Security Digest · Vulnerability record
CVE-2026-25539: SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE
SiYuan is a personal knowledge management system.
CVSS 9.1 Critical EPSS 1.1% · p66
Should you act?
Critical, preconditions apply
Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.1%, percentile 66: FIRST’s model estimates a 1.1% chance of exploitation activity in the next 30 days, higher than 66% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs an account (high (admin)). Exposure depends on who can log in.
- Only applies if your dependency tree includes
github.com/siyuan-note/siyuan/kernel(Go) <= 0.0.0-20260126094835-d5d10dd41b0c, no fixed version listed. Check your lockfile, including transitive dependencies.
What it is
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 authorizedkeys, or shell configuration files. This issue has been patched in version 3.5.5.
From the GitHub advisory
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
Weakness type: CWE-22.
Product: github.com/siyuan-note/siyuan/kernel (Go) · Assigned by: GitHub_M · Published: 2026-02-04
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/siyuan-note/siyuan/kernel | <= 0.0.0-20260126094835-d5d10dd41b0c | none listed |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| siyuan-note | siyuan | < 3.5.5 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: high (admin)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 1.13% probability of exploitation activity in the next 30 days; percentile 66.
Timeline
- — GitHub-reviewed advisory GHSA-c4jr-5q7w-f6r9 published (critical)
- — CVE record published by GitHub_M
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-c4jr-5q7w-f6r9 github.com
- CVE.org record CVE-2026-25539 cve.org
- NVD entry CVE-2026-25539 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com