CVE-2026-74521
Linux ksmbd GUID comparison bug allows SMB session spoofing.
Is CVE-2026-74521 being exploited?
Not confirmed. CVE-2026-74521 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.32% probability of exploitation in the next 30 days.
How severe is CVE-2026-74521?
CVE-2026-74521 is rated Critical with a CVSS score of 9.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-74521?
Yes. A fix has been recorded for CVE-2026-74521. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-74521 affect?
CVE-2026-74521 affects Linux kernel (ksmbd SMB3 multichannel), Linux distributions with vulnerable kernel versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-74521?
Update Linux kernel to patched version and restart ksmbd or reboot affected hosts.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attackers can spoof SMB ClientGUIDs to bypass SMB3 multichannel binding, enabling session hijack and unauthorized access to SMB shares.
Immediate action required
- affected>= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and < d535363299822c5caa543787b21bd5cfa3e41949
- affected>= e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and < e8bb506e6ef749ac0336f3e579d8d02396b7d832
- affected5.15
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.