high CVSS 7.5 Public exploit available

CVE-2026-25732·Python vulnerability

NiceGUI is a Python-based UI framework. Prior to 3.7.0, NiceGUI's FileUpload.name property exposes client-supplied filename metadata without sanitization, enabling path traversal when developers use the pattern UPLOAD_DIR / file.name. Malicious filenames containing ../ sequences allow attackers to write files outside intended directories, with potential for remote code execution through application file overwrites in vulnerable deployment patterns. This design creates a prevalent security footgun affecting applications following common community patterns. Note: Exploitation requires application code incorporating file.name into filesystem paths without sanitization. Applications using fixed paths, generated filenames, or explicit sanitization are not affected. This vulnerability is fixed in 3.7.0.

Severity
high
Software
Python
Fixed in
3.7.0
Published
2026-02-06

Affected versions

Until: 3.7.0

Fixed in: 3.7.0

How to fix this CVE

Update NiceGUI to version 3.7.0 or later, which sanitizes the FileUpload.name property to prevent path traversal attacks. If you are using NiceGUI in your Python applications, review any code that directly uses file.name in filesystem operations and implement explicit filename validation. Applications that already generate filenames server-side or use fixed upload directories are not vulnerable to this issue.

sudo dnf update python3-nicegui

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST.*filename=.*\.\.[\\/]|GET.*upload.*filename=%2e%2e[\\/]|multipart.*filename="[^"]*\.\.[\\/]

WAF mitigation (if patching is not yet possible)

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

Implement WAF rules to block upload requests with filenames containing '../', '..\', '%2e%2e', or similar path traversal patterns. Additionally, reject any uploaded filename parameter that does not match a whitelist of safe characters (alphanumeric, dash, underscore, dot only).

How to check if you are affected

  1. Step 1: Check NiceGUI version: python3 -c "import nicegui; print(nicegui.__version__)"
  2. Step 2: Search your application codebase for patterns matching 'UPLOAD_DIR / file.name' or similar direct concatenation: grep -r "file\.name" --include="*.py" /path/to/app
  3. Step 3: Review web server access logs for requests containing '../' or '..%2f' in filename parameters: grep -E '(\.\.%2f|\.\./|%252e%252e)' /var/log/nginx/access.log
  4. Step 4: Verify the fix by confirming NiceGUI version is 3.7.0 or higher: python3 -m pip show nicegui | grep Version

Indicators of compromise

  • Filenames containing '../' or '..\'in HTTP requests
  • Filenames with URL-encoded traversal: %2e%2e%2f or %252e%252e%252f
  • Successful writes to directories outside configured UPLOAD_DIR
  • Unexpected .pyc or .py files in parent directories of upload location

FAQ

What is CVE-2026-25732?

This vulnerability exists in NiceGUI's FileUpload component, which fails to sanitize uploaded filenames. Attackers can craft malicious filenames with path traversal sequences (../) to write files outside the intended upload directory, potentially enabling code execution through application file overwrites.

Is CVE-2026-25732 being actively exploited?

CVE-2026-25732 is not currently listed on CISA's KEV catalog, but public exploit code is available, indicating the vulnerability is well-understood and could be leveraged opportunistically against unpatched systems.

What versions of NiceGUI are affected by CVE-2026-25732?

All versions of NiceGUI prior to 3.7.0 are affected. The vulnerability was introduced in the FileUpload implementation and remains present until the 3.7.0 release.

How do I check if my server is vulnerable to CVE-2026-25732?

Run 'python3 -c "import nicegui; print(nicegui.__version__)"' and verify the version is 3.7.0 or later. Additionally, inspect your application code for any direct use of the file.name property in path operations without explicit sanitization.

Does Defensia detect CVE-2026-25732?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If NiceGUI is installed on a monitored server, CVE-2026-25732 will appear in your dashboard with remediation steps.

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References

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