CVE-2026-31809
CVE-2026-31809 is a medium-severity vulnerability in B3log Siyuan with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.
Key facts
- Severity: Medium (CVSS 3.x base score 6.1)
- CVSS v4: 6.4
- EPSS exploit prediction: 1% (40th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-10896
- Weakness: CWE-79
- Affected product: B3log Siyuan
- Published:
- Last modified:
Description
SiYuan is a personal knowledge management system. Prior to 3.5.10, SiYuan's SVG sanitizer (SanitizeSVG) checks href attributes for the javascript: prefix using strings.HasPrefix(). However, inserting ASCII tab (	), newline ( ), or carriage return ( ) characters inside the javascript: string bypasses this prefix check. Browsers strip these characters per the WHATWG URL specification before parsing the URL scheme, so the JavaScript still executes. This allows an attacker to inject executable JavaScript into the unauthenticated /api/icon/getDynamicIcon endpoint, creating a reflected XSS. This is a second bypass of the fix for CVE-2026-29183 (fixed in v3.5.9). This vulnerability is fixed in 3.5.10.
Frequently asked questions
- What is CVE-2026-31809?
- SiYuan is a personal knowledge management system. Prior to 3.5.10, SiYuan's SVG sanitizer (SanitizeSVG) checks href attributes for the javascript: prefix using strings.HasPrefix(). However, inserting ASCII tab (	), newline ( ), or carriage return ( ) characters inside the javascript: string bypasses this prefix check. Browsers strip these characters per the WHATWG URL specification before parsing the URL scheme, so the JavaScript still executes. This allows an attacker to inject executable JavaScript into the unauthenticated /api/icon/getDynamicIcon endpoint, creating a reflected XSS. This is a second bypass of the fix for CVE-2026-29183 (fixed in v3.5.9). This vulnerability is fixed in 3.5.10.
- How severe is CVE-2026-31809?
- CVE-2026-31809 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
- Is CVE-2026-31809 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (40th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-31809?
- CVE-2026-31809 affects B3log Siyuan. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-31809?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-31809 have an EU (EUVD) identifier?
- Yes. CVE-2026-31809 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10896.
- When was CVE-2026-31809 published?
- CVE-2026-31809 was published on 2026-03-10 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:b3log:siyuan:*:*:*:*:*:*:*:*
More vulnerabilities in B3log Siyuan
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