Backblaze Client for Windows Improper Link Resolution Vulnerability

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-19820
StatePUBLISHED
AssignerBugcrowd
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-01 01:16:33 UTC
Updated2026-09-01 01:16:33 UTC
DescriptionA 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.

Risk And Classification

Primary CVSS: v4.0 7.8 HIGH from 4ac701fe-44e9-4bcd-9585-dd6449257611

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

Problem Types: CWE-59 Improper Link Resolution Before File Access

VersionSourceTypeScoreSeverityVector
4.04ac701fe-44e9-4bcd-9585-dd6449257611Secondary7.8HIGHCVSS: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/C...
4.0CNACVSS5.8MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:L

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
None
Sub Conf.
High
Sub Integrity
Low
Sub Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Backblaze Backblaze Client affected 10.0.0.1029 custom Windows
CNA Backblaze Backblaze Client affected 10.0.1.10307 custom Windows
CNA Backblaze Backblaze Client affected 10.0.2.1047 custom Windows

References

ReferenceSourceLinkTags
www.backblaze.com/status/update 4ac701fe-44e9-4bcd-9585-dd6449257611 www.backblaze.com
www.backblaze.com/computer-backup/docs/backup-client-release-notes-windows 4ac701fe-44e9-4bcd-9585-dd6449257611 www.backblaze.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: TrendAI Zero Day Initiative (en)

CNA: hamdi (en)

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