{"schemaVersion":3,"id":"CVE-2021-3634","aliases":["MGASA-2021-0441","RHSA-2022:2031","UBUNTU-CVE-2021-3634","USN-5053-1","DEBIAN-CVE-2021-3634","DSA-4965-1"],"status":"published","duplicateOf":null,"title":null,"description":"A flaw has been found in libssh in versions prior to 0.9.6. The SSH protocol keeps track of two shared secrets during the lifetime of the session. One of them is called secret_hash and the other session_id. Initially, both of them are the same, but after key re-exchange, previous session_id is kept and used as an input to new secret_hash. Historically, both of these buffers had shared length variable, which worked as long as these buffers were same. But the key re-exchange operation can also change the key exchange method, which can be based on hash of different size, eventually creating \"secret_hash\" of different size than the session_id has. This becomes an issue when the session_id memory is zeroed or when it is used again during second key re-exchange.","dates":{"published":"2021-08-31T00:00:00.000Z","modified":"2024-08-03T17:01:07.562Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":6.5,"severity":"medium","version":"3.1","versionLabel":"v3.1","source":"NVD","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"OSV · Red hat","score":3.5,"severity":"low","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L","exploitability":5.4,"impact":2.3,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Ubuntu","score":6.5,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","exploitability":7.2,"impact":6,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Debian","score":6.5,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","exploitability":7.2,"impact":6,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":6.5,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","exploitability":null,"impact":null,"computed":false},{"version":"2.0","versionLabel":"v2.0","source":"NVD","score":4,"severity":"medium","vector":"AV:N/AC:L/Au:S/C:N/I:N/A:P","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.04683,"percentile":0.91669,"severity":"low","asOf":"2026-10-18T00:00:00.000Z","change":{"pp":0,"baselineDate":"2026-09-18T00:00:00.000Z","baselineScore":0.04683},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.04683,"percentile":0.91669}],"last30":[{"date":"2026-09-18T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.04683,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.04683,"percentile":0.91669}]},"kev":{"state":"not-listed","entries":[],"listedCount":0,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":false,"entry":null},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"none-recorded","sources":[]},"exploits":[],"exploitCount":0,"weaknesses":[{"id":"CWE-787","name":"Out-of-bounds Write","description":"The product writes data past the end, or before the beginning, of the intended buffer.","type":"weakness","status":"Draft","abstraction":"Base","likelihoodOfExploit":"High","url":"https://cwe.mitre.org/data/definitions/787.html"}],"affected":[{"vendor":"debian","product":"libssh","name":"libssh","label":"libssh","ecosystem":"Debian","cpePart":null,"purl":"pkg:deb/debian/libssh","purlType":"deb","versions":[{"text":"< 0.9.6-1","noFixRecorded":false,"fixedIn":null},{"text":"< 0.9.5-1+deb11u1","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0.9.6-1 | < 0.9.5-1+deb11u1","eol":null,"hubHref":null},{"vendor":"ubuntu","product":"libssh","name":"libssh","label":"libssh","ecosystem":"Ubuntu","cpePart":null,"purl":"pkg:deb/ubuntu/libssh","purlType":"deb","versions":[{"text":"< 0.9.3-2ubuntu2.2","noFixRecorded":false,"fixedIn":null},{"text":"< 0.9.6-1","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0.9.3-2ubuntu2.2 | < 0.9.6-1","eol":null,"hubHref":null},{"vendor":"debian","product":"debian_linux","name":"debian linux","label":"debian_linux","ecosystem":null,"cpePart":"o","purl":null,"purlType":null,"versions":[{"text":"10.0","noFixRecorded":false,"fixedIn":null},{"text":"11.0","noFixRecorded":false,"fixedIn":null}],"versionsText":"10.0 | 11.0","eol":{"isEol":true,"eolDate":"2024-06-30T00:00:00.000Z","matchMethod":"cpe","cycle":{"name":"10","label":"10 (Buster)","eolFrom":"2024-06-30T00:00:00.000Z","isLts":false,"isMaintained":true,"latestVersion":"10.13"},"product":{"name":"debian","label":"Debian","category":"os"}},"hubHref":"/vendor/debian/debian_linux"},{"vendor":"fedoraproject","product":"fedora","name":"fedora","label":"fedora","ecosystem":null,"cpePart":"o","purl":null,"purlType":null,"versions":[{"text":"33","noFixRecorded":false,"fixedIn":null},{"text":"34","noFixRecorded":false,"fixedIn":null},{"text":"35","noFixRecorded":false,"fixedIn":null}],"versionsText":"33 | 34 | 35","eol":{"isEol":true,"eolDate":"2021-11-30T00:00:00.000Z","matchMethod":"cpe","cycle":{"name":"33","label":"33","eolFrom":"2021-11-30T00:00:00.000Z","isLts":false,"isMaintained":false,"latestVersion":null},"product":{"name":"fedora","label":"Fedora Linux","category":"os"}},"hubHref":"/vendor/fedoraproject/fedora"},{"vendor":"libssh","product":"libssh","name":"libssh","label":"libssh","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≥ 0.9.1, < 0.9.6","noFixRecorded":false,"fixedIn":null}],"versionsText":"≥ 0.9.1, < 0.9.6","eol":null,"hubHref":"/vendor/libssh/libssh"},{"vendor":"mageia","product":"libssh","name":"libssh","label":"libssh","ecosystem":"Mageia","cpePart":null,"purl":"pkg:rpm/mageia/libssh","purlType":"rpm","versions":[{"text":"< 0.9.6-1.mga8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0.9.6-1.mga8","eol":null,"hubHref":null},{"vendor":"netapp","product":"cloud_backup","name":"cloud backup","label":"cloud_backup","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"na","noFixRecorded":false,"fixedIn":null}],"versionsText":"na","eol":null,"hubHref":"/vendor/netapp/cloud_backup"},{"vendor":"oracle","product":"mysql_workbench","name":"mysql workbench","label":"mysql_workbench","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"≤ 8.0.27","noFixRecorded":false,"fixedIn":null}],"versionsText":"≤ 8.0.27","eol":null,"hubHref":"/vendor/oracle/mysql_workbench"},{"vendor":"redhat","product":"enterprise_linux","name":"enterprise linux","label":"enterprise_linux","ecosystem":null,"cpePart":"o","purl":null,"purlType":null,"versions":[{"text":"8.0","noFixRecorded":false,"fixedIn":null}],"versionsText":"8.0","eol":{"isEol":false,"eolDate":"2029-05-31T00:00:00.000Z","matchMethod":"cpe","cycle":{"name":"8","label":"8 (Upcoming ELS)","eolFrom":"2029-05-31T00:00:00.000Z","isLts":false,"isMaintained":true,"latestVersion":"8.10"},"product":{"name":"rhel","label":"Red Hat Enterprise Linux","category":"os"}},"hubHref":"/vendor/redhat/enterprise_linux"},{"vendor":"redhat","product":"virtualization","name":"virtualization","label":"virtualization","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"4.0","noFixRecorded":false,"fixedIn":null}],"versionsText":"4.0","eol":null,"hubHref":"/vendor/redhat/virtualization"},{"vendor":"redhat","product":"libssh","name":"libssh","label":"libssh","ecosystem":"Red Hat","cpePart":null,"purl":"pkg:rpm/redhat/libssh","purlType":"rpm","versions":[{"text":"< 0:0.9.6-3.el8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0:0.9.6-3.el8","eol":null,"hubHref":null},{"vendor":"redhat","product":"libssh-config","name":"libssh-config","label":"libssh-config","ecosystem":"Red Hat","cpePart":null,"purl":"pkg:rpm/redhat/libssh-config","purlType":"rpm","versions":[{"text":"< 0:0.9.6-3.el8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0:0.9.6-3.el8","eol":null,"hubHref":null},{"vendor":"redhat","product":"libssh-debuginfo","name":"libssh-debuginfo","label":"libssh-debuginfo","ecosystem":"Red Hat","cpePart":null,"purl":"pkg:rpm/redhat/libssh-debuginfo","purlType":"rpm","versions":[{"text":"< 0:0.9.6-3.el8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0:0.9.6-3.el8","eol":null,"hubHref":null},{"vendor":"redhat","product":"libssh-debugsource","name":"libssh-debugsource","label":"libssh-debugsource","ecosystem":"Red Hat","cpePart":null,"purl":"pkg:rpm/redhat/libssh-debugsource","purlType":"rpm","versions":[{"text":"< 0:0.9.6-3.el8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0:0.9.6-3.el8","eol":null,"hubHref":null},{"vendor":"redhat","product":"libssh-devel","name":"libssh-devel","label":"libssh-devel","ecosystem":"Red Hat","cpePart":null,"purl":"pkg:rpm/redhat/libssh-devel","purlType":"rpm","versions":[{"text":"< 0:0.9.6-3.el8","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 0:0.9.6-3.el8","eol":null,"hubHref":null}],"affectedCount":15,"eol":{"hasEol":true,"count":2},"references":[{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1978810","label":"bugzilla.redhat.com/show_bug.cgi?id=1978810","hostname":"bugzilla.redhat.com","tags":["REPORT","Issue Tracking","Third Party Advisory"]},{"url":"https://www.debian.org/security/2021/dsa-4965","label":"www.debian.org/security/2021/dsa-4965","hostname":"www.debian.org","tags":["Vendor