{"id":"CVE-2019-16791","aliases":["GHSA-h92m-42h4-82f6","PYSEC-2020-174"],"title":"postfix-mta-sts-resolver Algorithm Downgrade vulnerability","summary":"postfix-mta-sts-resolver Algorithm Downgrade vulnerability","severity":"medium","cvss":6.9,"cvssVector":"CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N","vendor":"postfix-mta-sts-resolver","product":"postfix-mta-sts-resolver","ecosystem":"pip","affected":["postfix-mta-sts-resolver < 0.5.1"],"patched":["postfix-mta-sts-resolver 0.5.1"],"published":"2019-07-05","updated":"2026-09-10","sourceUpdated":"2026-09-10T03:47:52.688559963Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-h92m-42h4-82f6","references":[{"url":"https://github.com/Snawoot/postfix-mta-sts-resolver/security/advisories/GHSA-h92m-42h4-82f6"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2019-16791"},{"url":"https://gist.github.com/Snawoot/b9da85d6b26dea5460673b29df1adc6b"},{"url":"https://github.com/Snawoot/postfix-mta-sts-resolver"},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/postfix-mta-sts-resolver/PYSEC-2020-174.yaml"}],"tags":["osv","pip"],"epss":0.00784,"epssPercentile":0.54554,"ingestedAt":"2026-09-12T03:13:01.699Z","slug":"CVE-2019-16791","body":"## Overview\n\n## 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)\n\n## Affected packages\n\n- `postfix-mta-sts-resolver < 0.5.1`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `postfix-mta-sts-resolver 0.5.1`","depth":"sunlit","depthScore":38,"depthScoreParts":{"impact":38,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}