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Python-Multipart has Arbitrary File Write via Non-Default Configuration

High severity GitHub Reviewed Published Jan 25, 2026 in Kludex/python-multipart • Updated Jan 26, 2026

Package

pip python-multipart (pip)

Affected versions

< 0.0.22

Patched versions

0.0.22

Description

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.

References

@Kludex Kludex published to Kludex/python-multipart Jan 25, 2026
Published to the GitHub Advisory Database Jan 26, 2026
Reviewed Jan 26, 2026
Last updated Jan 26, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

EPSS score

Weaknesses

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

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

CVE ID

CVE-2026-24486

GHSA ID

GHSA-wp53-j4wj-2cfg

Source code

Credits

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