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CRITICAL

CVE-2026-25539

SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE

CVSS v3

9.1

CRITICAL

EPSS Score

1.0 %

exploit probability, as of 2026-09-25

CISA KEV

No

known exploited

Exploitation

poc

SSVC status

Description

SiYuan is a personal knowledge management system. Prior to version 3.5.5, the /api/file/copyFile endpoint does not validate the dest parameter, allowing authenticated users to write files to arbitrary locations on the filesystem. This can lead to Remote Code Execution (RCE) by writing to sensitive locations such as cron jobs, SSH authorized_keys, or shell configuration files. This issue has been patched in version 3.5.5.

Technical details

Published
2026-02-04
Last Modified
2026-02-11

Frequently asked questions

What is CVE-2026-25539?

SiYuan is a personal knowledge management system. Prior to version 3.5.5, the /api/file/copyFile endpoint does not validate the dest parameter, allowing authenticated users to write files to arbitrary locations on the filesystem. This can lead to Remote Code Execution (RCE) by writing to sensitive locations such as cron jobs, SSH authorized_keys, or shell configuration files. This issue has been patched in version 3.5.5.

Is CVE-2026-25539 actively exploited?

A proof-of-concept exploit exists for CVE-2026-25539, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-25539?

CVE-2026-25539 has a CVSS v3 base score of 9.1 (CRITICAL severity).

Is CVE-2026-25539 affecting your environment?

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