CVE-2026-19820 (GCVE-0-2026-19820)
Vulnerability from cvelistv5 – Published: 2026-09-01 00:13 – Updated: 2026-09-01 00:13
VLAI
EPSS
VEX
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
Assigner
References
2 references
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 |
{
"containers": {
"cna": {
"affected": [
{
"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"
}
]
}
],
"credits": [
{
"lang": "en",
"type": "coordinator",
"value": "TrendAI Zero Day Initiative"
},
{
"lang": "en",
"type": "finder",
"value": "hamdi"
}
],
"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."
}
],
"metrics": [
{
"cvssV4_0": {
"baseScore": 5.8,
"baseSeverity": "MEDIUM",
"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",
"version": "4.0"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"description": "CWE-59 Improper Link Resolution Before File Access",
"lang": "en"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-01T00:13:03.935Z",
"orgId": "4ac701fe-44e9-4bcd-9585-dd6449257611",
"shortName": "Bugcrowd"
},
"references": [
{
"url": "https://www.backblaze.com/computer-backup/docs/backup-client-release-notes-windows"
},
{
"url": "https://www.backblaze.com/status/update"
}
],
"title": "Backblaze Client for Windows Improper Link Resolution Vulnerability"
}
},
"cveMetadata": {
"assignerOrgId": "4ac701fe-44e9-4bcd-9585-dd6449257611",
"assignerShortName": "Bugcrowd",
"cveId": "CVE-2026-19820",
"datePublished": "2026-09-01T00:13:03.935Z",
"dateReserved": "2026-08-14T05:28:19.979Z",
"dateUpdated": "2026-09-01T00:13:03.935Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-19820",
"date": "2026-09-01",
"epss": "0.00327",
"percentile": "0.25278"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-19820\",\"sourceIdentifier\":\"4ac701fe-44e9-4bcd-9585-dd6449257611\",\"published\":\"2026-09-01T01:16:33.137\",\"lastModified\":\"2026-09-01T01:16:33.137\",\"vulnStatus\":\"Received\",\"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.\"}],\"affected\":[{\"source\":\"4ac701fe-44e9-4bcd-9585-dd6449257611\",\"affectedData\":[{\"vendor\":\"Backblaze\",\"product\":\"Backblaze Client\",\"defaultStatus\":\"unaffected\",\"platforms\":[\"Windows\"],\"versions\":[{\"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\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV40\":[{\"source\":\"4ac701fe-44e9-4bcd-9585-dd6449257611\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"4.0\",\"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\",\"baseScore\":7.8,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"attackRequirements\":\"NONE\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"vulnConfidentialityImpact\":\"NONE\",\"vulnIntegrityImpact\":\"NONE\",\"vulnAvailabilityImpact\":\"NONE\",\"subConfidentialityImpact\":\"HIGH\",\"subIntegrityImpact\":\"LOW\",\"subAvailabilityImpact\":\"LOW\",\"exploitMaturity\":\"NOT_DEFINED\",\"confidentialityRequirement\":\"NOT_DEFINED\",\"integrityRequirement\":\"NOT_DEFINED\",\"availabilityRequirement\":\"NOT_DEFINED\",\"modifiedAttackVector\":\"NOT_DEFINED\",\"modifiedAttackComplexity\":\"NOT_DEFINED\",\"modifiedAttackRequirements\":\"NOT_DEFINED\",\"modifiedPrivilegesRequired\":\"NOT_DEFINED\",\"modifiedUserInteraction\":\"NOT_DEFINED\",\"modifiedVulnConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedVulnIntegrityImpact\":\"NOT_DEFINED\",\"modifiedVulnAvailabilityImpact\":\"NOT_DEFINED\",\"modifiedSubConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedSubIntegrityImpact\":\"NOT_DEFINED\",\"modifiedSubAvailabilityImpact\":\"NOT_DEFINED\",\"Safety\":\"NOT_DEFINED\",\"Automatable\":\"NOT_DEFINED\",\"Recovery\":\"NOT_DEFINED\",\"valueDensity\":\"NOT_DEFINED\",\"vulnerabilityResponseEffort\":\"NOT_DEFINED\",\"providerUrgency\":\"NOT_DEFINED\"}}]},\"references\":[{\"url\":\"https://www.backblaze.com/computer-backup/docs/backup-client-release-notes-windows\",\"source\":\"4ac701fe-44e9-4bcd-9585-dd6449257611\"},{\"url\":\"https://www.backblaze.com/status/update\",\"source\":\"4ac701fe-44e9-4bcd-9585-dd6449257611\"}]}}"
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
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.
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