high CVSS 7.8

CVE-2021-47010·Kernel vulnerability

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

Severity
high
Software
Kernel
Fixed in
5.12.4
Published
2024-02-28

Affected versions

From: 5.12

Until: 5.12.4

Fixed in: 5.12.4

How to fix this CVE

Update your Linux kernel to version 5.12.4 or later to patch this network namespace isolation vulnerability. The vulnerability allows unprivileged users in non-init namespaces to inadvertently modify global TCP congestion control settings, potentially affecting system-wide networking behavior. Ensure your kernel is fully patched to restore proper namespace isolation boundaries.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check kernel version with `uname -r` and compare against 5.12.4 or later; versions 5.12.0 through 5.12.3 are vulnerable
  2. Step 2: Verify if untrusted users have network namespace creation privileges with `grep -r 'user_namespaces' /boot/config-$(uname -r)` and check if CONFIG_USER_NS is enabled
  3. Step 3: Monitor /var/log/auth.log (Ubuntu/Debian) or /var/log/audit/audit.log (RHEL/CentOS) for repeated failed or successful attempts to modify /proc/sys/net/ipv4/tcp_congestion_control from non-init namespaces
  4. Step 4: After patching, verify the fix with `uname -r` returns 5.12.4 or higher, and confirm net namespace restrictions are enforced by testing namespace creation permissions remain limited

FAQ

What is CVE-2021-47010?

CVE-2021-47010 is a Linux kernel vulnerability where unprivileged users in non-init network namespaces can modify global TCP congestion control algorithm flags, bypassing namespace isolation and potentially affecting the entire system's networking configuration despite read-only sysctl protections.

Is CVE-2021-47010 being actively exploited?

No, CVE-2021-47010 is not listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploits are currently available.

What versions of Kernel are affected by CVE-2021-47010?

Linux kernel versions 5.12 through 5.12.3 are affected; version 5.12.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2021-47010?

Run `uname -r` to display your kernel version; if it reports 5.12.0 through 5.12.3, your system is vulnerable and should be patched immediately.

Does Defensia detect CVE-2021-47010?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47010 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2024-39462CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: clk: bcm: dvp: Assign ->num before accessing ->hws Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by") annotated the hws member of 'struct clk_hw_onecell_data' with __counted_by, which informs the bounds sanitizer about the number of elements in hws, so that it can warn when hws is accessed out of bounds. As noted in that change, the __counted_by member must be initialized with the number of elements before the first array access happens, otherwise there will be a warning from each access prior to the initialization because the number of elements is zero. This occurs in clk_dvp_probe() due to ->num being assigned after ->hws has been accessed: UBSAN: array-index-out-of-bounds in drivers/clk/bcm/clk-bcm2711-dvp.c:59:2 index 0 is out of range for type 'struct clk_hw *[] __counted_by(num)' (aka 'struct clk_hw *[]') Move the ->num initialization to before the first access of ->hws, which clears up the warning.
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CVE-2024-36031CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: keys: Fix overwrite of key expiration on instantiation The expiry time of a key is unconditionally overwritten during instantiation, defaulting to turn it permanent. This causes a problem for DNS resolution as the expiration set by user-space is overwritten to TIME64_MAX, disabling further DNS updates. Fix this by restoring the condition that key_set_expiry is only called when the pre-parser sets a specific expiry.

References

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