CVE Catalog

CVE-2026-63909

HighCVSS 8.1
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.63%

46th percentile - higher than 46% of all known CVEs

Summary

In the Linux kernel's ksmbd filesystem, a regression causes an out-of-bounds (OOB) read in the ACE-walk loop of smb_check_perm_dacl(). The flaw stems from a transposed bounds check that never breaks the loop, allowing a 2-byte heap OOB read past the allocated pntsd buffer during SMB2_CREATE operations.

Risk Assessment

This vulnerability allows a remote attacker to read kernel memory beyond the allocated buffer, potentially leading to information disclosure or system instability.

Recommendation

Immediately update the Linux kernel to a version containing the fix that restores proper bounds checking (requiring at least 16 bytes) in smb_check_perm_dacl().

Other vulnerabilities in Linux kernel

See all
Original NVD description (English source)

In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().

Vulnerability data from NVD (NIST) · CISA KEV · EPSS