CVE-2025-21955

ksmbd: prevent connection release during oplock break notification

8.8 HighFix available

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: High

Exploit likelihood

0.50%Up 0.5 points since Apr 2, 2025

What each source reports

CVE List Score used 8.8

ksmbd: prevent connection release during oplock break notification

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: CVE-2025-21955
CVSS 3.1: 8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

EUVDEUVD-2025-9365 8.8

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: EUVD-2025-9365
CVSS 3.1: 8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

GitHub AdvisoriesGHSA-p2c4-6w6j-w378 5.5

In the Linux kernel, the following vulnerability has been resolved: ksmbd: prevent connection...

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: GHSA-p2c4-6w6j-w378
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

NVD 8.8

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: CVE-2025-21955
CVSS 3.1: 8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVBELL-CVE-2025-21955 5.5

Record: BELL-CVE-2025-21955
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-04

OSV 8.8

ksmbd: prevent connection release during oplock break notification

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: prevent connection release during oplock break notification

ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: CVE-2025-21955
CVSS 3.1: 8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

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OSVDEBIAN-CVE-2025-21955 5.5

In the Linux kernel, the following vulnerability has been resolved: ksmbd: prevent connection release during oplock break notification ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection.

Record: DEBIAN-CVE-2025-21955
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVOESA-2025-2120 8.0

kernel security update

The Linux Kernel, the operating system core itself.

Security Fix(es):

In the Linux kernel, the following vulnerability has been resolved:

gtp: Destroy device along with udp socket's netns dismantle.

gtp_newlink() links the device to a list in dev_net(dev) instead of src_net, where a udp tunnel socket is created.

Even when src_net is removed, the device stays alive on dev_net(dev). Then, removing src_net triggers the splat below. [0]

In this example, gtp0 is created in ns2, and the udp socket is created in ns1.

ip netns add ns1 ip netns add ns2 ip -n ns1 link add netns ns2 name gtp0 type gtp role sgsn ip netns del ns1

Let's link the device to the socket's netns instead.

Now, gtp_net_exit_batch_rtnl() needs another netdev iteration to remove all gtp devices in the netns.

[0]: ref_tracker: net notrefcnt@000000003d6e7d05 has 1/2 users at sk_alloc (./include/net/net_namespace.h:345 net/core/sock.c:2236) inet_create (net/ipv4/af_inet.c:326 net/ipv4/af_inet.c:252) __sock_create (net/socket.c:1558) udp_sock_create4 (net/ipv4/udp_tunnel_core.c:18) gtp_create_sock (./include/net/udp_tunnel.h:59 drivers/net/gtp.c:1423) gtp_create_sockets (drivers/net/gtp.c:1447) gtp_newlink (drivers/net/gtp.c:1507) rtnl_newlink (net/core/rtnetlink.c:3786 net/core/rtnetlink.c:3897 net/core/rtnetlink.c:4012) rtnetlink_rcv_msg (net/core/rtnetlink.c:6922) netlink_rcv_skb (net/netlink/af_netlink.c:2542) netlink_unicast (net/netlink/af_netlink.c:1321 net/netlink/af_netlink.c:1347) netlink_sendmsg (net/netlink/af_netlink.c:1891) ____sys_sendmsg (net/socket.c:711 net/socket.c:726 net/socket.c:2583) ___sys_sendmsg (net/socket.c:2639) __sys_sendmsg (net/socket.c:2669) do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)

WARNING: CPU: 1 PID: 60 at lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179) Modules linked in: CPU: 1 UID: 0 PID: 60 Comm: kworker/u16:2 Not tainted 6.13.0-rc5-00147-g4c1224501e9d #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 Workqueue: netns cleanup_net RIP: 0010:ref_tracker_dir_exit (lib/ref_tracker.c:179) Code: 00 00 00 fc ff df 4d 8b 26 49 bd 00 01 00 00 00 00 ad de 4c 39 f5 0f 85 df 00 00 00 48 8b 74 24 08 48 89 df e8 a5 cc 12 02 90 <0f> 0b 90 48 8d 6b 44 be 04 00 00 00 48 89 ef e8 80 de 67 ff 48 89 RSP: 0018:ff11000009a07b60 EFLAGS: 00010286 RAX: 0000000000002bd3 RBX: ff1100000f4e1aa0 RCX: 1ffffffff0e40ac6 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8423ee3c RBP: ff1100000f4e1af0 R08: 0000000000000001 R09: fffffbfff0e395ae R10: 0000000000000001 R11: 0000000000036001 R12: ff1100000f4e1af0 R13: dead000000000100 R14: ff1100000f4e1af0 R15: dffffc0000000000 FS: 0000000000000000(0000) GS:ff1100006ce80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f9b2464bd98 CR3: 0000000005286005 CR4: 0000000000771ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> ? __warn (kernel/panic.c:748) ? ref_tracker_dir_exit (lib/ref_tracker.c:179) ? report_bug (lib/bug.c:201 lib/bug.c:219) ? handle_bug (arch/x86/kernel/traps.c:285) ? exc_invalid_op (arch/x86/kernel/traps.c:309 (discriminator 1)) ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621) ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/spinlock_api_smp.h:151 kernel/locking/spinlock.c:194) ? ref_tracker_dir_exit (lib/ref_tracker.c:179) ? __pfx_ref_tracker_dir_exit (lib/ref_tracker.c:158) ? kfree (mm/slub.c:4613 mm/slub.c:4761) net_free (net/core/net_namespace.c:476 net/core/net_namespace.c:467) cleanup_net (net/core/net_namespace.c:664 (discriminator 3)) process_one_work…

