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Security at Yahoo remains poor despite commitments made when the company recently confirmed a 2014 data breach that affected half a billion users, according to security firm Venafi.
On 22 September, the internet firm said a “recent investigation” had revealed that the compromised data may have included names, email addresses, telephone numbers, dates of birth, hashed passwords, and some encrypted or unencrypted security questions and answers.
“Through strategic proactive detection initiatives and active response to unauthorised access of accounts, Yahoo will continue to strive to stay ahead of these ever-evolving online threats and to keep our users and our platforms secure,” Bob Lord, chief information security officer at Yahoo, said in a blog post.
But, according to Venafi Labs, Yahoo has not taken the necessary action to ensure users are not still exposed and that the hackers do not still have access to their systems and encrypted communications.
The researchers found Yahoo was still using MD5 cryptographic hashing function for many of its digital certificates, noting that this algorithm had been known to be vulnerable for several years and suffered from many serious and well-documented vulnerabilities.
Venafi analysed data from TrustNet, a global database of certificate intelligence, and found that 27% of the certificates on external Yahoo websites had not been reissued since January 2015.
According to the researchers, replacing certificates after a breach is a critical mitigation practice because if certificates are not replaced, breached organisations cannot be certain that attackers do not have continuing access to encrypted communications.
Only 2.5% of the 519 certificates deployed have been issued within the last 90 days. According to Venafi, it is likely Yahoo does not have the ability to find and replace digital certificates quickly, which is a common problem, even in very large organisations with a significant online presence.
Venafi researchers found that all the MD5 certificates in use by Yahoo today and many of the other certificates Venafi evaluated were self-issued, and one current MD5 certificate used wildcard certificate (*.yahoo.com) and had an expiration date of five years.
According to the researchers, certificates with long expirations dates, those that are self-issued and those that use wild cards are all symptoms of weak cryptographic control.
They also found that 41% of the external Yahoo certificates in the TrustNet data set used SHA-1, a hashing algorithm that was no longer considered secure against well-funded opponents. The major browser suppliers have said they will stop accepting SHA-1 certificates in January 2017.
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Alex Kaplunov, vice-president of engineering for Venafi, said major breaches such as the one suffered by Yahoo were often accompanied by relatively weak cryptographic controls.
“To confirm this assumption, we took an in-depth look at externally facing Yahoo web properties and the details of how these sites are using cryptography,” he said. “We found the encryption practices on these properties to be relatively weak. This is not surprising. In our experience, most enterprises, even global brands with deep cyber security investments, have weak cryptographic controls.”
Hari Nair, director of product management and cryptographic researcher for Venafi, said any one of the cryptographic issues identified at Yahoo would leave any organisation extremely vulnerable to attacks on encrypted communication and authentication.
“Collectively, they pose serious questions about whether Yahoo has the visibility and technology necessary to protect encrypted communications and ensure its customers privacy,” he said. “Our research has led us to believe that there is usually a high degree of co-relation between weak cryptographic controls and overall cyber security posture.”
Kevin Bocek, chief security strategist at Venafi, said the fact that the attackers had been able to exfiltrate data on 500 million Yahoo users meant they were likely to have used encryption against Yahoo to ensure their activities were undetected by the firm’s security controls.
“It is nearly impossible for any organisation to detect unauthorised, encrypted traffic coming in or out unless they have strong cryptography practices,” he said.
Bocek emphasised that encrypting data was not enough to ensure security and privacy. “A range of technical encryption properties must be combined to ensure security and privacy, which is one reason that, in spite of enormous investments in cyber security technology by every type of organisation, we continue to see a constant stream of major breaches,” he said.
Commenting on the fact that Yahoo has not replaced cryptographic keys and digital certificates over the past 90 days, Bocek said there did not appear to be a co-ordinated response to a breach.
“Known vulnerabilities like MD5 certificates combined with a wildcard certificate that has a five-year expiration date makes it clear that Yahoo lacks deep visibility into its cryptographic security posture,” he said.
Bocek warned that organisations that used encryption to secure everything – without a comprehensive understanding of cryptographic risks – could not be confident about security or privacy.