CVE-2023-25577: Werkzeug may allow high resource usage when parsing multipart form data with many fields

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-02-14 · updated 2026-06-17
Weakness: CWE-770

Description

Werkzeug is a comprehensive WSGI web application library. Prior to version 2.2.3, Werkzeug's multipart form data parser will parse an unlimited number of parts, including file parts. Parts can be a small amount of bytes, but each requires CPU time to parse and may use more memory as Python data. If a request can be made to an endpoint that accesses `request.data`, `request.form`, `request.files`, or `request.get_data(parse_form_data=False)`, it can cause unexpectedly high resource usage. This allows an attacker to cause a denial of service by sending crafted multipart data to an endpoint that will parse it. The amount of CPU time required can block worker processes from handling legitimate requests. The amount of RAM required can trigger an out of memory kill of the process. Unlimited file parts can use up memory and file handles. If many concurrent requests are sent continuously, this can exhaust or kill all available workers. Version 2.2.3 contains a patch for this issue.

Affected products

pallets werkzeug: before 2.2.3 — fixed in 2.2.3
Pypi Werkzeug: before 2.2.3; 0.1, 0.10, 0.10.1, 0.10.2, 0.10.3, 0.10.4 (+74) — fixed in 2.2.3

How to fix

Upgrade to a fixed version: pallets werkzeug 2.2.3; Pypi Werkzeug 2.2.3. Check the vendor advisory for mitigations.

References

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