Record: OESA-2025-2120
CVSS 3.1: 8.0 HighCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

OSVOESA-2025-2121 8.0

kernel security update

The Linux Kernel, the operating system core itself.

Security Fix(es):

In the Linux kernel, the following vulnerability has been resolved:

gtp: Destroy device along with udp socket's netns dismantle.

gtp_newlink() links the device to a list in dev_net(dev) instead of src_net, where a udp tunnel socket is created.

Even when src_net is removed, the device stays alive on dev_net(dev). Then, removing src_net triggers the splat below. [0]

In this example, gtp0 is created in ns2, and the udp socket is created in ns1.

ip netns add ns1 ip netns add ns2 ip -n ns1 link add netns ns2 name gtp0 type gtp role sgsn ip netns del ns1

Let's link the device to the socket's netns instead.

Now, gtp_net_exit_batch_rtnl() needs another netdev iteration to remove all gtp devices in the netns.

Record: OESA-2025-2121
CVSS 3.1: 8.0 HighCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

OSVOESA-2025-2122 8.0

kernel security update

The Linux Kernel, the operating system core itself.

Security Fix(es):

In the Linux kernel, the following vulnerability has been resolved:

gtp: Destroy device along with udp socket's netns dismantle.

gtp_newlink() links the device to a list in dev_net(dev) instead of src_net, where a udp tunnel socket is created.

Even when src_net is removed, the device stays alive on dev_net(dev). Then, removing src_net triggers the splat below. [0]

In this example, gtp0 is created in ns2, and the udp socket is created in ns1.

ip netns add ns1 ip netns add ns2 ip -n ns1 link add netns ns2 name gtp0 type gtp role sgsn ip netns del ns1

Let's link the device to the socket's netns instead.

Now, gtp_net_exit_batch_rtnl() needs another netdev iteration to remove all gtp devices in the netns.

Record: OESA-2025-2122
CVSS 3.1: 8.0 HighCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-02

OSVROOT-OS-DEBIAN-12-CVE-2025-21955 5.5

CVE-2025-21955 in linux - Patched by Root

Root has patched CVE-2025-21955 in the linux package for Root:Debian:12. Multiple fixed versions available.

Record: ROOT-OS-DEBIAN-12-CVE-2025-21955
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVROOT-OS-UBUNTU-2204-CVE-2025-21955 5.5

CVE-2025-21955 in linux - Patched by Root

Root has patched CVE-2025-21955 in the linux package for Root:Ubuntu:22.04. Multiple fixed versions available.

Record: ROOT-OS-UBUNTU-2204-CVE-2025-21955
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-06

OSVROOT-OS-UBUNTU-2404-CVE-2025-21955 5.5

CVE-2025-21955 in linux - Patched by Root

Root has patched CVE-2025-21955 in the linux package for Root:Ubuntu:24.04. Multiple fixed versions available.

Record: ROOT-OS-UBUNTU-2404-CVE-2025-21955
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-06

OSVUBUNTU-CVE-2025-21955 7.7

Record: UBUNTU-CVE-2025-21955
CVSS 4.0: 7.7 HighCVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS 3.1: 8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated: 2026-11-11

OSVMGASA-2025-0142 No score

Updated kernel, kmod-virtualbox & kmod-xtables-addons packages fix security vulnerabilities

Upstream kernel version 6.6.87 fixes bugs and vulnerabilities. The kmod-virtualbox and kmod-xtables-addons packages have been updated to work with this new kernel. For information about the vulnerabilities see the links.

Record: MGASA-2025-0142
Updated: 2026-11-02

OSVMGASA-2025-0146 No score

Updated kernel-linus packages fix security vulnerabilities

Vanilla upstream kernel version 6.6.88 fixes bugs and vulnerabilities. For information about the vulnerabilities see the links.

Record: MGASA-2025-0146
Updated: 2026-11-02

OSVUSN-7605-1 No score

linux, linux-aws, linux-gcp, linux-gcp-6.11, linux-hwe-6.11, linux-oracle, linux-raspi, linux-realtime vulnerabilities

It was discovered that the CIFS network file system implementation in the Linux kernel did not properly verify the target namespace when handling upcalls. An attacker could use this to expose sensitive information. (CVE-2025-2312)