Karthikeyan Bhargavan and Gaetan Leurent at INRIA discovered a flaw in the TLS 1.2 protocol which could allow the MD5 hash function to be used for signing ServerKeyExchange and Client Authentication packets during a TLS handshake. A man-in-the-middle attacker could exploit this flaw to conduct collision attacks to impersonate a TLS server or an authenticated TLS client.
More information can be found at <https://www.mitls.org/pages/attacks/SLOTH>
For the oldstable distribution (wheezy), this problem has been fixed in version 1.0.1e-2+deb7u19.
For the stable distribution (jessie), the testing distribution (stretch) and the unstable distribution (sid), this issue was already addressed in version 1.0.1f-1.
We recommend that you upgrade your openssl packages.