On November 26, Canonical published details about libssh vulnerabilities for its Ubuntu 12.10, Ubuntu 12.04 LTS, Ubuntu 11.10, and Ubuntu 10.04 LTS operating systems.
According to Canonical, libssh could have been made to crash or run programs if it received specially crafted network traffic.
It discovered that libssh incorrectly handled the memory. A remote attacker could have used this problem to cause libssh to crash, resulting in a denial of service, or possibly execute arbitrary code.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can simply fix the security flaws by upgrading the operating systems to the latest libssh-4 package, specific to each distribution.
A normal system update, executed with the Update Manager, will implement all the necessary changes. A complete system restart is not necessary.