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.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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 | 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 include 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.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
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 SiYuan has an Arbitrary File Read in its Desktop Publish Service
- CVE-2026-33669 SiYuan has Arbitrary Document Reading within the Publishing Service
- CVE-2026-33670 SiYuan has directory traversal within its publishing service
- CVE-2026-32767 SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API
- CVE-2024-53504 SQL injection in n/a
Sources
Also known as GHSA-c4jr-5q7w-f6r9, GO-2026-4387.