Vulnerability-Lookup

CVE-2026-19820 (GCVE-0-2026-19820)

Vulnerability from cvelistv5 – Published: 2026-09-01 00:13 – Updated: 2026-09-01 15:14

Title

Backblaze Client for Windows Improper Link Resolution Vulnerability

Summary

A vulnerability in the Backblaze Client allows a local user to make the system not bootable by creating a link from Backblaze's folder to Windows OS system files during a backup. Successful exploitation requires an administrator-level system change that results in the absence of specific Windows OS security controls. This vulnerability is due to improper link resolution.

Severity

5.8 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-01 15:13 UTC

CWE

CWE-59 Improper Link Resolution Before File Access
CWE-59 - Improper Link Resolution Before File Access ('Link Following')

Assigner

Bugcrowd mitre root

References

2 references

URL	Tags
https://www.backblaze.com/computer-backup/docs/ba…
https://www.backblaze.com/status/update

Impacted products

1 product

Vendor	Product	Version	CPE status
Backblaze	Backblaze Client	Affected: 10.0.0.1029 (custom) Affected: 10.0.1.10307 (custom) Affected: 10.0.2.1047 (custom)	guessed

Credits

TrendAI Zero Day Initiative hamdi

Show details on NVD website

JSON

To clipboard

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                "id": "CVE-2026-19820",
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FKIE_CVE-2026-19820

Vulnerability from fkie_nvd - Published: 2026-09-01 01:16 - Updated: 2026-09-01 16:16

Severity

7.8 (High) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L

Summary

References

	URL	Tags
	4ac701fe-44e9-4bcd-9585-dd6449257611	https://www.backblaze.com/computer-backup/docs/backup-client-release-notes-windows
	4ac701fe-44e9-4bcd-9585-dd6449257611	https://www.backblaze.com/status/update

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "platforms": [
            "Windows"
          ],
          "product": "Backblaze Client",
          "vendor": "Backblaze",
          "versions": [
            {
              "status": "affected",
              "version": "10.0.0.1029",
              "versionType": "custom"
            },
            {
              "status": "affected",
              "version": "10.0.1.10307",
              "versionType": "custom"
            },
            {
              "status": "affected",
              "version": "10.0.2.1047",
              "versionType": "custom"
            }
          ]
        }
      ],
      "source": "4ac701fe-44e9-4bcd-9585-dd6449257611"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "A vulnerability in the Backblaze Client allows a local user to make the system not bootable by creating a link from Backblaze\u0027s folder to Windows OS system files during a backup. Successful exploitation requires an administrator-level system change that results in the absence of specific Windows OS security controls. This vulnerability is due to improper link resolution."
    }
  ],
  "id": "CVE-2026-19820",
  "lastModified": "2026-09-01T16:16:55.223",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "LOW",
          "subConfidentialityImpact": "HIGH",
          "subIntegrityImpact": "LOW",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "4ac701fe-44e9-4bcd-9585-dd6449257611",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
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        "ssvcData": {
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    },
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  ]
}

GHSA-WF7J-R93F-5CVM

Vulnerability from github – Published: 2026-09-01 03:31 – Updated: 2026-09-01 03:31

Details

Severity

7.8 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-19820"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-59"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-01T01:16:33Z",
    "severity": "HIGH"
  },
  "details": "A vulnerability in the Backblaze Client allows a local user to make the system not bootable by creating a link from Backblaze\u0027s folder to Windows OS system files during a backup. Successful exploitation requires an administrator-level system change that results in the absence of specific Windows OS security controls. This vulnerability is due to improper link resolution.",
  "id": "GHSA-wf7j-r93f-5cvm",
  "modified": "2026-09-01T03:31:03Z",
  "published": "2026-09-01T03:31:03Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-19820"
    },
    {
      "type": "WEB",
      "url": "https://www.backblaze.com/computer-backup/docs/backup-client-release-notes-windows"
    },
    {
      "type": "WEB",
      "url": "https://www.backblaze.com/status/update"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-19820 (GCVE-0-2026-19820)

FKIE_CVE-2026-19820

GHSA-WF7J-R93F-5CVM

Tags

Sightings

Nomenclature