ELA-88-1 openssl security update

padding oracle attack

Related CVE CVE-2019-1559

Juraj Somorovsky, Robert Merget and Nimrod Aviram discovered a padding oracle attack in OpenSSL. If an application encounters a fatal protocol error and then calls SSL_shutdown() twice (once to send a close_notify, and once to receive one) then OpenSSL can respond differently to the calling application if a 0 byte record is received with invalid padding compared to if a 0 byte record is received with an invalid MAC. If the application then behaves differently based on that in a way that is detectable to the remote peer, then this amounts to a padding oracle that could be used to decrypt data.

In order for this to be exploitable “non-stitched” ciphersuites must be in use. Stitched ciphersuites are optimised implementations of certain commonly used ciphersuites. Also the application must call SSL_shutdown() twice even if a protocol error has occurred (applications should not do this but some do anyway). AEAD ciphersuites are not impacted.

For Debian 7 Wheezy, these problems have been fixed in version 1.0.1t-1+deb7u8.

We recommend that you upgrade your openssl packages.

Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/