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Surveys by security researchers has revealed that around 300,000 servers and more than 30,000 websites are still vulnerable to the Heartbleed bug that affects certain versions of OpenSSL.

Security researcher Robert Graham had scanned the Internet (port 443) last month and found some 600,000 vulnerable servers. He decided to rescan this month in order to gauge mitigation efforts, and found that 318,239 servers were still vulnerable to the Heartbleed flaw.

“This was a scan of IPv4 addresses. Scans starting from DNS domain-names produce wildly different results. A lot of news stories focus on things like “the top million domain names”, the results of which are unrelated to this scan,” Graham noted. “This scan was only port 443. I really should scan for other well-known SSL ports, like SMTP ports. If I get around to that, I’ll post the results.”

Graham also found that 1.5-million systems were still supporting the vulnerable “heartbeat” feature, with most patched save for the 300k he detected in this scan.

“This implies to me that the first response to the bug was to disable heartbeats, then later when people correctly patched the software, heartbeats were re-enabled,” Graham explained. “Note that only OpenSSL supports heartbeats, meaning that the vast majority of SSL-supporting servers are based on software other than OpenSSL.”

Another survey conducted by Netcraft found that well over 30,000 TLS/SSL certificates have been revoked in response to Heartbleed and then subsequently had been reissued with the same keys, leaving them still vulnerable.

“Although many secure websites reacted promptly to the Heartbleed bug by patching OpenSSL, replacing their SSL certificates, and revoking the old certificates, some have made the critical mistake of reusing the potentially-compromised private key in the new certificate.” wrote Netcraft’s Paul Mutton. “Since the Heartbleed bug was announced on 7 April, more than 30,000 affected certificates have been revoked and reissued without changing the private key.”

Mutton explains that in reusing the same private key, websites vulnerable to Heartbleed face the same risk of exploitation as sites that have not replaced their SSL certificates at all.

“If the previous certificate had been compromised, then the stolen private key can still be used to impersonate the website’s new SSL certificate, even if the old certificate has been revoked,” Mutton continued. “Certificates that have been reissued with the same private key are easy to identify, as the new public key will also be identical to the old one.”

Mutton suggests that these kinds of mistakes could be prevented of certificate authorities (CA’s) blacklisted the public keys from revoked certificates.

“This type of automated check does not seem to be in use by most CAs; however, Netcraft’s Site Reports and browser extensions can be used to determine whether a website has signed its replacement certificate with the same private key,” Graham said.