{"id":"CVE-2019-16791","aliases":["EUVD-2020-0149","GHSA-h92m-42h4-82f6","PYSEC-2020-174","UBUNTU-CVE-2019-16791"],"status":"published","title":"downgrade of effective Strict Transport Security (STS) policy in postfix-mta-sts-resolver","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","severity":{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00858,"percentile":0.58757,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-757"],"published":"2019-07-05T21:06:58Z","modified":"2026-10-20T10:51:37Z","fixes":[{"ecosystem":"PyPI","package":"postfix-mta-sts-resolver","fixed_in":["0.5.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.5.1"}]}]},{"source":"osv","ecosystem":"PyPI","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.5.1"}]}],"versions":["0.1.1","0.1.2","0.1.3","0.1.4","0.1.5","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","0.2.5","0.2.7","0.2.8","0.2.9","0.3.0","0.4.0","0.4.1","0.4.2","0.4.3","0.4.4","0.4.5","0.5.0"]},{"source":"osv","ecosystem":"PyPI","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.5.1"}]}],"versions":["0.1.1","0.1.2","0.1.3","0.1.4","0.1.5","0.2.0","0.2.1","0.2.2","0.2.3","0.2.4","0.2.5","0.2.7","0.2.8","0.2.9","0.3.0","0.4.0","0.4.1","0.4.2","0.4.3","0.4.4","0.4.5","0.5.0"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.6.0-1","0.7.0-1","0.7.3-1","0.7.5-1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.0.0-4","1.1.2-1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.1.2-1.1","1.1.2-1.1ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.0-1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.0-1build1","1.5.1-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"postfix-mta-sts-resolver","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.0-1","1.5.0-1build1"]}],"products":[{"vendor":"postfix-mta-sts-resolver_project","product":"postfix-mta-sts-resolver"},{"vendor":"snawoot","product":"postfix-mta-sts-resolver"}],"references":[{"url":"https://github.com/Snawoot/postfix-mta-sts-resolver/security/advisories/GHSA-h92m-42h4-82f6","tags":["x_refsource_CONFIRM","x_transferred","Patch","Third Party Advisory","fix","web","advisory","report"]},{"url":"https://gist.github.com/Snawoot/b9da85d6b26dea5460673b29df1adc6b","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2019-16791","tags":["advisory"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/postfix-mta-sts-resolver/PYSEC-2020-174.yaml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-h92m-42h4-82f6"},{"url":"https://github.com/Snawoot/postfix-mta-sts-resolver","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2019-16791","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2019-16791","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2019-16791","title":"downgrade of effective Strict Transport Security (STS) policy in postfix-mta-sts-resolver","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T01:40:14Z","modified":"2024-08-05T01:24:47.238Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-757"],"updated_at":"2026-11-02T14:32:23.189113Z"}],"euvd":[{"id":"EUVD-2020-0149","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T01:40:14Z","modified":"2024-08-05T01:24:47Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium"}],"updated_at":"2026-11-03T02:40:31.903592Z"}],"ghsa":[{"id":"GHSA-h92m-42h4-82f6","title":"postfix-mta-sts-resolver Algorithm Downgrade vulnerability","description":"## Incorrect query parsing\n\n### Impact\nAll users of versions prior to 0.5.1 can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.\n\n### Patches\nProblem has been patched in version 0.5.1\n\n### Workarounds\nUsers may remediate this vulnerability without upgrading by applying [these patches](https://gist.github.com/Snawoot/b9da85d6b26dea5460673b29df1adc6b) to older suppoorted versions.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [postfix-mta-sts-resolver repo](https://github.com/Snawoot/postfix-mta-sts-resolver)\n* Email me at [vladislav at vm-0 dot com](mailto:vladislav-ex-gh-advisory@vm-0.com)","status":"published","published":"2019-07-05T21:06:58Z","modified":"2024-10-21T20:07:59Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N","level":"high"},{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium"}],"cwes":["CWE-757"],"updated_at":"2026-11-02T14:38:12.325695Z"}],"nvd":[{"id":"CVE-2019-16791","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T02:15:11.367Z","modified":"2026-06-17T02:22:48.73Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":5.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"medium","assessor":"primary"},{"version":"2.0","score":4.3,"vector":"AV:N/AC:M/Au:N/C:N/I:N/A:P","level":"medium","assessor":"primary"}],"cwes":["CWE-757"],"updated_at":"2026-11-02T14:05:42.416368Z"}],"osv":[{"id":"CVE-2019-16791","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T02:15:11.367Z","modified":"2026-10-20T10:51:37.997798771Z","cvss":[{"version":"3.1","score":5.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-02T15:44:11.673963Z"},{"id":"GHSA-h92m-42h4-82f6","title":"postfix-mta-sts-resolver Algorithm Downgrade vulnerability","description":"## Incorrect query parsing\n\n### Impact\nAll users of versions prior to 0.5.1 can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.\n\n### Patches\nProblem has been patched in version 0.5.1\n\n### Workarounds\nUsers may remediate this vulnerability without upgrading by applying [these patches](https://gist.github.com/Snawoot/b9da85d6b26dea5460673b29df1adc6b) to older suppoorted versions.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [postfix-mta-sts-resolver repo](https://github.com/Snawoot/postfix-mta-sts-resolver)\n* Email me at [vladislav at vm-0 dot com](mailto:vladislav-ex-gh-advisory@vm-0.com)","status":"published","published":"2019-07-05T21:06:58Z","modified":"2026-09-10T03:47:52.688559963Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium"},{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N","level":"high"}],"cwes":["CWE-757"],"updated_at":"2026-11-02T15:46:48.920784Z"},{"id":"UBUNTU-CVE-2019-16791","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T02:15:00Z","modified":"2026-10-17T12:55:41.850393702Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","level":"medium"},{"version":"3.1","score":5.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-02T15:54:20.325378Z"},{"id":"PYSEC-2020-174","description":"In postfix-mta-sts-resolver before 0.5.1, All users can receive incorrect response from daemon under rare conditions, rendering downgrade of effective STS policy.","status":"published","published":"2020-01-22T02:15:00Z","modified":"2023-11-08T04:01:21.829017Z","updated_at":"2026-11-02T15:52:52.192131Z"}]}}