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

Quick assessment

Affected
Go standard library os
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Windows 系统中，当 Root.Mkdir 或 Root.MkdirAll 的目标是一个指向空位置的符号链接（junction）时，该操作即使在目标位于根目录之外的情况下，仍可在符号链接的目标位置创建目录。此问题仅适用于路径的最后一个组件是符号链接的情况（例如 path/to/junction），而不适用于符号链接目标本身作为路径组件的情况（例如 path/junction/target）。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.21% · P10

Possible ATT&CK Techniques 1 AI

T1083 · File and Directory Discovery

Affected Version Matrix 4

VendorProduct Version RangeStatus
Go standard library internal/syscall/windows < 1.26.9 affected
1.27.0-0< 1.27.2 affected
Go standard library os < 1.26.9 affected
1.27.0-0< 1.27.2 affected
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I. Basic Information for CVE-2026-56857

Vulnerability Information
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Vulnerability Title
Root.Mkdir(All) can follow junctions out of the root on Windows in os
Source: CVE Program / CVE List V5
Vulnerability 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).
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Go standard library os 0 ~ 1.26.9 -
Go standard library internal/syscall/windows 0 ~ 1.26.9 -

II. Public POCs for CVE-2026-56857

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III. Intelligence Information for CVE-2026-56857

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Vendor Advisories for CVE-2026-56857 (1)

Security Blog Posts for CVE-2026-56857 (1)

Vendor Pages for CVE-2026-56857 (1)

Other References for CVE-2026-56857 (1)

Same Patch Batch · Go standard library · 2026-10-08 · 13 CVEs total

CVE-2026-94439 HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http
CVE-2026-94440 Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart
CVE-2026-94448 Reset context tracking on consecutive template expressions in html/template
CVE-2026-56866 HTTP/1 client connection desynchronization after CONNECT rejection in net/http
CVE-2026-78659 HTTP/2 server memory exhaustion due to Trailer headers in net/http
CVE-2026-78660 HTTP/2 transport accepts malformed framing-related headers in net/http
CVE-2026-78663 Double flow control refund on HTTP/2 server streams in net/http
CVE-2026-78667 Lack of limit on size of parsed Range headers in net/http
CVE-2026-78669 Excessive CPU consumption from repeated initial window changes in net/http
CVE-2026-97032 HTTP/2 server crash due to HPACK encoder race in net/http
CVE-2026-97030 Recognize yield as regexp preceder keyword in html/template
CVE-2026-97031 Reject malformed ECH outer extension references in crypto/tls

IV. Related Vulnerabilities

Same product: os
Same vendor: Go standard library

V. Comments for CVE-2026-56857

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