high CVSS 7.8

CVE-2025-21671·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: zram: fix potential UAF of zram table If zram_meta_alloc failed early, it frees allocated zram->table without setting it NULL. Which will potentially cause zram_meta_free to access the table if user reset an failed and uninitialized device.

Severity
high
Software
Kernel
Fixed in
6.12.11
Published
2025-01-31

Affected versions

From: 6.12.7

Until: 6.12.11

Fixed in: 6.12.11

How to fix this CVE

Update your Linux kernel to version 6.12.11 or later to fix a use-after-free vulnerability in zram's memory allocation handler. This vulnerability allows potential unauthorized access and modification of kernel memory when zram device reset operations fail. Patch your system immediately to prevent memory corruption and privilege escalation attacks.

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 if the version is between 6.12.7 and 6.12.10 (vulnerable range)
  2. Verify zram is enabled: cat /proc/modules | grep zram — if zram is loaded, your system may expose this vulnerability
  3. Check kernel logs for zram_meta_alloc failures: dmesg | grep -i 'zram.*alloc' — look for memory allocation errors that could trigger the UAF condition
  4. Confirm the fix is applied: after patching, verify uname -r returns 6.12.11 or later, then reboot and re-run step 1

FAQ

What is CVE-2025-21671?

CVE-2025-21671 is a use-after-free vulnerability in the Linux kernel's zram module where a failed initialization leaves a dangling pointer in memory, allowing subsequent operations to access freed memory and potentially corrupt kernel state or escalate privileges.

Is CVE-2025-21671 being actively exploited?

No, according to CISA KEV data, CVE-2025-21671 is not currently being actively exploited in the wild, and no public proof-of-concept exploits are available.

What versions of Kernel are affected by CVE-2025-21671?

Linux kernel versions 6.12.7 through 6.12.10 are affected. Version 6.12.11 and later contain the fix.

How do I check if my server is vulnerable to CVE-2025-21671?

Run uname -r to check your kernel version. If the output shows 6.12.7, 6.12.8, 6.12.9, or 6.12.10, your system is vulnerable. Additionally, confirm zram is in use with: grep zram /proc/modules.

Does Defensia detect CVE-2025-21671?

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-2025-21671 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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