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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.1 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

EPSS

• CVE-2026-25539: 1.10% estimated exploitation activity in the next 30 days; percentile 65.82 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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 authorizedkeys, or shell configuration files. - Affected Version: 3.5.3 (and likely all prior versions) Details - Type: Improper Limitation of a Pathname to a Restricted Directory (CWE-22) - Location: kernel/api/file.go - copyFile function The src parameter is properly validated via model.GetAssetAbsPath(), but the dest parameter accepts any absolute path without validation, allowing files to be written outside the workspace directory. PoC Step 1: Upload malicious content to workspace Step 2: Copy to arbitrary location (e.g., /tmp) Response: {"code":0,"msg":"","data":null} Step 3: Verify file was written outside workspace Attack Scenarios | Target Path | Impact | |-------------|--------| | /etc/cron.d/backdoor | Scheduled…

Published by the source

29 Jan 2026, 15:15 UTC

Last modified by the source

5 Feb 2026, 00:36 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-c4jr-5q7w-f6r9

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# Patch Next advisory brief: CVE-2026-25539

Advisory: SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE
IDs: CVE-2026-25539, GHSA-c4jr-5q7w-f6r9
Record: https://patchnext.com/advisories/cve-2026-25539 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/siyuan-note/siyuan/kernel: affected <= 0.0.0-20260126094835-d5d10dd41b0c

## Suggested inspection (read-only)
- Go github.com/siyuan-note/siyuan/kernel: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/siyuan-note/siyuan/kernel.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c4jr-5q7w-f6r9 (GitHub-reviewed advisory GHSA-c4jr-5q7w-f6r9 lists affected ranges: Go github.com/siyuan-note/siyuan/kernel >=0 <=0.0.0-20260126094835-d5d10dd41b0c)

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