high CVSS 7.8

CVE-2025-21863·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: io_uring: prevent opcode speculation sqe->opcode is used for different tables, make sure we santitise it against speculations.

Severity
high
Software
Kernel
Fixed in
6.13.5
Published
2025-03-12

Affected versions

From: 6.13

Until: 6.13.5

Fixed in: 6.13.5

How to fix this CVE

Update your Linux kernel to version 6.13.5 or later to patch the io_uring opcode speculation vulnerability. This fix prevents potential information disclosure and privilege escalation through speculative execution attacks on the io_uring subsystem. Apply the kernel update through your distribution's package manager and reboot your system to complete the remediation.

sudo dnf update kernel kernel-headers && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your current kernel version by running: uname -r
  2. Verify if your version falls in the vulnerable range (6.13.0 to 6.13.4) by comparing output against the affected versions list
  3. Examine kernel audit logs for unexpected io_uring syscall sequences: sudo ausearch -m SYSCALL -k io_uring 2>/dev/null | grep -i opcode
  4. After patching, confirm the new kernel version loads: uname -r (should show 6.13.5 or higher) and verify with: sudo dmesg | grep 'Linux version'

FAQ

What is CVE-2025-21863?

CVE-2025-21863 is a high-severity Linux kernel vulnerability affecting the io_uring subsystem where the opcode field is insufficiently protected against speculative execution attacks, allowing local attackers with low privileges to read kernel memory or escalate privileges.

Is CVE-2025-21863 being actively exploited?

No, according to CISA's Known Exploited Vulnerabilities catalog, CVE-2025-21863 is not currently being actively exploited in the wild, and no public exploit code is available.

What versions of Kernel are affected by CVE-2025-21863?

Linux kernel versions 6.13.0 through 6.13.4 are vulnerable. The vulnerability is fixed in kernel version 6.13.5 and later.

How do I check if my server is vulnerable to CVE-2025-21863?

Run uname -r to check your kernel version. If the output shows a version between 6.13.0 and 6.13.4 inclusive, your system is vulnerable and requires immediate kernel update.

Does Defensia detect CVE-2025-21863?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2025-21863 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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