Issues have been identified in the way the Linux kernel’s TCP implementation processes Selective Acknowledgement (SACK) options and handles low Maximum Segment Size (MSS) values. These TCP SACK Panic vulnerabilities could expose servers to a denial of service attack, so it is crucial to have systems patched.
Updated versions of the Linux kernel packages are being published as part of the standard Ubuntu security maintenance of Ubuntu releases 16.04 LTS, 18.04 LTS, 18.10, 19.04 and as part of the extended security maintenance for Ubuntu 14.04 ESM users.
Livepatch fixes for CVEs 2019-11477 and 2019-11478 are not available for prior kernels, and an upgrade and reboot to the appropriate minimum version is necessary. These kernel versions correspond to the availability of mitigations for the MDS series of CVEs (CVE-2018-12126, CVE-2018-12127, CVE-2018-12130 and CVE-2019-11091).
Additionally, a third SACK related issue, CVE-2019-11479, does not have a Livepatch fix available because it is not technically feasible to apply the changes via Livepatch. Mitigation information is available at the Ubuntu Security Team Wiki.
If you have any questions and want to learn more about these patches, please do not hesitate to get in touch.