# CVE-2026-25539: SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE

> Authenticated attackers can write files to arbitrary locations via the copyFile API, enabling remote code execution by modifying system files.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Feb 2026
- **Updated:** 5 Feb 2026
- **Also known as:** GHSA-c4jr-5q7w-f6r9, GO-2026-4387

## What is CVE-2026-25539?

CVE-2026-25539 is a critical path traversal vulnerability in B3log Siyuan, published on 4 Feb 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official 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.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-25539?

3 open source packages ship an affected version, including github.com/siyuan-note/siyuan/kernel. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | None |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions to 0.0.0-20260126094835-d5d10dd41b0c | None |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions to 0.0.0-20260126094835-d5d10dd41b0c | None |

Products: B3log Siyuan.

## How do I fix CVE-2026-25539?

No fix has been published for CVE-2026-25539 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-25539 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25539 exists.

## Other vulnerabilities in B3log Siyuan

- [CVE-2026-32938](https://insights.sbomify.com/CVE-2026-32938/): SiYuan has an Arbitrary File Read in its Desktop Publish Service (critical 9.9)
- [CVE-2026-33669](https://insights.sbomify.com/CVE-2026-33669/): SiYuan has Arbitrary Document Reading within the Publishing Service (critical 9.8)
- [CVE-2026-33670](https://insights.sbomify.com/CVE-2026-33670/): SiYuan has directory traversal within its publishing service (critical 9.8)
- [CVE-2026-32767](https://insights.sbomify.com/CVE-2026-32767/): SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API (critical 9.8)
- [CVE-2024-53504](https://insights.sbomify.com/CVE-2024-53504/): SQL injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25539 and fix it if it is affected.

What it is: CVE-2026-25539 is a critical path traversal vulnerability in B3log Siyuan, published on 4 Feb 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25539 exists.

Affected packages and fixed versions:
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; no fix listed
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions up to 0.0.0-20260126094835-d5d10dd41b0c; no fix listed
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions up to 0.0.0-20260126094835-d5d10dd41b0c; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-25539/ (Markdown: https://insights.sbomify.com/CVE-2026-25539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25539
- OSV: https://osv.dev/vulnerability/CVE-2026-25539

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25539/
Summaries are generated and may contain mistakes; the official description above is the record.