after 2013, demonstrating that the key length requirement is being treated as a guideline (which by definition is neither binding nor enforced), rather than a rule.

They are by no means the only CAs signing short RSA public keys: more than 10 years after Netcraft's first blog post on the topic and 12 years after RSA-155 [PDF], 512-bit RSA public keys are still appearing in SSL certificates. A 512-bit RSA public key was signed as recently as July 2012 by Swisscom.

Most, but not all, of the major browser and operating system vendors either disallow access or display a warning message when accessing a website using an SSL certificate with a 512-bit RSA public key. The latest versions of Safari (although not the mobile version on iOS 5.1), Opera, Google Chrome, and Internet Explorer (via an update to Windows; planned to be rolled out in October 2012). Notably, Mozilla Firefox does not yet reject such certificates.

Most Reliable Hosting Company Sites in August 2012

Rank Company site OS Outage
DNS Connect First
1 Qube Managed Services Linux 0:00:00 0.003 0.170 0.133 0.270 0.271
2 Datapipe FreeBSD 0:00:00 0.007 0.079 0.017 0.036 0.054
3 iWeb Technologies Linux 0:00:00 0.007 0.127 0.085 0.170 0.170
4 Windows Server 2008 0:00:00 0.007 0.045 0.139 0.281 0.701
5 XILO Communications Ltd. Linux 0:00:00 0.007 0.376 0.141 0.406 0.687
6 Linux 0:00:00 0.010 0.172 0.073 0.180 0.219
7 New York Internet FreeBSD 0:00:00 0.013 0.150 0.071 0.223 0.500
8 INetU Windows Server 2008 0:00:00 0.013 0.105 0.093 0.271 0.549
9 Server Intellect Windows Server 2008 0:00:00 0.017 0.149 0.055 0.111 0.278
10 Linux 0:00:00 0.020 0.213 0.089 0.183 0.261

See full table

Qube Managed Services, a London-based company which specialises in virtual hosting, was the most reliable hosting company in August. With infrastructure in London, Zurich and New York, they provide Virtual Data Centres and Managed Hosting in addition to server co-location. Having placed in the top 10 twice before in the past six months, Qube's top place this month is well-deserved with 99.997% of requests succeeding.

Datapipe and iWeb Technologies placed second and third this month with the same percentage of successful requests. Datapipe, whose connection times were on average faster, runs its data centres entirely on renewable energy and are recognised by the Environmental Protection Agency as a Green Power partner. iWeb offers dedicated and virtual servers in addition to a number of advanced solutions such as Web Clusters, ideal for customers requiring high availability.

Netcetera and XILO also both placed highly this month with the same number of successful requests as Datapipe and iWeb, putting them in fourth and fifth places respectively.

As we've seen in previous months, the most reliable hosting companies are all powered by Linux, FreeBSD or Windows Server 2008. The last time a different operating system placed in the top 10 was when Windows Server 2003 appeared, back in February.

Netcraft measures and makes available the response times of around forty leading hosting providers' sites. The performance measurements are made at fifteen minute intervals from separate points around the internet, and averages are calculated over the immediately preceding 24 hour period.

From a customer's point of view, the percentage of failed requests is more pertinent than outages on hosting companies' own sites, as this gives a pointer to reliability of routing, and this is why we choose to rank our table by fewest failed requests, rather than shortest periods of outage. In the event the number of failed requests are equal then sites are ranked by average connection times.

Information on the measurement process and current measurements is available.

Governments and banks still using weak MD5-signed SSL certificates

More than a thousand websites – including several government sites – are still using SSL certificates with weak signature algorithms.

Netcraft's August 2012 SSL Survey shows there are 1,300 websites still using SSL certificates that have been signed using the cryptographically weak MD5 digest algorithm. This algorithm is demonstrably vulnerable to several types of attack, including collision attacks.

The first use of this vulnerability against SSL was demonstrated back in December 2008, when security researchers showed how an MD5 hash collision could be exploited to create a rogue certificate authority (CA) certificate that would be trusted by all common web browsers. This rogue certificate could have been used to sign arbitrary subscriber certificates, thus allowing an attacker to convincingly impersonate any secure website on the internet.

At the time of the 2008 discovery, Netcraft's SSL Survey showed that 14% of all SSL certificates were signed using the vulnerable MD5 algorithm.

A few months later, the developers of Google Chrome suggested that some browser developers would be dropping support for MD5-signed certificates at some point; however, given the number of sites still using MD5-signed certificates, it was thought that suddenly removing support for such certificates would have a undesirably large impact on users.

