CVE-2026-31478: ksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len()

Severity: critical (CVSS 9.8 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 2026-10-19
Weakness: CWE-131

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len() After this commit (e2b76ab8b5c9 "ksmbd: add support for read compound"), response buffer management was changed to use dynamic iov array. In the new design, smb2_calc_max_out_buf_len() expects the second argument (hdr2_len) to be the offset of ->Buffer field in the response structure, not a hardcoded magic number. Fix the remaining call sites to use the correct offsetof() value.

Affected products

Linux kernel: from 5.15.145 before 5.15.203; from 6.1.71 before 6.1.168; from 6.6.1 before 6.6.131; from 6.7 before 6.12.80; from 6.13 before 6.18.21; from 6.19 before 6.19.11 — fixed in 5.15.203, 6.1.168, 6.12.80, 6.18.21, 6.19.11, 6.6.131

How to fix

Upgrade to a fixed version: Linux kernel 5.15.203, 6.1.168, 6.12.80, 6.18.21. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-31478 or the next vulnerability affects your stack