Server administrators are advised to upgrade OpenSSL again to fix eight new vulnerabilities, two of which can lead to denial-of-service (DoS) attacks.

The flaws are only of moderate and low severity, unlike the Heartbleed vulnerability discovered last year. Heartbleed could have allowed attackers to steal sensitive information including encryption keys from servers.

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Nevertheless, "system administrators should plan to upgrade their running OpenSSL server instances in the coming days," said Tod Beardsley, engineering manager at vulnerability intelligence firm Rapid7, via email Friday.

The newly released OpenSSL versions are 1.0.1k, 1.0.0p and 0.9.8zd.

Two denial-of-service vulnerabilities, tracked as CVE-2014-3571 and CVE-2015-0206, only affect OpenSSL's implementation of the DTLS (Datagram Transport Layer Security) protocol, which is not as widely used as the TLS (Transport Layer Security) protocol.

DTLS provides encrypted communications over datagram protocols such as UDP and is used for things like VPN (Virtual Private Networks) and WebRTC (Web Real-Time Communication).

"In order to maintain reliable service, OpenSSL should be upgraded or replaced by SSL libraries not affected by these issues, such as LibreSSL," Beardsley said.

Other flaws do apply to TLS and can lead to unexpected behavior when OpenSSL is built with the no-ssl3 option, a situation where the server accepts DH certificates for client authentication without the certificate verify message and a case where a client accepts an ECDH handshake despite a missing server key exchange message, which removes the forward secrecy property of the ciphersuite.

"We are still looking into the issues disclosed today," Beardsley said. "While these vulnerabilities do not appear to lead to remote code execution or information disclosure, we will let the OpenSSL team know if we find any new, unexpected vectors of attack."