As the majority of MD5-signed certificates have since expired or been replaced, browser vendors and certificate authorities have been gradually phasing out support for such certificates. Apple removed support for MD5-signed certificates in an iOS 5 update last year, and Chrome's developers subsequently revisited the issue and revised their browser to display an interstitial warning about MD5 being a weak signature algorithm. This immediately caused problems for users of certain corporate proxies, where a man-in-the-middle approach was used to decrypt SSL traffic before presenting it to the client with a trusted MD5-signed certificate.

The CA GeoTrust has added the affected certificates to its certificate revocation lists at, which has resulted in the certificates being rejected as invalid in many of today's browsers, including Chrome, Opera and Internet Explorer. However, sites which currently use MD5-signed certificates can be viewed with the latest version of Mozilla Firefox without receiving any warnings, as the relevant certificate revocation lists have to be added manually, and none of the certificates specifies an OCSP server for checking the revocation status.

The CA/Browser Forum Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates [pdf] no longer allow the MD5 digest algorithm to be used for root, subordinate or subscriber certificates. All but two of the 1,123 unique MD5-signed certificates still in use on the web were issued by Equifax between 2006 and 2008, with validity periods ranging between 4 and 6 years.

The remaining two MD5-signed certificates were issued by VeriSign. These do not appear to have been revoked, but are due to expire in less than a month. In the worst case, all MD5-signed certificates currently in use on the web will have expired naturally by March 2014, regardless of whatever measures have been taken by browser vendors and certificate authorities.

Several government websites are currently operating with MD5-signed certificates, including a few in Australia, a couple in New Zealand, and one in each of Ireland and the UK. The most recently issued certificates are marked as being valid from 30th December 2008 – the same day as the publication of the hash collision demonstration.

Other notable users of weak MD5-signed certificates include Reliance Bank, Commencement Bank, several online billing websites, dozens of corporate webmail services, purportedly secure hosting providers, a number of schools and universities, and even a reseller of GeoTrust SSL certificates.

Phishing on sites using SSL Certificates

Over the years the Internet community has been taught that one of the key steps in protecting their personal information on the Internet is to ensure that it is entered only over an encrypted connection, perhaps by looking for the lock symbol in the browser address bar or web addresses beginning with https://. As a result, phishing attacks which make use of SSL certificates are especially dangerous  as most users associate the presence of a valid SSL certificate with an increased level of assurance. Such attacks  erode the reputation of Certificate Authorities and SSL certificates, which makes identifying and revoking maliciously used certificates a material issue.

Netcraft's anti-phishing feed has blocked over 5 million unique phishing sites to date, receiving over 4 reports a minute from our reporter community, and while the majority of phishing attacks run over HTTP,  a significant number run on sites for which SSL certificates have been issued. In July 2012 alone, Netcraft found 505 unique valid certificates on blocked sites.

The following table, produced for the Netcraft SSL Survey, shows the number of unique valid certificates returned by phishing sites that were blocked by Netcraft in July 2012:

Certificate Authority (CA) Unique certificates ...with matching Common Names ...and accessed by https://
Symantec 216 41 21
Comodo 130 16 7
Go Daddy 67 19 8
Other 41 11 6
GlobalSign 39 2 1
DigiCert 12 2 2

The columns of the table are ordered left to right by trustworthiness, as using a valid SSL certificate is not always enough to trick a user into trusting a phishing website and two further conditions have to be met:

  • The Subject Common Name of the certificate has to match the hostname of the phishing site that returned it. Some sites will return the hosting company's certificate when requested over HTTPS. As most modern browsers display warnings when a non-matching certificate is encountered (pictured below), such certificates only serve to make the user more suspicious instead of increasing the perceived security of the site.
  • A phishing site accessed over HTTPS displays the SSL certificate for the hosting company.
  • The phishing attack has to actively use the SSL certificate by including https:// in the phishing URL. Having a valid SSL certificate does not make a phishing site appear more trustworthy if victims only access it over HTTP.

Fraudsters will often host their phishing content on a compromised website and so can make use of the website's legitimate certificate, however they may not have realized that SSL services are available and so serve the content over HTTP. None of the certificates found on phishing sites in this period appeared to have been issued specifically for the purpose of phishing.

Taking Certificate Authority market shares into consideration, Go Daddy has a lower proportion of its SSL certificates used in phishing attacks than the other large CAs, in part because it provides the hosting for a large proportion of the certificates which they issue and is a long term user of Netcraft's feed to remove phishing attacks.