high CVSS 7.1

CVE-2021-46952·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused by a garbage timeout (retrans) mount option being passed to nfs mount, in this case from syzkaller. If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift value for a 64-bit long integer, so 'retrans' cannot be >= 64. If it is >= 64, fail the mount and return an error.

Severity
high
Software
Kernel
Fixed in
5.12.3
Published
2024-02-27

Affected versions

From: 5.12.0

Until: 5.12.3

Fixed in: 5.12.3

How to fix this CVE

Update your Linux kernel to version 5.12.3 or later to patch this shift out-of-bounds vulnerability in NFS UDP transport handling. The vulnerability allows invalid retrans mount parameters to trigger a kernel crash. Ensure you test the kernel update in a non-production environment before rolling out to critical systems.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version: uname -r — verify it is 5.12.0, 5.12.1, or 5.12.2 (vulnerable range)
  2. Verify NFS UDP transport is enabled: grep -i 'proto=udp' /proc/mounts — if present, your system may be at higher risk
  3. Search kernel logs for shift-related panics: grep -i 'shift' /var/log/kern.log or journalctl -k | grep -i 'shift'
  4. Confirm patch applied: uname -r should show 5.12.3 or later; verify with: cat /boot/config-$(uname -r) | grep CONFIG_NFS

FAQ

What is CVE-2021-46952?

This vulnerability exists in the Linux kernel's NFS mount option validation for UDP transport. When an attacker or misconfigured system passes an extremely large retrans value (>= 64) during NFS mount, it causes a bit-shift operation to overflow, crashing the kernel.

Is CVE-2021-46952 being actively exploited?

No, this CVE is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are available. However, local attackers with mount privileges could trigger it via malformed mount parameters.

What versions of Kernel are affected by CVE-2021-46952?

Linux kernel versions 5.12.0 through 5.12.2 are vulnerable. Version 5.12.3 and all later versions contain the fix.

How do I check if my server is vulnerable to CVE-2021-46952?

Run: uname -r — if the output shows 5.12.0, 5.12.1, or 5.12.2, your system is vulnerable. For other kernel versions (5.11.x or earlier, 5.13+), you are not affected.

Does Defensia detect CVE-2021-46952?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-46952 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-2024-38623CVSS 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-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-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.
CVE-2022-48716CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ASoC: codecs: wcd938x: fix incorrect used of portid Mixer controls have the channel id in mixer->reg, which is not same as port id. port id should be derived from chan_info array. So fix this. Without this, its possible that we could corrupt struct wcd938x_sdw_priv by accessing port_map array out of range with channel id instead of port id.

References

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