CVE-2020-28935 (GCVE-0-2020-28935)
Vulnerability from cvelistv5
Published
2020-12-07 21:46
Modified
2024-09-16 23:27
Severity ?
CWE
  • CWE-59 - Improper Link Resolution Before File Access ('Link Following')
Summary
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.
References
Impacted products
Vendor Product Version
NLnet Labs Unbound Version: <= 1.12.0
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "adp": [
      {
        "providerMetadata": {
          "dateUpdated": "2024-08-04T16:48:00.719Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "tags": [
              "x_transferred"
            ],
            "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"
          },
          {
            "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"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c= 1.12.0"
            }
          ]
        },
        {
          "product": "NSD",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c= 4.3.3"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "value": "We would like to thank Mason Loring Bliss for bringing the issue to our attention."
        }
      ],
      "datePublic": "2020-12-01T00:00:00",
      "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."
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-59",
              "description": "CWE-59: Improper Link Resolution Before File Access (\u0027Link Following\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2023-03-29T00:00:00",
        "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
        "shortName": "NLnet Labs"
      },
      "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"
        }
      ],
      "title": "Local symlink attack in Unbound and NSD"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
    "assignerShortName": "NLnet Labs",
    "cveId": "CVE-2020-28935",
    "datePublished": "2020-12-07T21:46:47.878342Z",
    "dateReserved": "2020-11-18T00:00:00",
    "dateUpdated": "2024-09-16T23:27:01.127Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2020-28935\",\"sourceIdentifier\":\"sep@nlnetlabs.nl\",\"published\":\"2020-12-07T22:15:20.853\",\"lastModified\":\"2024-11-21T05:23:19.620\",\"vulnStatus\":\"Modified\",\"cveTags\":[],\"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.\"},{\"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\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6}],\"cvssMetricV2\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"2.0\",\"vectorString\":\"AV:L/AC:L/Au:N/C:N/I:N/A:P\",\"baseScore\":2.1,\"accessVector\":\"LOCAL\",\"accessComplexity\":\"LOW\",\"authentication\":\"NONE\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"PARTIAL\"},\"baseSeverity\":\"LOW\",\"exploitabilityScore\":3.9,\"impactScore\":2.9,\"acInsufInfo\":false,\"obtainAllPrivilege\":false,\"obtainUserPrivilege\":false,\"obtainOtherPrivilege\":false,\"userInteractionRequired\":false}]},\"weaknesses\":[{\"source\":\"sep@nlnetlabs.nl\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-59\"}]},{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-59\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:nlnetlabs:name_server_daemon:*:*:*:*:*:*:*:*\",\"versionEndExcluding\":\"4.3.4\",\"matchCriteriaId\":\"2999AD3A-4E86-4E7F-94DC-7972AF046056\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*\",\"versionEndExcluding\":\"1.13.0\",\"matchCriteriaId\":\"B5033957-63F8-4F49-A451-96BEF9644520\"}]}]},{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*\",\"matchCriteriaId\":\"DEECE5FC-CACF-4496-A3E7-164736409252\"}]}]}],\"references\":[{\"url\":\"https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html\",\"source\":\"sep@nlnetlabs.nl\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2023/03/msg00024.html\",\"source\":\"sep@nlnetlabs.nl\"},{\"url\":\"https://security.gentoo.org/glsa/202101-38\",\"source\":\"sep@nlnetlabs.nl\",\"tags\":[\"Third Party 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\",\"source\":\"sep@nlnetlabs.nl\",\"tags\":[\"Vendor Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Mailing List\",\"Third Party Advisory\"]},{\"url\":\"https://lists.debian.org/debian-lts-announce/2023/03/msg00024.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"https://security.gentoo.org/glsa/202101-38\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Third Party Advisory\"]},{\"url\":\"https://www.nlnetlabs.nl/downloads/nsd/CVE-2020-28935.txt\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Vendor Advisory\"]},{\"url\":\"https://www.nlnetlabs.nl/downloads/unbound/CVE-2020-28935.txt\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Vendor Advisory\"]}]}}"
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.