CVE-2026-45553

ui.restructured_text() renders reStructuredText server-side with Docutils without disabling file insertion directives.

When a NiceGUI application passes attacker-controlled content to ui.restructured_text(), an attacker can use standard Docutils directives (include, csv-table with :file:, raw with :file:) to read local files readable by the NiceGUI server process.

Applications that only pass trusted static strings to ui.restructured_text() are not affected.

Details

The affected component is the reStructuredText renderer:

• File: nicegui/elements/restructured_text.py
• Function: prepare_content()

prepare_content() renders user-supplied reStructuredText through Docutils:

html = publish_parts(
    remove_indentation(content),
    writer_name='html4',
    settings_overrides={'syntax_highlight': 'short'},
)

The Docutils call only sets syntax_highlight. It does not disable file insertion or raw directives, so Docutils processes directives that read local files and embed their contents into the generated HTML before it is returned to the browser. Frontend sanitization cannot prevent this because the file has already been read server-side.

A minimal vulnerable usage pattern is any page that forwards untrusted input into ui.restructured_text(), e.g. content taken from query parameters, form fields, or other user-controlled sources.

Local file disclosure. An attacker who can supply reStructuredText content can read files accessible to the NiceGUI server process. Depending on deployment, this may expose:

• application .env files
• database URLs, API tokens, session/storage secrets
• OAuth or cloud credentials
• Docker or Kubernetes mounted secrets
• application source files
• logs and other process-readable files

The confirmed impact is confidentiality loss through arbitrary local file read. Applications are only impacted when they pass untrusted or user-controlled reStructuredText into ui.restructured_text().

CVE-2026-45553 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. 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 (3.12.0); upgrading removes the vulnerable code path.

Kodem intelligence

Disable unsafe Docutils features in prepare_content():

html = publish_parts(
    remove_indentation(content),
    writer_name='html4',
    settings_overrides={
        'syntax_highlight': 'short',
        'file_insertion_enabled': False,
        'raw_enabled': False,
        '_disable_config': True,
    },
)

This blocks the include, csv-table :file:, and raw :file: directives as well as local docutils.conf overrides.

1. What is CVE-2026-45553? CVE-2026-45553 is a high-severity security vulnerability in nicegui (pip), affecting versions <= 3.11.1. It is fixed in 3.12.0.
2. How severe is CVE-2026-45553? CVE-2026-45553 has a CVSS score of 7.5 (High). 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 nicegui are affected by CVE-2026-45553? nicegui (pip) versions <= 3.11.1 is affected.
4. Is there a fix for CVE-2026-45553? Yes. CVE-2026-45553 is fixed in 3.12.0. Upgrade to this version or later.
5. Is CVE-2026-45553 exploitable, and should I be worried? Whether CVE-2026-45553 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-2026-45553 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-2026-45553? Upgrade nicegui to 3.12.0 or later.