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Fencer Vulns
high 7.8

CVE-2021-47010 json

net: Only allow init netns to set default tcp cong to a restricted algo

published 2024-02-28 2 y ago modified 2026-06-17 4 mo ago also EUVD-2021-33658

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits
0
none known

Summary

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

Patch / fix

  • Linux Linux 4.19.191, 5.4.119, 5.10.37, 5.11.21, 5.12.4, 5.13
  • linux linux_kernel 4.19.191, 5.4.119, 5.10.37, 5.11.21, 5.12.4, 5.13, 6c1ea8bee75d, 8d432592f30f, 992de06308d9, 9884f745108f, e7d7bedd507b, efe1532a6e1a
  • linux Debian 14, Debian 13, Debian 12 5.10.38-1

debian advisories DEBIAN-CVE-2021-47010

  • linux Ubuntu 18.04 LTS 4.15.0-151.157
  • linux Ubuntu 20.04 LTS 5.4.0-77.86
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1109.116
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1051.53
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1046.49
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1097.99
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1041.42
  • linux-azure Ubuntu 20.04 LTS 5.4.0-1051.53

ubuntu advisories UBUNTU-CVE-2021-47010

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-47010 updated cvss 4.4

kernel: net: Only allow init netns to set default tcp cong to a restricted algo

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix available
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2 y ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux
  • linux linux_kernel

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.