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Vulnerability · Published Oct 8, 2026 · Assigned by Go

CVE-2026-56857Root.Mkdir(All) can follow junctions out of the root on Windows in os

Critical 9.8

In plain English

A critical-severity security flaw in internal/syscall/windows from Go standard library. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.6%top 53.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target).

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.24docker29.9.0-r0ALPINE-CVE-2026-56857
Alpine:v3.24go1.26.9-r0ALPINE-CVE-2026-56857
Gostdlib1.26.9, 1.27.2GO-2026-6604
Ubuntu:22.04:LTSgolang-1.17no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.18no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.20no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.21no fix listedUBUNTU-CVE-2026-56857
Ubuntu:24.04:LTSgolang-1.21no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.23no fix listedUBUNTU-CVE-2026-56857
Ubuntu:24.04:LTSgolang-1.23no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.04:LTSgolang-1.23no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.24no fix listedUBUNTU-CVE-2026-56857
Ubuntu:24.04:LTSgolang-1.24no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.04:LTSgolang-1.24no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.25no fix listedUBUNTU-CVE-2026-56857
Ubuntu:24.04:LTSgolang-1.25no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.04:LTSgolang-1.25no fix listedUBUNTU-CVE-2026-56857
Ubuntu:22.04:LTSgolang-1.26no fix listedUBUNTU-CVE-2026-56857
Ubuntu:24.04:LTSgolang-1.26no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.04:LTSgolang-1.26no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.10golang-1.26no fix listedUBUNTU-CVE-2026-56857
Ubuntu:26.10golang-1.27no fix listedUBUNTU-CVE-2026-56857

Affected products (as reported)

VendorProductVersions
Go standard library os 0 – before 1.26.91.27.0-0 – before 1.27.2
Go standard library internal/syscall/windows 0 – before 1.26.91.27.0-0 – before 1.27.2

Weakness: CWE-1386 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References