MOKSHA-2026-0022

Vulnerability from moksha – Published: 2026-04-24 06:00 – Updated:
VLAI
Title
Real-Time I/O Class Abuse via VBD.qos_algorithm_params - Cross-VM Starvation
Summary
A user with the vm-admin role in XAPI-based hypervisors (XenServer, XCP-ng) can set the real-time I/O scheduling class on VBD kernel threads by writing sched=rt and class=highest to VBD.qos_algorithm_params. xenopsd invokes ionice -c1 -n0 on the affected threads, granting strict priority over all best-effort and idle I/O on the host. This starves I/O for every other VM on the same host. The change takes effect immediately without VBD replug and produces no security alert.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
8.3 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N
CWE
  • CWE-862 - Missing Authorization
  • CWE-20 - Improper Input Validation
References
Impacted products
Credits
Jakob Wolffhechel, Moksha
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "XenServer",
          "vendor": "Cloud Software Group",
          "versions": [
            {
              "status": "affected",
              "version": "all",
              "versionType": "custom"
            }
          ]
        },
        {
          "product": "XCP-ng",
          "vendor": "Vates",
          "versions": [
            {
              "status": "affected",
              "version": "all",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Jakob Wolffhechel, Moksha"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "A user with the vm-admin role in XAPI-based hypervisors (XenServer, XCP-ng) can set the real-time I/O scheduling class on VBD kernel threads by writing sched=rt and class=highest to VBD.qos_algorithm_params. xenopsd invokes ionice -c1 -n0 on the affected threads, granting strict priority over all best-effort and idle I/O on the host. This starves I/O for every other VM on the same host. The change takes effect immediately without VBD replug and produces no security alert."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H",
            "version": "3.1"
          },
          "format": "CVSS"
        },
        {
          "cvssV4_0": {
            "baseScore": 8.3,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N",
            "version": "4.0"
          },
          "format": "CVSS"
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-862",
              "description": "Missing Authorization",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-20",
              "description": "Improper Input Validation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-24T06:00:00Z",
        "orgId": "moksha.dk",
        "shortName": "Moksha"
      },
      "references": [
        {
          "url": "https://cna.moksha.dk/MOKSHA-2026-0022"
        }
      ],
      "title": "Real-Time I/O Class Abuse via VBD.qos_algorithm_params - Cross-VM Starvation"
    }
  },
  "cveMetadata": {
    "alternateIds": [
      "GCVE-117-2026-0022"
    ],
    "assignerOrgId": "moksha.dk",
    "cveId": "MOKSHA-2026-0022",
    "datePublished": "2026-04-24T06:00:00Z",
    "state": "PUBLISHED",
    "x_moksha_note": "Self-issued advisory. MOKSHA-2026-NNNN is not a MITRE CVE ID. Schema follows CVE JSON 5.1 for tooling compatibility. alternateIds contains GCVE cross-references (GNA #117) and will also carry MITRE CVE IDs if assigned."
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1"
}



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