Vulnerability-Lookup

CVE-2026-39844 (GCVE-0-2026-39844)

Vulnerability from cvelistv5 – Published: 2026-04-08 20:13 – Updated: 2026-04-09 16:17

Title

NiceGUI has a Path Traversal in NiceGUI Upload Filename on Windows via Backslash Bypass of PurePosixPath Sanitization

Summary

NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename. Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows. This vulnerability is fixed in 3.10.0.

Severity

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-09 14:55 UTC

CWE

CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7993 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/zauberzeug/nicegui/security/ad…	x_refsource_CONFIRM
https://github.com/zauberzeug/nicegui/commit/d38a…	x_refsource_MISC
https://github.com/zauberzeug/nicegui/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
zauberzeug	nicegui	Affected: < 3.10.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-39844

Vulnerability from fkie_nvd - Published: 2026-04-08 21:16 - Updated: 2026-07-24 21:10

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/zauberzeug/nicegui/commit/d38a702e3af2da5b0708f689be8d71413fc77056	Patch
security-advisories@github.com	https://github.com/zauberzeug/nicegui/releases/tag/v3.10.0	Release Notes
security-advisories@github.com	https://github.com/zauberzeug/nicegui/security/advisories/GHSA-w8wv-vfpc-hw2w	Vendor Advisory

Impacted products

	Vendor	Product	Version
	zauberzeug	nicegui	*
	microsoft	windows	-

JSON

To clipboard

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  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-22"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-W8WV-VFPC-HW2W

Vulnerability from github – Published: 2026-04-08 15:04 – Updated: 2026-04-09 14:28

Summary

NiceGUI: Upload filename sanitization bypass via backslashes allows path traversal on Windows

Details

Summary

The upload filename sanitization introduced in GHSA-9ffm-fxg3-xrhh uses PurePosixPath(filename).name to strip path components. Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename.

Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows.

Details

The sanitization in nicegui/elements/upload_files.py uses:

filename = PurePosixPath(upload.filename or '').name

PurePosixPath treats backslashes as literal characters, not path separators:

>>> PurePosixPath('..\\..\\secret\\evil.txt').name
'..\\..\\secret\\evil.txt'  # Not stripped!

When this filename is used in a path operation on Windows (e.g., Path('uploads') / file.name), Windows Path interprets backslashes as directory separators, resolving the path outside the intended directory.

Impact

On Windows deployments of NiceGUI applications that use file.name in path construction:

Arbitrary file write outside the intended upload directory
Potential remote code execution through overwriting application files or placing executables in known locations
Data integrity loss through overwriting existing files

Linux and macOS are not affected, as they treat backslashes as literal filename characters.

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.9.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "nicegui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-39844"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-08T15:04:13Z",
    "nvd_published_at": "2026-04-08T21:16:59Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe upload filename sanitization introduced in GHSA-9ffm-fxg3-xrhh uses `PurePosixPath(filename).name` to strip path components. Since `PurePosixPath` only recognizes forward slashes (`/`) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (`\\`) in the upload filename.\n\nApplications that construct file paths using `file.name` (a pattern demonstrated in NiceGUI\u0027s bundled examples) are vulnerable to arbitrary file write on Windows.\n\n### Details\n\nThe sanitization in `nicegui/elements/upload_files.py` uses:\n\n```python\nfilename = PurePosixPath(upload.filename or \u0027\u0027).name\n```\n\n`PurePosixPath` treats backslashes as literal characters, not path separators:\n\n```python\n\u003e\u003e\u003e PurePosixPath(\u0027..\\\\..\\\\secret\\\\evil.txt\u0027).name\n\u0027..\\\\..\\\\secret\\\\evil.txt\u0027  # Not stripped!\n```\n\nWhen this filename is used in a path operation on Windows (e.g., `Path(\u0027uploads\u0027) / file.name`), Windows `Path` interprets backslashes as directory separators, resolving the path outside the intended directory.\n\n### Impact\n\nOn Windows deployments of NiceGUI applications that use `file.name` in path construction:\n\n- **Arbitrary file write** outside the intended upload directory\n- **Potential remote code execution** through overwriting application files or placing executables in known locations\n- **Data integrity loss** through overwriting existing files\n\nLinux and macOS are not affected, as they treat backslashes as literal filename characters.",
  "id": "GHSA-w8wv-vfpc-hw2w",
  "modified": "2026-04-09T14:28:46Z",
  "published": "2026-04-08T15:04:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-w8wv-vfpc-hw2w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39844"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/commit/d38a702e3af2da5b0708f689be8d71413fc77056"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/zauberzeug/nicegui"
    },
    {
      "type": "WEB",
      "url": "https://github.com/zauberzeug/nicegui/releases/tag/v3.10.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "NiceGUI: Upload filename sanitization bypass via backslashes allows path traversal on Windows"
}

PYSEC-2026-2234

Vulnerability from pysec - Published: 2026-04-08 21:16 - Updated: 2026-07-13 05:50

Details

NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes () in the upload filename. Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows. This vulnerability is fixed in 3.10.0.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Impacted products

Name	purl
nicegui	pkg:pypi/nicegui

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "nicegui",
        "purl": "pkg:pypi/nicegui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
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    }
  ],
  "aliases": [
    "CVE-2026-39844",
    "GHSA-w8wv-vfpc-hw2w"
  ],
  "details": "NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\\) in the upload filename. Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI\u0027s bundled examples) are vulnerable to arbitrary file write on Windows. This vulnerability is fixed in 3.10.0.",
  "id": "PYSEC-2026-2234",
  "modified": "2026-07-13T05:50:15.036912Z",
  "published": "2026-04-08T21:16:59.883Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/zauberzeug/nicegui/releases/tag/v3.10.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-w8wv-vfpc-hw2w"
    },
    {
      "type": "FIX",
      "url": "https://github.com/zauberzeug/nicegui/commit/d38a702e3af2da5b0708f689be8d71413fc77056"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

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How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-39844 (GCVE-0-2026-39844)

FKIE_CVE-2026-39844

GHSA-W8WV-VFPC-HW2W

Summary

Details

Impact

PYSEC-2026-2234

Tags

Sightings

Nomenclature

Vulnerability timeline

Related by attack behaviour