CVE-2026-34890
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedImproper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Mark O’Donnell MSTW League Manager allows DOM-Based XSS.This issue affects MSTW League Manager: from n/a through 2.10.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceDOM-based Cross-site Scripting (XSS) vulnerability in MSTW League Manager plugin allows attackers to inject malicious JavaScript through unsanitized user input that gets dynamically inserted into the webpage DOM. This client-side attack executes in the victim's browser when they interact with the crafted URL or page content.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify MSTW League Manager plugin is installedAccess WordPress admin panel, navigate to Plugins > Installed Plugins, and locate 'MSTW League Manager' in the list. Note the installed version displayed.Affected if The plugin appears in the installed plugins list with any version.
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Identify the exact plugin version from filesIf admin access is unavailable, access the plugin directory via FTP or file manager at wp-content/plugins/mstw-league-manager/ and open the main PHP file (usually mstw-league-manager.php) to read the Version header in the plugin comments.Affected if A version number is found in the plugin files.
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Check for vulnerable JavaScript DOM handlingIf source code access is available, examine JavaScript files in the plugin's js/ folder for patterns where user-supplied data is directly inserted into the DOM using innerHTML, document.write, or similar methods without sanitization functions.Affected if Code patterns show user input being inserted into the DOM without encoding or sanitization.
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Inspect browser DOM for unsanitized outputWith the plugin active, use browser developer tools (F12), go to the Console tab, and navigate to plugin pages. Look for any URL parameters or form inputs that might reflect user data in the page HTML without encoding.Affected if User input appears in the page HTML or DOM without proper encoding when inspecting element source.
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Test for reflected user input in URLsIdentify plugin pages that accept URL parameters (such as team pages, league standings, or player profiles). Manually add a test string like <script>alert(1)</script> to URL parameters and observe if the script tag executes or appears in the page source.Affected if The test script tag executes in the browser or renders as literal text in the page.
If the MSTW League Manager plugin is installed and user-supplied input is rendered in the DOM without sanitization or encoding, the environment is affected by this DOM-based XSS vulnerability.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataImplement contextual output encoding and validate/sanitize all user-supplied data before inserting it into the DOM. Apply Content Security Policy (CSP) headers to restrict inline script execution. Update to the latest patched version when available.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-34890 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-34890 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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