id: GO-2023-1569
modules:
    - module: std
      versions:
        - fixed: 1.19.6
        - introduced: 1.20.0-0
          fixed: 1.20.1
      vulnerable_at: 1.20.0
      packages:
        - package: mime/multipart
          symbols:
            - Reader.ReadForm
summary: Excessive resource consumption in mime/multipart
description: |-
    A denial of service is possible from excessive resource consumption in net/http
    and mime/multipart.

    Multipart form parsing with mime/multipart.Reader.ReadForm can consume largely
    unlimited amounts of memory and disk files. This also affects form parsing in
    the net/http package with the Request methods FormFile, FormValue,
    ParseMultipartForm, and PostFormValue.

    ReadForm takes a maxMemory parameter, and is documented as storing "up to
    maxMemory bytes +10MB (reserved for non-file parts) in memory". File parts which
    cannot be stored in memory are stored on disk in temporary files. The
    unconfigurable 10MB reserved for non-file parts is excessively large and can
    potentially open a denial of service vector on its own. However, ReadForm did
    not properly account for all memory consumed by a parsed form, such as map entry
    overhead, part names, and MIME headers, permitting a maliciously crafted form to
    consume well over 10MB. In addition, ReadForm contained no limit on the number
    of disk files created, permitting a relatively small request body to create a
    large number of disk temporary files.

    With fix, ReadForm now properly accounts for various forms of memory overhead,
    and should now stay within its documented limit of 10MB + maxMemory bytes of
    memory consumption. Users should still be aware that this limit is high and may
    still be hazardous.

    In addition, ReadForm now creates at most one on-disk temporary file, combining
    multiple form parts into a single temporary file. The mime/multipart.File
    interface type's documentation states, "If stored on disk, the File's underlying
    concrete type will be an *os.File.". This is no longer the case when a form
    contains more than one file part, due to this coalescing of parts into a single
    file. The previous behavior of using distinct files for each form part may be
    reenabled with the environment variable GODEBUG=multipartfiles=distinct.

    Users should be aware that multipart.ReadForm and the http.Request methods that
    call it do not limit the amount of disk consumed by temporary files. Callers can
    limit the size of form data with http.MaxBytesReader.
credits:
    - Arpad Ryszka
    - Jakob Ackermann (@das7pad)
references:
    - report: https://go.dev/issue/58006
    - fix: https://go.dev/cl/468124
    - web: https://groups.google.com/g/golang-announce/c/V0aBFqaFs_E
cve_metadata:
    id: CVE-2022-41725
    cwe: 'CWE-400: Uncontrolled Resource Consumption'
    references:
        - https://security.gentoo.org/glsa/202311-09