Positive Technologies Discovers and Patches Linux Kernel Vulnerabilities

Positive Technologies security researcher Alexander Popov has discovered and fixed five similar issues in the virtual socket implementation of the Linux kernel. These vulnerabilities could be exploited for local privilege escalation, as confirmed by Popov in experiments on Fedora 33 Server. The vulnerabilities, known together as CVE-2021-26708, have received a CVSS v3 base score of 7.0 (high severity).

These vulnerabilities result from race conditions[1] that were implicitly added with virtual socket multi-transport support. They appeared in Linux kernel version 5.5 in November 2019. The vulnerable kernel drivers (CONFIG_VSOCKETS and CONFIG_VIRTIO_VSOCKETS) are shipped as kernel modules in all major GNU/Linux distributions. The vulnerable modules are automatically loaded when an AF_VSOCK socket is created. This ability is available to unprivileged users.

Popov said: “I successfully developed a prototype exploit for local privilege escalation on Fedora 33 Server, bypassing x86_64 platform protections such as SMEP and SMAP. This research will lead to new ideas on how to improve Linux kernel security.”

Popov prepared the fixing patch and disclosed the vulnerabilities responsibly to the Linux kernel security team. The patch has been merged into mainline kernel version 5.11-rc7 and backported into affected stable trees.

Previously, Popov discovered and fixed Linux kernel vulnerabilities CVE-2019-18683 and CVE-2017-2636.

About Positive Technologies


For 18 years, Positive Technologies has been creating innovative solutions for information security. We develop products and services to detect, verify, and neutralize the real-world business risks associated with corporate IT infrastructure. Our technologies are backed by years of research experience and the expertise of world-class cybersecurity experts. Over 2,000 companies in 30 countries trust us to keep them safe. Follow us on social media (LinkedIn, Twitter) and the News section at ptsecurity.com.


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