# CVE-2026-63810: block: Avoid mounting the bdev pseudo-filesystem in userspace

Status: published. Published: 2026-07-19. Updated: 2026-11-10.

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

block: Avoid mounting the bdev pseudo-filesystem in userspace

The bdev pseudo-filesystem is an internal kernel filesystem with which
userspace should not interfere. Unregister it so that userspace cannot
even attempt to mount it.

This fixes a bug [1] that occurs when attempting to access files,
because the system call move_mount() uses pointers declared in the
inode_operations structure, which for the bdev pseudo-filesystem
are always equal to 0. `inode->i_op = &empty_iops;`

[1]

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 #PF: supervisor instruction fetch in kernel mode
 #PF: error_code(0x0010) - not-present page
 PGD 23380067 P4D 23380067 PUD 23381067 PMD 0
 Oops: 0010 [#1] PREEMPT SMP KASAN NOPTI
 CPU: 2 PID: 17125 Comm: syz-executor.0 Not tainted 6.1.155-syzkaller-00350-g84221fde2681 #0
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
 RIP: 0010:0x0

 Call Trace:
 <TASK>
 lookup_open.isra.0+0x700/0x1180 fs/namei.c:3460
 open_last_lookups fs/namei.c:3550 [inline]
 path_openat+0x953/0x2700 fs/namei.c:3780
 do_filp_open+0x1c5/0x410 fs/namei.c:3810
 do_sys_openat2+0x171/0x4d0 fs/open.c:1318
 do_sys_open fs/open.c:1334 [inline]
 __do_sys_openat fs/open.c:1350 [inline]
 __se_sys_openat fs/open.c:1345 [inline]
 __x64_sys_openat+0x13c/0x1f0 fs/open.c:1345
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x35/0x80 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 3d3fcf23993bb756de2f912ab631cfdcc4746554 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 99cde0a7b1e98fd3970aabef1300918e91698dd5 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 1a02a5028bd6dead1f8503854ef3168d651cd417 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 197971e6ffc0a6356b2ba2b22beb42bc0f7e412d (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 3804e6de30ae7b053d53341d9d6944356cf23b40 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 717f721eb67d2dacd3ed5f7495aef2f442e84ce4 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < f73aa66dffcb8e61e78f01b56163ec16a15d06d2 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.12 (affected); ≥ 0; < 2.6.12 (unaffected, semver); ≥ 5.15.212; ≤ 5.15.* (unaffected, semver); ≥ 6.1.178; ≤ 6.1.* (unaffected, semver); ≥ 6.6.145; ≤ 6.6.* (unaffected, semver); ≥ 6.12.95; ≤ 6.12.* (unaffected, semver); ≥ 6.18.38; ≤ 6.18.* (unaffected, semver); ≥ 7.1.3; ≤ 7.1.* (unaffected, semver); ≥ 7.2; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.21% as of 2026-11-09; percentile 10.81%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/3d3fcf23993bb756de2f912ab631cfdcc4746554 (CNA: Linux)

- https://git.kernel.org/stable/c/99cde0a7b1e98fd3970aabef1300918e91698dd5 (CNA: Linux)

- https://git.kernel.org/stable/c/1a02a5028bd6dead1f8503854ef3168d651cd417 (CNA: Linux)

- https://git.kernel.org/stable/c/197971e6ffc0a6356b2ba2b22beb42bc0f7e412d (CNA: Linux)

- https://git.kernel.org/stable/c/3804e6de30ae7b053d53341d9d6944356cf23b40 (CNA: Linux)

- https://git.kernel.org/stable/c/717f721eb67d2dacd3ed5f7495aef2f442e84ce4 (CNA: Linux)

- https://git.kernel.org/stable/c/f73aa66dffcb8e61e78f01b56163ec16a15d06d2 (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

- https://git.kernel.org/stable/c/197971e6ffc0a6356b2ba2b22beb42bc0f7e412d (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/1a02a5028bd6dead1f8503854ef3168d651cd417 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/3804e6de30ae7b053d53341d9d6944356cf23b40 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/3d3fcf23993bb756de2f912ab631cfdcc4746554 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/717f721eb67d2dacd3ed5f7495aef2f442e84ce4 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/99cde0a7b1e98fd3970aabef1300918e91698dd5 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/f73aa66dffcb8e61e78f01b56163ec16a15d06d2 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (0b142b55-0307-4c5a-b3c9-f314f3fb7c5e)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (0b142b55-0307-4c5a-b3c9-f314f3fb7c5e)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-63810; retrieved 2026-11-10; source updated 2026-11-10

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63810; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-63810; retrieved 2026-11-10; source updated Not reported

Revision: 9cc620a073864bd9fce5feeced105805796ca3019e2a3024fd94376ab5350b66

Canonical: https://y2.dev/cve/CVE-2026-63810

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