CVE-2025-12799
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 · uneditedA flaw was found in Jastow. Jastow is vulnerable to Cross-Site Scripting (XSS) attack. If using a set of combined configuration to allow unescaped characters in URL with embedded Undertow and Jastow, a server might be vulnerable to improper input handling.
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 confidenceJastow, a template engine for Undertow/JBoss, contains a Cross-Site Scripting (XSS) vulnerability stemming from improper input handling when a specific configuration combination allows unescaped characters in URLs. The vulnerability requires both Undertow and Jastow to be configured in a way that permits unescaped input, enabling attackers to inject malicious scripts via URL parameters.
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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
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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Identify Jastow deploymentSearch for jastow JAR files in the application library directory (e.g., WEB-INF/lib, classpath) or check build dependencies for jastow inclusionAffected if Jastow is present in the application runtime
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Confirm Undertow as the web serverCheck if Undertow is used as the embedded web server (look for undertow-core JAR, or in standalone.xml/configuration for JBoss/WildFly)Affected if Undertow serves as the HTTP server handling requests to Jastow
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Inspect URL character escaping configurationReview Undertow configuration files (undertow.xml, standalone.xml, or programmatic configuration) for settings controlling URL character handling - look for 'allowEncodedSlash', 'decodeDirect', or similar URL encoding settingsAffected if Undertow is configured to allow unescaped characters in URLs without proper validation
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Verify Jastow template rendering for URL parametersExamine Jastow templates (.jastow files) that process request URL parameters - check if parameters are rendered directly into HTML output without escaping (search for ${param.X} or similar constructs)Affected if Templates render URL parameters directly without HTML encoding
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Test for XSS via URL parameter injectionDeploy a simple test with a benign script payload in a URL parameter (e.g., ?test=<script>alert(1)</script>) and verify if the payload is executed in the response when rendered by JastowAffected if URL parameter values appear unescaped in the HTTP response
The environment is affected if Jastow renders URL parameters in templates while Undertow allows unescaped characters in URLs, enabling XSS injection via crafted URLs.
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 dataFix the input handling in Jastow to properly escape or validate user-supplied input in URLs, and review Undertow configuration to ensure proper character escaping is enabled.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-12799 — 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-2025-12799 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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