{"id":"UBUNTU-CVE-2026-53537","details":"Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, parse_options_header parsed Content-Disposition (and Content-Type) headers with email.message.Message, which transparently applies RFC 2231/5987 decoding. The extended parameter syntax (filename*=charset'lang'value, name*=..., and the filename*0/filename*1 continuation form) is decoded and surfaced under the bare filename/name key, and overrides the plain parameter when both are present. RFC 7578 §4.2 explicitly forbids the filename* form in multipart/form-data. Components that follow RFC 7578, or that do not implement RFC 2231/5987 decoding for multipart/form-data (WAFs, proxies, gateways), may interpret such a header differently. An attacker can exploit that difference to smuggle a different field name or filename past an upstream inspector to the backend. This vulnerability is fixed in 0.0.30.","modified":"2026-06-29T13:55:02.244498995Z","published":"2026-06-22T18:16:00Z","upstream":["CVE-2026-53537"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-53537"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-53537"}],"affected":[{"package":{"name":"python-multipart","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/python-multipart?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.0.5-2","0.0.5-2ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"0.0.5-2ubuntu0.1~esm1","binary_name":"python3-multipart"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-53537.json"}},{"package":{"name":"python-multipart","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/python-multipart?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.0.5-3","0.0.6-1","0.0.9-1","0.0.9-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-multipart","binary_version":"0.0.9-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-53537.json"}},{"package":{"name":"python-multipart","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/python-multipart?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.0.20-1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-python-multipart","binary_version":"0.0.20-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-53537.json"}},{"package":{"name":"python-multipart","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/python-multipart?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.0.20-1","0.0.20-1.1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-python-multipart","binary_version":"0.0.20-1.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-53537.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},{"type":"Ubuntu","score":"medium"}]}