Libssh: buffer underflow in ssh_get_hexa() on invalid input

{
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "cveMetadata": {
    "cveId": "CVE-2026-0966",
    "assignerOrgId": "53f830b8-0a3f-465b-8143-3b8a9948e749",
    "assignerShortName": "redhat",
    "dateUpdated": "2026-03-26T20:06:28.313Z",
    "dateReserved": "2026-01-14T21:54:59.132Z",
    "datePublished": "2026-03-26T20:06:28.313Z",
    "state": "PUBLISHED"
  },
  "containers": {
    "cna": {
      "providerMetadata": {
        "orgId": "53f830b8-0a3f-465b-8143-3b8a9948e749",
        "shortName": "redhat",
        "dateUpdated": "2026-03-26T20:06:28.313Z"
      },
      "datePublic": "2026-02-10T18:47:15.531Z",
      "title": "Libssh: buffer underflow in ssh_get_hexa() on invalid input",
      "descriptions": [
        {
          "lang": "en",
          "value": "The API function `ssh_get_hexa()` is vulnerable, when 0-lenght\ninput is provided to this function. This function is used internally\nin `ssh_get_fingerprint_hash()` and `ssh_print_hexa()` (deprecated),\nwhich is vulnerable to the same input (length is provided by the\ncalling application).\n\nThe function is also used internally in the gssapi code for logging\nthe OIDs received by the server during GSSAPI authentication. This\ncould be triggered remotely, when the server allows GSSAPI authentication\nand logging verbosity is set at least to SSH_LOG_PACKET (3). This\ncould cause self-DoS of the per-connection daemon process."
        }
      ],
      "affected": [
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 10",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "libssh",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:10"
          ],
          "defaultStatus": "affected"
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 6",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "libssh2",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:6"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 7",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "libssh2",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:7"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 8",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "libssh",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:8"
          ],
          "defaultStatus": "affected"
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat Enterprise Linux 9",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "libssh",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:9"
          ],
          "defaultStatus": "affected"
        },
        {
          "vendor": "Red Hat",
          "product": "Red Hat OpenShift Container Platform 4",
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "packageName": "rhcos",
          "cpes": [
            "cpe:/a:redhat:openshift:4"
          ],
          "defaultStatus": "affected"
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "lang": "en",
              "description": "Buffer Underwrite ('Buffer Underflow')",
              "cweId": "CWE-124",
              "type": "CWE"
            }
          ]
        }
      ],
      "references": [
        {
          "url": "https://access.redhat.com/security/cve/CVE-2026-0966",
          "tags": [
            "vdb-entry",
            "x_refsource_REDHAT"
          ]
        },
        {
          "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2433121",
          "name": "RHBZ#2433121",
          "tags": [
            "issue-tracking",
            "x_refsource_REDHAT"
          ]
        }
      ],
      "metrics": [
        {},
        {
          "format": "CVSS",
          "cvssV3_0": {
            "version": "3.0",
            "vectorString": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L",
            "attackVector": "NETWORK",
            "attackComplexity": "LOW",
            "privilegesRequired": "NONE",
            "userInteraction": "NONE",
            "scope": "UNCHANGED",
            "confidentialityImpact": "NONE",
            "integrityImpact": "LOW",
            "availabilityImpact": "LOW",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM"
          }
        }
      ],
      "workarounds": [
        {
          "lang": "en",
          "value": "To mitigate this issue, consider disabling GSSAPI authentication if it is not required, or reduce the `LogLevel` in the `sshd_config` file to a value lower than `SSH_LOG_PACKET` (e.g., `INFO`).\n\nTo disable GSSAPI authentication, add or modify the following line in `/etc/ssh/sshd_config`:\n`GSSAPIAuthentication no`\n\nTo reduce logging verbosity, add or modify the following line in `/etc/ssh/sshd_config`:\n`LogLevel INFO`\n\nAfter making changes to `sshd_config`, the `sshd` service must be restarted for the changes to take effect. This may temporarily interrupt active SSH sessions."
        }
      ],
      "timeline": [
        {
          "time": "2026-01-26T23:14:46.617Z",
          "lang": "en",
          "value": "Reported to Red Hat."
        },
        {
          "time": "2026-02-10T18:47:15.531Z",
          "lang": "en",
          "value": "Made public."
        }
      ],
      "credits": [
        {
          "lang": "en",
          "value": "Red Hat would like to thank Jakub Jelen (libssh), Jun Xu, Kang Yang, and Yunhang Zhang for reporting this issue."
        }
      ]
    }
  }
}