CVE-2026-64380: In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length pars

Q: How do I fix CVE-2026-64380?

linux kernel: upgrade to 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-64380 being exploited?

CVE-2026-64380 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-64380 affect?

CVE-2026-64380 affects linux kernel. Severity is high (CVSS 8.2). In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length parsing posix_info_sid_size() reads sid[1] to obtain the subauthority count, but its existing boundary check still accepts buffers wi

Q: How urgent is CVE-2026-64380?

Priority 48/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

This month

HIGH 8.2REMOTEWATCHLISTUPGRADE

CVE-2026-64380 is a high-severity flaw (CVSS 8.2) affecting linux kernel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length parsing posix_info_sid_size() reads sid[1] to obtain the subauthority count, but its existing boundary check still accepts buffers with only one remaining byte. Require two bytes before reading sid[1] so all client paths that reuse the helper reject truncated POSIX SIDs safely.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-07-25
Last modified	2026-10-19

Publisher (CNA): kernel.org · Vendor: linux

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-25 10:17 UTCPublished CVE record published
2026-10-19 21:17 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 5.7 and < 5.10.261 · >= 5.11 and < 5.15.212 · >= 5.16 and < 6.1.178 · >= 6.2 and < 6.6.145 · >= 6.7 and < 6.12.96 · >= 6.13 and < 6.18.39 · >= 6.19 and < 7.1.4 · 7.2 rc1

Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-64380?

linux kernel: upgrade to 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4. Exact commands for each OS are on this page.

Is CVE-2026-64380 being exploited?

CVE-2026-64380 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-64380 affect?

CVE-2026-64380 affects linux kernel. Severity is high (CVSS 8.2). In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length parsing posix_info_sid_size() reads sid[1] to obtain the subauthority count, but its existing boundary check still accepts buffers wi

How urgent is CVE-2026-64380?

Priority 48/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities

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References

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