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

CVE-2024-42256CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: cifs: Fix server re-repick on subrequest retry When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server. If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting. Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry. The problem manifests as a warning looking something like: WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.
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.
CVE-2024-38612CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: sr: fix invalid unregister error path The error path of seg6_init() is wrong in case CONFIG_IPV6_SEG6_LWTUNNEL is not defined. In that case if seg6_hmac_init() fails, the genl_unregister_family() isn't called. This issue exist since commit 46738b1317e1 ("ipv6: sr: add option to control lwtunnel support"), and commit 5559cea2d5aa ("ipv6: sr: fix possible use-after-free and null-ptr-deref") replaced unregister_pernet_subsys() with genl_unregister_family() in this error path.
CVE-2024-38623CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: fs/ntfs3: Use variable length array instead of fixed size Should fix smatch warning: ntfs_set_label() error: __builtin_memcpy() 'uni->name' too small (20 vs 256)
CVE-2021-47548CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ethernet: hisilicon: hns: hns_dsaf_misc: fix a possible array overflow in hns_dsaf_ge_srst_by_port() The if statement: if (port >= DSAF_GE_NUM) return; limits the value of port less than DSAF_GE_NUM (i.e., 8). However, if the value of port is 6 or 7, an array overflow could occur: port_rst_off = dsaf_dev->mac_cb[port]->port_rst_off; because the length of dsaf_dev->mac_cb is DSAF_MAX_PORT_NUM (i.e., 6). To fix this possible array overflow, we first check port and if it is greater than or equal to DSAF_MAX_PORT_NUM, the function returns.

References

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