Linux Kernel up to 6.14-rc2 lib/refcount.c ax25_release reference count

Summaryinfo

A vulnerability identified as critical has been detected in Linux Kernel up to 6.1.128/6.6.78/6.12.15/6.13.3/6.14-rc2. The impacted element is the function ax25_release in the library lib/refcount.c. This manipulation causes reference count. This vulnerability appears as CVE-2025-21792. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.1.128/6.6.78/6.12.15/6.13.3/6.14-rc2 and classified as critical. Affected by this vulnerability is the function ax25_release in the library lib/refcount.c. The manipulation with an unknown input leads to a reference count vulnerability. The CWE definition for the vulnerability is CWE-911. The product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count. As an impact it is known to affect availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt If an AX25 device is bound to a socket by setting the SO_BINDTODEVICE socket option, a refcount leak will occur in ax25_release(). Commit 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()") added decrement of device refcounts in ax25_release(). In order for that to work correctly the refcounts must already be incremented when the device is bound to the socket. An AX25 device can be bound to a socket by either calling ax25_bind() or setting SO_BINDTODEVICE socket option. In both cases the refcounts should be incremented, but in fact it is done only in ax25_bind(). This bug leads to the following issue reported by Syzkaller: ================================================================ refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 1 PID: 5932 at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31 Modules linked in: CPU: 1 UID: 0 PID: 5932 Comm: syz-executor424 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31 Call Trace: __refcount_dec include/linux/refcount.h:336 [inline] refcount_dec include/linux/refcount.h:351 [inline] ref_tracker_free+0x710/0x820 lib/ref_tracker.c:236 netdev_tracker_free include/linux/netdevice.h:4156 [inline] netdev_put include/linux/netdevice.h:4173 [inline] netdev_put include/linux/netdevice.h:4169 [inline] ax25_release+0x33f/0xa10 net/ax25/af_ax25.c:1069 __sock_release+0xb0/0x270 net/socket.c:640 sock_close+0x1c/0x30 net/socket.c:1408 ... do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f ... ================================================================ Fix the implementation of ax25_setsockopt() by adding increment of refcounts for the new device bound, and decrement of refcounts for the old unbound device.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2025-21792 since 12/29/2024. The exploitation appears to be difficult. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 230879 (Linux Distros Unpatched Vulnerability : CVE-2025-21792), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.129, 6.6.79, 6.12.16, 6.13.4 or 6.14-rc3 eliminates this vulnerability. Applying the patch 90056ece99966182dc0e367f3fd2afab46ada847/94a0de224ed52eb2ecd4f4cb1b937b674c9fb955/b58f7ca86a7b8e480c06e30c5163c5d2f4e24023/470bda72fda0fcf54300466d70ce2de62f7835d2/bca0902e61731a75fc4860c8720168d9f1bae3b6 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (230879) and CERT Bund (WID-SEC-2025-0453). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Google Container-Optimized OS
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• Siemens SIMATIC S7
• RESF Rocky Linux
• Dell NetWorker
• Dell Avamar
• Red Hat OpenShift
• IBM QRadar SIEM
• SolarWinds Security Event Manager
• Dell PowerProtect Data Domain
• Open Source Linux Kernel
• IBM DataPower Gateway
• Dell Secure Connect Gateway
• Dell PowerScale OneFS
• Dell ECS

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.1.128
• 6.6.0
• 6.6.1
• 6.6.2
• 6.6.3
• 6.6.4
• 6.6.5
• 6.6.6
• 6.6.7
• 6.6.8
• 6.6.9
• 6.6.10
• 6.6.11
• 6.6.12
• 6.6.13
• 6.6.14
• 6.6.15
• 6.6.16
• 6.6.17
• 6.6.18
• 6.6.19
• 6.6.20
• 6.6.21
• 6.6.22
• 6.6.23
• 6.6.24
• 6.6.25
• 6.6.26
• 6.6.27
• 6.6.28
• 6.6.29
• 6.6.30
• 6.6.31
• 6.6.32
• 6.6.33
• 6.6.34
• 6.6.35
• 6.6.36
• 6.6.37
• 6.6.38
• 6.6.39
• 6.6.40
• 6.6.41
• 6.6.42
• 6.6.43
• 6.6.44
• 6.6.45
• 6.6.46
• 6.6.47
• 6.6.48
• 6.6.49
• 6.6.50
• 6.6.51
• 6.6.52
• 6.6.53
• 6.6.54
• 6.6.55
• 6.6.56
• 6.6.57
• 6.6.58
• 6.6.59
• 6.6.60
• 6.6.61
• 6.6.62
• 6.6.63
• 6.6.64
• 6.6.65
• 6.6.66
• 6.6.67
• 6.6.68
• 6.6.69
• 6.6.70
• 6.6.71
• 6.6.72
• 6.6.73
• 6.6.74
• 6.6.75
• 6.6.76
• 6.6.77
• 6.6.78
• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
• 6.12.7
• 6.12.8
• 6.12.9
• 6.12.10
• 6.12.11
• 6.12.12
• 6.12.13
• 6.12.14
• 6.12.15
• 6.13.0
• 6.13.1
• 6.13.2
• 6.13.3
• 6.14-rc1
• 6.14-rc2

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔍
• 🔍
• 🔍

CPE 2.2info

• 🔍
• 🔍
• 🔍

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Discussion