{"id":"UBUNTU-CVE-2026-53539","details":"Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.","modified":"2026-06-24T11:01:50.834609632Z","published":"2026-06-22T18:16:00Z","upstream":["CVE-2026-53539"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-53539"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-53539"}],"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-2026-53539.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-2026-53539.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-2026-53539.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-2026-53539.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"Ubuntu","score":"medium"}]}