Advisory","WEB","Third Party Advisory"]},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/","label":"lists.fedoraproject.org/archives/…","hostname":"lists.fedoraproject.org","tags":["Vendor Advisory"]},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/","label":"lists.fedoraproject.org/archives/…","hostname":"lists.fedoraproject.org","tags":["Vendor Advisory"]},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/","label":"lists.fedoraproject.org/archives/…","hostname":"lists.fedoraproject.org","tags":["Vendor Advisory"]},{"url":"https://www.oracle.com/security-alerts/cpujan2022.html","label":"www.oracle.com/security-alerts/cpujan2022.html","hostname":"www.oracle.com","tags":["Patch","Third Party Advisory"]},{"url":"https://security.netapp.com/advisory/ntap-20211004-0003/","label":"security.netapp.com/advisory/ntap-20211004-0003/","hostname":"security.netapp.com","tags":["Third Party Advisory"]},{"url":"https://security.gentoo.org/glsa/202312-05","label":"security.gentoo.org/glsa/202312-05","hostname":"security.gentoo.org","tags":["Vendor Advisory"]},{"url":"https://advisories.mageia.org/MGASA-2021-0441.html","label":"advisories.mageia.org/MGASA-2021-0441.html","hostname":"advisories.mageia.org","tags":["Advisory"]},{"url":"https://bugs.mageia.org/show_bug.cgi?id=29419","label":"bugs.mageia.org/show_bug.cgi?id=29419","hostname":"bugs.mageia.org","tags":["REPORT"]},{"url":"https://www.libssh.org/security/advisories/CVE-2021-3634.txt","label":"www.libssh.org/security/advisories/CVE-2021-3634.txt","hostname":"www.libssh.org","tags":["Advisory"]},{"url":"https://www.libssh.org/2021/08/26/libssh-0-9-6-security-release/","label":"www.libssh.org/2021/08/26/libssh-0-9-6-security-release/","hostname":"www.libssh.org","tags":["WEB"]},{"url":"https://ubuntu.com/security/notices/USN-5053-1","label":"ubuntu.com/security/notices/USN-5053-1","hostname":"ubuntu.com","tags":["Advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2022:2031","label":"access.redhat.com/errata/RHSA-2022:2031","hostname":"access.redhat.com","tags":["Advisory"]},{"url":"https://access.redhat.com/security/updates/classification/#low","label":"access.redhat.com/security/updates/classification/","hostname":"access.redhat.com","tags":["ARTICLE"]},{"url":"https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/8.6_release_notes/","label":"access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/8.6_release_notes/","hostname":"access.redhat.com","tags":["ARTICLE"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1896651","label":"bugzilla.redhat.com/show_bug.cgi?id=1896651","hostname":"bugzilla.redhat.com","tags":["REPORT"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2020159","label":"bugzilla.redhat.com/show_bug.cgi?id=2020159","hostname":"bugzilla.redhat.com","tags":["REPORT"]},{"url":"https://security.access.redhat.com/data/csaf/v2/advisories/2022/rhsa-2022_2031.json","label":"security.access.redhat.com/data/csaf/v2/advisories/2022/rhsa-2022_2031.json","hostname":"security.access.redhat.com","tags":["Advisory"]},{"url":"https://access.redhat.com/security/cve/CVE-2021-3634","label":"access.redhat.com/security/cve/CVE-2021-3634","hostname":"access.redhat.com","tags":["REPORT"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-3634","label":"www.cve.org/CVERecord?id=CVE-2021-3634","hostname":"www.cve.org","tags":["Advisory","REPORT"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-3634","label":"nvd.nist.gov/vuln/detail/CVE-2021-3634","hostname":"nvd.nist.gov","tags":["Advisory","Oval"]},{"url":"https://ubuntu.com/security/CVE-2021-3634","label":"ubuntu.com/security/CVE-2021-3634","hostname":"ubuntu.com","tags":["REPORT"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2021-3634","label":"security-tracker.debian.org/tracker/CVE-2021-3634","hostname":"security-tracker.debian.org","tags":["Advisory"]}],"lineage":{"upstream":[],"downstream":["OPENSUSE-SU-2024:10998-1","SUSE-SU-2024:0525-1","SUSE-SU-2024:0539-1"],"duplicates":[],"related":["OPENSUSE-SU-2024:10998-1","SUSE-SU-2024:0525-1","SUSE-SU-2024:0539-1"]},"timeline":[{"kind":"published","date":"2021-08-31T00:00:00.000Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2024-08-03T17:01:07.562Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":27,"level":"medium","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-19T06:23:30.457Z","stale":false,"partial":false}}