# CVE-2026-74905: SiYuan before v3.7.4 SSRF via IPv6 Transition Address Bypass

> Authenticated attackers can bypass SSRF protections in SiYuan's SafeMode to access internal services and cloud metadata via IPv6 transition addresses.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** GHSA-qrjw-gxw5-x7q9

## What is CVE-2026-74905?

CVE-2026-74905 is a medium-severity server-side request forgery vulnerability in siyuan-note siyuan, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SiYuan before v3.7.4 contains a server-side request forgery (SSRF) vulnerability in the isPrivateIP function in kernel/util/net.go, used by SSRFSafeDialer to enforce SSRF protection in SafeMode. The function only checks for loopback, link-local unicast, private, and unspecified addresses and does not recognize IPv6 transition addresses (NAT64 64:ff9b::/96, 6to4 2002::/16, Teredo 2001::/32) that embed private IPv4 destinations. When SafeMode is enabled, an authenticated attacker can bypass the SSRF guard via the network forward proxy, WebSocket proxy, or SSE proxy endpoints by supplying a URL whose hostname resolves to such a transition address, reaching internal services and cloud metadata endpoints (e.g., 169.254.169.254). Because the forward proxy returns the full response body, this is a full-read SSRF that can be used to steal instance credentials, reach internal services, and port-scan internal infrastructure.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-74905?


## How do I fix CVE-2026-74905?

No fix has been published for CVE-2026-74905 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-74905 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-74905 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74905 and fix it if it is affected.

What it is: CVE-2026-74905 is a medium-severity server-side request forgery vulnerability in siyuan-note siyuan, published on 18 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-74905 exists.

Affected product: siyuan-note siyuan. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-74905/ (Markdown: https://insights.sbomify.com/CVE-2026-74905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74905
- OSV: https://osv.dev/vulnerability/CVE-2026-74905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74905/
Summaries are generated and may contain mistakes; the official description above is the record.