# CVE-2026-72809: SiYuan before v3.7.4 Authentication Bypass via Localhost Trust

> Remote attackers can gain admin access via localhost trust bypass in SiYuan when using a fixed-port reverse proxy bound to a network interface.

- **Severity:** High 7.1 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Aug 2026
- **Updated:** 14 Aug 2026
- **Also known as:** GHSA-3mp7-4rh5-jrv9, GO-2026-6386

## What is CVE-2026-72809?

CVE-2026-72809 is a high-severity authentication bypass vulnerability in siyuan-note siyuan, published on 12 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

SiYuan versions <= v3.7.2 (patched in v3.7.4) contain an authentication bypass vulnerability in the kernel's CheckAuth function, which grants the administrator role (RoleAdministrator) to any request whose RemoteAddr is loopback (127.0.0.1) for a specific set of endpoints (including /api/system/exit, getNetwork, getWorkspaceInfo, /assets/*, and /export/*). These localhost bypasses sit outside the access auth code gate, so they apply even when an access auth code is configured. Because the fixed-port reverse proxy forwards requests to the kernel over loopback without injecting an authentication token and does not configure trusted proxies, a request forwarded through this proxy reaches the kernel with RemoteAddr = 127.0.0.1. If the fixed-port proxy is bound to a network interface, this could allow a remote unauthenticated attacker to obtain admin access on the affected endpoints; however, per the advisory this remote forwarding behavior was established only by code inspection and was not reproduced end-to-end.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-72809?

3 open source packages ship an affected version, including github.com/siyuan-note/siyuan/kernel.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260723031701-9c16e9851f0b |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260723031701-9c16e9851f0b |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260723031701-9c16e9851f0b |

## How do I fix CVE-2026-72809?

Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260723031701-9c16e9851f0b or later.

## Is CVE-2026-72809 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-72809 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72809 and fix it if it is affected.

What it is: CVE-2026-72809 is a high-severity authentication bypass vulnerability in siyuan-note siyuan, published on 12 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-72809 exists.

Affected packages and fixed versions:
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260723031701-9c16e9851f0b
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260723031701-9c16e9851f0b
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260723031701-9c16e9851f0b

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72809/ (Markdown: https://insights.sbomify.com/CVE-2026-72809/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72809
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72809
- OSV: https://osv.dev/vulnerability/CVE-2026-72809

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72809/
Summaries are generated and may contain mistakes; the official description above is the record.