CVE-2026-23249

What it is

In the Linux kernel, the following vulnerability has been resolved: xfs: check for deleted cursors when revalidating two btrees The free space and inode btree repair functions will rebuild both btrees at the same time, after which it needs to evaluate both btrees to confirm that the corruptions are gone. However, Jiaming Zhang ran syzbot and produced a crash in the second xchk_allocbt call. His root-cause analysis is as follows (with minor corrections): In xrep_revalidate_allocbt(), xchk_allocbt() is called twice (first for BNOBT, second for CNTBT). The cause of this issue is that the first call nullified the cursor required by the second call. Let's first enter xrep_revalidate_allocbt() via following call chain: xfs_file_ioctl() -> xfs_ioc_scrubv_metadata() -> xfs_scrub_metadata() -> `sc->ops->repair_eval(sc)` -> xrep_revalidate_allocbt() xchk_allocbt() is called twice in this function. In the first call: /* Note that sc->sm->sm_type is XFS_SCRUB_TYPE_BNOPT now */ xchk_allocbt() -> xchk_btree() -> `bs->scrub_rec(bs, recp)` -> xchk_allocbt_rec() -> xchk_allocbt_xref() -> xchk_allocbt_xref_other() since sm_type is XFS_SCRUB_TYPE_BNOBT, pur is set to &sc->sa.cnt_cur. Kernel called xfs_alloc_get_rec() and returned -EFSCORRUPTED. Call chain: xfs_alloc_get_rec() -> xfs_btree_get_rec() -> xfs_btree_check_block() -> (XFS_IS_CORRUPT || XFS_TEST_ERROR), the former is false and the latter is true, return -EFSCORRUPTED. This should be caused by ioctl$XFS_IOC_ERROR_INJECTION I guess. Back to xchk_allocbt_xref_other(), after receiving -EFSCORRUPTED from xfs_alloc_get_rec(), kernel called xchk_should_check_xref(). In this function, *curpp (points to sc->sa.cnt_cur) is nullified. Back to xrep_revalidate_allocbt(), since sc->sa.cnt_cur has been nullified, it then triggered null-ptr-deref via xchk_allocbt() (second call) -> xchk_btree(). So. The bnobt revalidation failed on a cross-reference attempt, so we deleted the cntbt cursor, and then crashed when we tried to revalidate the cntbt. Therefore, check for a null cntbt cursor before that revalidation, and mark the repair incomplete. Also we can ignore the second tree entirely if the first tree was rebuilt but is already corrupt. Apply the same fix to xrep_revalidate_iallocbt because it has the same problem.

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of service disruption.

Exploit odds

0.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-03-18 18:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-11-05 22:18 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.1% in the next 30 days (EPSS).
• Severity: 5.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-03-18 18:16 UTC

Last modified

2026-11-05 22:18 UTC

Exploit probability

0.1% · EPSS, next 30 days

Weakness

CWE-476 · NULL pointer dereference

Record status

Analyzed

Affected

• Linux Kernel < 6.12.75
• Linux Kernel < 6.18.16
• Linux Kernel < 6.19.6

Attack profile CVSS 3.1 · 5.5

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

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