{"dataType": "CVE_RECORD", "dataVersion": "5.1", "cveMetadata": {"state": "PUBLISHED", "cveId": "CVE-2020-28935", "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6", "assignerShortName": "NLnet Labs", "dateUpdated": "2024-09-16T23:27:01.127Z", "dateReserved": "2020-11-18T00:00:00", "datePublished": "2020-12-07T21:46:47.878342Z"}, "containers": {"cna": {"title": "Local symlink attack in Unbound and NSD", "datePublic": "2020-12-01T00:00:00", "providerMetadata": {"orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6", "shortName": "NLnet Labs", "dateUpdated": "2023-03-29T00:00:00"}, "descriptions": [{"lang": "en", "value": "NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system."}], "affected": [{"vendor": "NLnet Labs", "product": "Unbound", "versions": [{"version": "<= 1.12.0", "status": "affected"}]}, {"vendor": "NLnet Labs", "product": "NSD", "versions": [{"version": "<= 4.3.3", "status": "affected"}]}], "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2020-28935.txt"}, {"url": "https://www.nlnetlabs.nl/downloads/nsd/CVE-2020-28935.txt"}, {"name": "GLSA-202101-38", "tags": ["vendor-advisory"], "url": "https://security.gentoo.org/glsa/202101-38"}, {"name": "[debian-lts-announce] 20210212 [SECURITY] [DLA 2556-1] unbound1.9 security update", "tags": ["mailing-list"], "url": "https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html"}, {"name": "[debian-lts-announce] 20230329 [SECURITY] [DLA 3371-1] unbound security update", "tags": ["mailing-list"], "url": "https://lists.debian.org/debian-lts-announce/2023/03/msg00024.html"}], "credits": [{"lang": "en", "value": "We would like to thank Mason Loring Bliss for bringing the issue to our attention."}], "problemTypes": [{"descriptions": [{"type": "CWE", "lang": "en", "description": "CWE-59: Improper Link Resolution Before File Access ('Link Following')", "cweId": "CWE-59"}]}]}, "adp": [{"providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T16:48:00.719Z"}, "title": "CVE Program Container", "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2020-28935.txt", "tags": ["x_transferred"]}, {"url": "https://www.nlnetlabs.nl/downloads/nsd/CVE-2020-28935.txt", "tags": ["x_transferred"]}, {"name": "GLSA-202101-38", "tags": ["vendor-advisory", "x_transferred"], "url": "https://security.gentoo.org/glsa/202101-38"}, {"name": "[debian-lts-announce] 20210212 [SECURITY] [DLA 2556-1] unbound1.9 security update", "tags": ["mailing-list", "x_transferred"], "url": "https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html"}, {"name": "[debian-lts-announce] 20230329 [SECURITY] [DLA 3371-1] unbound security update", "tags": ["mailing-list", "x_transferred"], "url": "https://lists.debian.org/debian-lts-announce/2023/03/msg00024.html"}]}]}}

