CVE-2026-31432: ksmbd: fix OOB write in QUERY_INFO for compound requests

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-22 · updated 2026-10-30
Weakness: CWE-787

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix OOB write in QUERY_INFO for compound requests When a compound request such as READ + QUERY_INFO(Security) is received, and the first command (READ) consumes most of the response buffer, ksmbd could write beyond the allocated buffer while building a security descriptor. The root cause was that smb2_get_info_sec() checked buffer space using ppntsd_size from xattr, while build_sec_desc() often synthesized a significantly larger descriptor from POSIX ACLs. This patch introduces smb_acl_sec_desc_scratch_len() to accurately compute the final descriptor size beforehand, performs proper buffer checking with smb2_calc_max_out_buf_len(), and uses exact-sized allocation + iov pinning.

Affected products

Linux kernel: from 5.15.145 before 5.16; from 6.1.71 before 6.2; from 6.6 before 6.12.81; from 6.13 before 6.18.22; from 6.19 before 6.19.12; 7.0-rc1, 7.0-rc2, 7.0-rc3, 7.0-rc4, 7.0-rc5, 7.0-rc6 — fixed in 5.16, 6.2, 6.12.81, 6.18.22, 6.19.12
Linux: from 6.1.71 before 6.1.191; from 5.15.145 before 5.16 — fixed in 6.1.191, 5.16

How to fix

Upgrade to a fixed version: Linux kernel 5.16, 6.2, 6.12.81, 6.18.22; Linux 6.1.191, 5.16. Check the vendor advisory for mitigations.

References

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