CVE-2021-47010: Linux Kernel

High severity, CVSS 7.8. EPSS: 0.3% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: net: Only allow init netns to set default tcp cong to a restricted algo tcp_set_default_congestion_control() is netns-safe in that it writes to &net->ipv4.tcp_congestion_control, but it also sets ca->flags |= TCP_CONG_NON_RESTRICTED which is not namespaced. This has the unintended side-effect of changing the global net.ipv4.tcp_allowed_congestion_control sysctl, despite the fact that it is read-only: 97684f0970f6 ("net: Make tcp_allowed_congestion_control readonly in non-init netns") Resolve this netns "leak" by only allowing the init netns to set the default algorithm to one that is restricted. This restriction could be removed if tcp_allowed_congestion_control were namespace-ified in the future. This bug was uncovered with https://github.com/JonathonReinhart/linux-netns-sysctl-verify

Affected products

• Linux Linux Kernel: from 4.15, before 4.19.191 (fixed in 4.19.191); from 4.20, before 5.4.119 (fixed in 5.4.119); from 5.5, before 5.10.37 (fixed in 5.10.37); from 5.11, before 5.11.21 (fixed in 5.11.21); from 5.12, before 5.12.4 (fixed in 5.12.4)

Published 2024-02-28. Last modified 2026-06-17.