{ "document": { "aggregate_severity": { "text": "Medium" }, "category": "csaf_vex", "csaf_version": "2.0", "distribution": { "text": "TuxCare License Agreement", "tlp": { "label": "WHITE", "url": "https://www.first.org/tlp/" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Cloud Linux Inc. and provide a link to the original.", "title": "Terms of Use" } ], "publisher": { "category": "vendor", "contact_details": "https://tuxcare.com/contact/", "name": "TuxCare", "namespace": "https://tuxcare.com/" }, "references": [ { "category": "self", "summary": "Canonical URL", "url": "https://security.tuxcare.com/csaf/v2/els_os/centos-stream8els/vex/2021/cve-2021-3634-els_os-centos-stream8els.json" } ], "tracking": { "current_release_date": "2026-04-20T15:43:20Z", "generator": { "date": "2026-04-20T15:43:20Z", "engine": { "name": "pyCSAF" } }, "id": "CVE-2021-3634-ELS_OS-CENTOS-STREAM8ELS", "initial_release_date": "2021-08-31T17:15:00Z", "revision_history": [ { "date": "2021-08-31T17:15:00Z", "number": "1", "summary": "Initial version" }, { "date": "2026-04-13T12:34:38Z", "number": "2", "summary": "Official Publication" }, { "date": "2026-04-20T15:43:20Z", "number": "3", 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"product_reference": "libssh-devel-0:0.9.6-14.el8.i686", "relates_to_product_reference": "CentOS-Stream-8" }, { "category": "default_component_of", "full_product_name": { "name": "libssh-config-0:0.9.6-14.el8.noarch as a component of Community Enterprise Operating System 8", "product_id": "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.noarch" }, "product_reference": "libssh-config-0:0.9.6-14.el8.noarch", "relates_to_product_reference": "CentOS-Stream-8" }, { "category": "default_component_of", "full_product_name": { "name": "libssh-0:0.9.6-14.el8.x86_64 as a component of Community Enterprise Operating System 8", "product_id": "CentOS-Stream-8:libssh-0:0.9.6-14.el8.x86_64" }, "product_reference": "libssh-0:0.9.6-14.el8.x86_64", "relates_to_product_reference": "CentOS-Stream-8" }, { "category": "default_component_of", "full_product_name": { "name": "libssh-0:0.9.6-14.el8.i686 as a component of Community Enterprise Operating System 8", "product_id": "CentOS-Stream-8:libssh-0:0.9.6-14.el8.i686" }, "product_reference": "libssh-0:0.9.6-14.el8.i686", "relates_to_product_reference": "CentOS-Stream-8" } ] }, "vulnerabilities": [ { "cve": "CVE-2021-3634", "cwe": { "id": "CWE-787", "name": "Out-of-bounds Write" }, "notes": [ { "category": "description", "text": "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.", "title": "Vulnerability description" }, { "category": "general", "text": "The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.", "title": "CVSS score applicability" } ], "product_status": { "known_affected": [ "CentOS-Stream-8:libssh-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.x86_64", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els1.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els2.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els3.noarch", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.x86_64" ] }, "references": [ { "category": "self", "summary": "Canonical URL", "url": "https://cve.tuxcare.com/els/cve/CVE-2021-3634" }, { "category": "external", "summary": "https://bugzilla.redhat.com/show_bug.cgi?id=1978810", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=1978810" }, { "category": "external", "summary": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/" }, { "category": "external", "summary": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/" }, { "category": "external", "summary": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/" }, { "category": "external", "summary": "https://security.gentoo.org/glsa/202312-05", "url": "https://security.gentoo.org/glsa/202312-05" }, { "category": "external", "summary": "https://security.netapp.com/advisory/ntap-20211004-0003/", "url": "https://security.netapp.com/advisory/ntap-20211004-0003/" }, { "category": "external", "summary": "https://www.debian.org/security/2021/dsa-4965", "url": "https://www.debian.org/security/2021/dsa-4965" }, { "category": "external", "summary": "https://www.oracle.com/security-alerts/cpujan2022.html", "url": "https://www.oracle.com/security-alerts/cpujan2022.html" } ], "release_date": "2021-08-31T17:15:00Z", "remediations": [ { "category": "no_fix_planned", "details": "CVE-2021-3634 only affects libssh 0.9.1–0.9.5 and is exploitable during SSH rekeying when a peer switches to a key‑exchange with a different hash size, leading primarily to out‑of‑bounds access and potential process crash without confidentiality or integrity impact. OpenSSH’s sshd is a different codebase and not affected; unless a workload explicitly exposes a libssh‑based SSH service, the library is typically present only in client‑side components—so exploitation would require those clients to connect to an attacker‑controlled SSH server that forces a rekey. With no publicly demonstrated unauthenticated RCE and a practical outcome limited to denial‑of‑service of the specific libssh‑using process, this issue can be safely deprioritized.", "product_ids": [ "CentOS-Stream-8:libssh-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.x86_64", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els1.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els2.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els3.noarch", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.x86_64" ] } ], "scores": [ { "cvss_v2": { "accessComplexity": "LOW", "accessVector": "NETWORK", "authentication": "SINGLE", "availabilityImpact": "PARTIAL", "baseScore": 4.0, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "vectorString": "AV:N/AC:L/Au:S/C:N/I:N/A:P", "version": "2.0" }, "cvss_v3": { "attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "version": "3.1" }, "products": [ "CentOS-Stream-8:libssh-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-0:0.9.6-14.el8.x86_64", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els1.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els2.noarch", "CentOS-Stream-8:libssh-config-0:0.9.6-14.el8.tuxcare.els3.noarch", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els1.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els2.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.i686", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.tuxcare.els3.x86_64", "CentOS-Stream-8:libssh-devel-0:0.9.6-14.el8.x86_64" ] } ], "threats": [ { "category": "impact", "details": "Moderate" } ] } ] }