{}

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When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system."}, {"lang": "es", "value": "NLnet Labs Unbound, hasta la versi\u00f3n 1.12.0 incluy\u00e9ndola, y NLnet Labs NSD, hasta la versi\u00f3n 4.3.3 incluy\u00e9ndola, contienen una vulnerabilidad local que permitir\u00eda un ataque de tipo symlink local. Al escribir el archivo PID, Unbound y NSD crean el archivo si no est\u00e1 all\u00ed, o abren un archivo existente para escribir. En caso de que el archivo ya existiera, seguir\u00edan enlaces simb\u00f3licos si el archivo fuera un enlace simb\u00f3lico en lugar de un archivo normal. Luego, se llevar\u00eda a cabo una copia adicional del archivo despu\u00e9s de que se escribi\u00f3, lo que har\u00eda que el usuario Unbound/NSD se ejecute como el nuevo propietario del archivo. Si un atacante tiene acceso local al usuario con el que se ejecuta Unbound/NSD, podr\u00eda crear un enlace simb\u00f3lico en lugar del archivo PID que apunta hacia un archivo que le gustar\u00eda borrar. Si luego Unbound/NSD es eliminado y el archivo PID no se borra, al reiniciar con privilegios root, Unbound/NSD reescribir\u00e1 cualquier archivo apuntado por el enlace simb\u00f3lico. Esta es una vulnerabilidad local que podr\u00eda crear una Denegaci\u00f3n de Servicio del sistema en el que se ejecuta Unbound/NSD. Requiere que un atacante tenga acceso al usuario de permiso limitado que se ejecuta como Unbound/NSD y apunta por medio del enlace simb\u00f3lico a un archivo cr\u00edtico en el sistema"}], "id": "CVE-2020-28935", "lastModified": "2023-03-29T15:15:07.057", "metrics": {"cvssMetricV2": [{"acInsufInfo": false, "baseSeverity": "LOW", "cvssData": {"accessComplexity": "LOW", "accessVector": "LOCAL", "authentication": "NONE", "availabilityImpact": "PARTIAL", "baseScore": 2.1, "confidentialityImpact": "NONE", "integrityImpact": "NONE", "vectorString": "AV:L/AC:L/Au:N/C:N/I:N/A:P", "version": "2.0"}, "exploitabilityScore": 3.9, "impactScore": 2.9, "obtainAllPrivilege": false, "obtainOtherPrivilege": false, "obtainUserPrivilege": false, "source": "nvd@nist.gov", "type": "Primary", "userInteractionRequired": false}], "cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 5.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 3.6, "source": "nvd@nist.gov", "type": "Primary"}]}, "published": "2020-12-07T22:15:20.853", "references": [{"source": "sep@nlnetlabs.nl", "tags": ["Mailing List", "Third Party Advisory"], "url": "https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html"}, {"source": "sep@nlnetlabs.nl", "url": "https://lists.debian.org/debian-lts-announce/2023/03/msg00024.html"}, {"source": "sep@nlnetlabs.nl", "tags": ["Third Party Advisory"], "url": "https://security.gentoo.org/glsa/202101-38"}, {"source": "sep@nlnetlabs.nl", "tags": ["Vendor Advisory"], "url": "https://www.nlnetlabs.nl/downloads/nsd/CVE-2020-28935.txt"}, {"source": "sep@nlnetlabs.nl", "tags": ["Vendor Advisory"], "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2020-28935.txt"}], "sourceIdentifier": "sep@nlnetlabs.nl", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-59"}], "source": "nvd@nist.gov", "type": "Primary"}, {"description": [{"lang": "en", "value": "CWE-59"}], "source": "sep@nlnetlabs.nl", "type": "Secondary"}]}

{"acknowledgement": "This issue was discovered by Mason Loring Bliss (Red Hat).", "affected_release": [{"advisory": "RHSA-2021:1853", "cpe": "cpe:/a:redhat:enterprise_linux:8", "package": "unbound-0:1.7.3-15.el8", "product_name": "Red Hat Enterprise Linux 8", "release_date": "2021-05-18T00:00:00Z"}, {"advisory": "RHSA-2022:0632", "cpe": "cpe:/a:redhat:rhel_eus:8.2", "package": "unbound-0:1.7.3-12.el8_2", "product_name": "Red Hat Enterprise Linux 8.2 Extended Update Support", "release_date": "2022-02-22T00:00:00Z"}], "bugzilla": {"description": "unbound: symbolic link traversal when writing PID file", "id": "1878761", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=1878761"}, "csaw": false, "cvss3": {"cvss3_base_score": "4.4", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N", "status": "verified"}, "cwe": "CWE-59", "details": ["NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system.", "A symbolic link traversal vulnerability was found in unbound in the way it writes its PID file while starting up. This flaw allows a local attacker with access to the unbound user to set up a link to another file, owned by root, and make unbound overwrite it during its next restart, destroying the original content. The highest threat from this vulnerability is integrity."], "mitigation": {"lang": "en:us", "value": "If SELinux is enabled in Enforcing mode (the default value in Red Hat Enterprise Linux 8), this kind of attack is prevented as unbound would be blocked from accessing the symbolic link file."}, "name": "CVE-2020-28935", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2020-09-09T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2020-28935\nhttps://nvd.nist.gov/vuln/detail/CVE-2020-28935"], "threat_severity": "Low", "upstream_fix": "unbound 1.13.0"}