# CVE-2026-100635: SiYuan before v3.8.4 Authentication Bypass via Plaintext Session Cookie

> An on-path attacker can steal session cookies over HTTP to bypass authentication and access protected publish endpoints in SiYuan.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Sep 2026
- **Updated:** 27 Oct 2026
- **Also known as:** GHSA-7j37-4gq6-wm7m, GHSA-9f49-xx3h-chx9

## What is CVE-2026-100635?

CVE-2026-100635 is a high-severity authentication bypass vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SiYuan before v3.8.4 contains an authentication bypass vulnerability in the publish service where session cookies are issued without Secure or SameSite attributes over plaintext HTTP connections. An on-path attacker can observe a valid publish-visitor-session-id cookie from a Basic Auth exchange and replay it to access authenticated publish endpoints without knowing the account password.

Weakness: CWE-319 (Cleartext Transmission of Sensitive Information)

## Which versions are affected by CVE-2026-100635?


## How do I fix CVE-2026-100635?

No fix has been published for CVE-2026-100635 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100635 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100635 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100635 and fix it if it is affected.

What it is: CVE-2026-100635 is a high-severity authentication bypass vulnerability in siyuan-note siyuan, published on 26 Sep 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-2026-100635 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-2026-100635/ (Markdown: https://insights.sbomify.com/CVE-2026-100635/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100635
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100635
- OSV: https://osv.dev/vulnerability/CVE-2026-100635

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100635/
Summaries are generated and may contain mistakes; the official description above is the record.