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VulnerabilityPublished Updated

CVE-2026-100646: siyuan · Origin Validation Error

Affects siyuanSource CVE Database V5

0
Compare

Public exploit available · CVSS 8.6 High : upgrade to 3.8.4 as a priority.

Data as of 10 Nov 2026, 23:24 UTC

CVSS 4.0 base score
8.6High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
Proof of concept is public or traded
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-09-30.

Patch
Available – fixed in 3.8.4
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

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

  1. Disclosed: evidence found.

    CVE published 26 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: evidence found.

    CISA SSVC: proof of concept public

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

Timeline

  1. CVE ID reserved

    by VulnCheck

    , 11 hours before disclosure

  2. CVE published

    on cve.org

    , t = 0

  3. CISA SSVC assessment

    proof of concept public

    , 4 days after disclosure

  4. In Threat Radar

    record ingested

    , 30 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA SSVC, the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

What to do

Upgrade siyuan to 3.8.4.

Affected software

ProductAffectedFixed in
siyuan-notesiyuanAffected
  • <3.8.4
Fixed in
  • 3.8.4
Gosiyuanpkg:golang/siyuanOther threatsAffected
  • <3.8.4
Fixed in
  • 3.8.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade SiYuan to version 3.8.4 or later, where this vulnerability is fixed. No other mitigation is indicated by the vendor advisory.

Description

SiYuan versions up to 3.8.3 have an origin validation flaw where the absence of the HTTP Origin header causes authentication checks to fail open. This allows cross-site GET requests from attacker-controlled pages to gain administrator privileges. The vulnerability also enables remote script execution within the SiYuan origin and exfiltration of the kernel API token. The issue is fixed in version 3.8.4.

References

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