PYSEC-2026-1852

Vulnerability from pysec - Published: 2026-07-07 16:03 - Updated: 2026-07-07 17:25
VLAI
Details

Summary

A Path Traversal vulnerability exists when using non-default configuration options UPLOAD_DIR and UPLOAD_KEEP_FILENAME=True. An attacker can write uploaded files to arbitrary locations on the filesystem by crafting a malicious filename.

Details

When UPLOAD_DIR is set and UPLOAD_KEEP_FILENAME is True, the library constructs the file path using os.path.join(file_dir, fname). Due to the behavior of os.path.join(), if the filename begins with a /, all preceding path components are discarded:

os.path.join("/upload/dir", "/etc/malicious") == "/etc/malicious"

This allows an attacker to bypass the intended upload directory and write files to arbitrary paths.

Affected Configuration

Projects are only affected if all of the following are true:
- UPLOAD_DIR is set - UPLOAD_KEEP_FILENAME is set to True - The uploaded file exceeds MAX_MEMORY_FILE_SIZE (triggering a flush to disk)

The default configuration is not vulnerable.

Impact

Arbitrary file write to attacker-controlled paths on the filesystem.

Mitigation

Upgrade to version 0.0.22, or avoid using UPLOAD_KEEP_FILENAME=True in project configurations.

Severity
8.6 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
Impacted products
Name purl
python-multipart pkg:pypi/python-multipart
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "python-multipart",
        "purl": "pkg:pypi/python-multipart"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.0.22"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.1",
        "0.0.10",
        "0.0.11",
        "0.0.12",
        "0.0.13",
        "0.0.14",
        "0.0.15",
        "0.0.16",
        "0.0.17",
        "0.0.18",
        "0.0.19",
        "0.0.2",
        "0.0.20",
        "0.0.21",
        "0.0.3",
        "0.0.4",
        "0.0.5",
        "0.0.6",
        "0.0.7",
        "0.0.8",
        "0.0.9"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-24486",
    "GHSA-wp53-j4wj-2cfg"
  ],
  "details": "### Summary\n\nA Path Traversal vulnerability exists when using non-default configuration options `UPLOAD_DIR` and `UPLOAD_KEEP_FILENAME=True`. An attacker can write uploaded files to arbitrary locations on the filesystem by crafting a malicious filename.\n\n### Details\n\nWhen `UPLOAD_DIR` is set and `UPLOAD_KEEP_FILENAME` is `True`, the library constructs the file path using `os.path.join(file_dir, fname)`. Due to the behavior of `os.path.join()`, if the filename begins with a `/`, all preceding path components are discarded:\n\n```py\nos.path.join(\"/upload/dir\", \"/etc/malicious\") == \"/etc/malicious\"\n```\n                        \nThis allows an attacker to bypass the intended upload directory and write files to arbitrary paths.                                         \n                                                                                                                                              \n#### Affected Configuration                                                                                                                      \n                                                                                                                                              \nProjects are only affected if all of the following are true:                                                                                     \n- `UPLOAD_DIR` is set\n- `UPLOAD_KEEP_FILENAME` is set to True\n- The uploaded file exceeds `MAX_MEMORY_FILE_SIZE` (triggering a flush to disk)\n\nThe default configuration is not vulnerable.                                                                                                \n                                                                                                                                              \n#### Impact                                                                                                                                   \n                                                                                                                                              \nArbitrary file write to attacker-controlled paths on the filesystem.                                                                        \n                                                                                                                                              \n#### Mitigation                                                                                                                                  \n                                                                                                                                              \nUpgrade to version 0.0.22, or avoid using `UPLOAD_KEEP_FILENAME=True` in project configurations.",
  "id": "PYSEC-2026-1852",
  "modified": "2026-07-07T17:25:14.687761Z",
  "published": "2026-07-07T16:03:20.509610Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-wp53-j4wj-2cfg"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-24486"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/commit/9433f4bbc9652bdde82bbe380984e32f8cfc89c4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/Kludex/python-multipart"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/releases/tag/0.0.22"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/python-multipart"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-wp53-j4wj-2cfg"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Python-Multipart has Arbitrary File Write via Non-Default Configuration"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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.



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.