What is CVE-2026-25539?

CVE-2026-25539 is a critical-severity vulnerability in B3log Siyuan, classified under Path Traversal. CVSS score: 9.1/10. Published 2026-02-04.

How severe is CVE-2026-25539?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Path Traversal in B3log Siyuan

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.

Vulnerability class: Path Traversal (Directory Traversal)

Published 2026-02-04 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.010 (62.5th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 62nd percentile — 62.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.010 · change: +0.000

Affected products

B3log Siyuan
Siyuan-Note Siyuan — versions < 3.5.5

Weakness classification (CWE)

CWE-22 — Path Traversal

References

github.com/siyuan-note/siyuan/security/advisories/GHSA-c4jr-5q7w-f6r9 (Exploit, Vendor Advisory)
github.com/siyuan-note/siyuan/commit/d7f790755edf8c78d2b4176171e5a0cdcd720feb (Patch)

Frequently asked questions

What is CVE-2026-25539?: CVE-2026-25539 is a critical-severity vulnerability in B3log Siyuan, classified under Path Traversal. CVSS score: 9.1/10. Published 2026-02-04.
How severe is CVE-2026-25539?: Critical severity. CVSS v3 base score is 9.1 out of 10.