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NVD / CVE Program· CNA VulnCheck

CVE-2026-100646: SiYuan before v3.8.4 Authentication Bypass via Missing Origin Header

Noroxi assessment

Priority: Monitor (action score 34/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.24% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No special conditions are required; it is repeatable.
  • Fixed version: siyuan-note siyuan 3.8.4.

Low priority for now. Upgrade to siyuan-note siyuan 3.8.4 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

SiYuan is a self-hosted personal knowledge management system. In versions up to and including 3.8.3, the kernel's authentication guards (CheckAuth in kernel/model/session.go and IsSessionOriginAllowed in kernel/util/net.go) fail open when the HTTP Origin header is absent, on the incorrect assumption that any browser-initiated cross-site request carries an Origin. Because browsers omit Origin on cross-site top-level GET navigations and no-cors GET subresource loads — and the session cookie is SameSite=Lax — a single cross-site GET issued from any attacker-controlled web page is granted RoleAdministrator, both on default installations with no access-authorization code and on password-protected instances with a live session. Combined with content-type sniffing on the /api/network/proxy endpoint, which allows attacker-controlled HTML to be served under SiYuan's own origin, this permits an unauthenticated remote attacker to execute arbitrary script in the SiYuan origin (http://127.0.0.1:6806), invoke administrator APIs, and exfiltrate the persistent kernel API token. This issue is fixed in version 3.8.4.

HighCVSS 8.6 · v4.0—No exploit Fix available
Published
Sep 26, 2026
Updated
Sep 30, 2026
EPSS
0.2% · 15th percentile

Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.6 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
proof of concept
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · VulnCheck
8.6
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-100646

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.

  • siyuan-note siyuan

    • 3.8.4not affected
    • before 3.8.4affected · semver

Same product

siyuan-note: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-66012SiYuan before v3.7.2 Unauthenticated Administrator Takeover via MCP
    40Plan
  • CVE-2026-72811SiYuan before v3.7.4 SQL Injection via backlink search
    39Monitor
  • CVE-2026-69085SiYuan before v3.7.3 SQL Injection via searchDocs
    39Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-100644Sep 26, 2026 · SiYuan before v3.8.4 SQL Injection via dailyNoteSavePath
    34Monitor
  • ← EarlierCVE-2026-100645Sep 26, 2026 · SiYuan 3.7.0 before 3.8.4 Stored XSS via Gallery Kanban
    34Monitor
  • Later →CVE-2026-101091Sep 28, 2026 · SiYuan before v3.8.4 SQL Injection via Block Query Embed
    28Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
siyuan-note siyuan3.8.4Vendor (CNA)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-5406994 days apartSiYuan: Unauthenticated Admin API Access via Blanket chrome-extension:// Origin Allowlist
    38Monitor
  • CVE-2026-1006420 days apartSiYuan v2.1.0 before v3.8.4 Cross-Site Request Forgery via CheckAuth
    28Monitor
  • CVE-2026-7480240 days apartSiYuan 3.7.3 Cross-Site WebSocket Hijacking via network proxy
    28Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

  • CVE-2026-1006450 days apartSiYuan 3.7.0 before 3.8.4 Stored XSS via Gallery Kanban
    34Monitor
  • CVE-2026-1006410 days apartSiYuan before v3.8.4 Stored XSS via Unescaped Flashcard Content
    34Monitor
  • CVE-2026-1006360 days apartSiYuan before v3.8.4 Path Traversal via exportBrowserHTML folder
    33Monitor
  • CVE-2026-1006370 days apartSiYuan before v3.8.4 Path Traversal via checkoutRepo sessionID
    33Monitor

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
P
Scope
X

Weakness class (CWE)

CWE-346 · Origin Validation Error

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. SSVC exploitation— → poc
  2. Fix✗ → ✓

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References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records