# CVE-2026-19820: Backblaze Client for Windows Improper Link Resolution Vulnerability

> A local attacker can render the system unbootable by exploiting improper link resolution during backup, requiring specific administrative configuration changes.

- **Severity:** Medium 5.8 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** GHSA-wf7j-r93f-5cvm

## What is CVE-2026-19820?

CVE-2026-19820 is a medium-severity path traversal vulnerability in Backblaze Client, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2026-19820?


## How do I fix CVE-2026-19820?

No fix has been published for CVE-2026-19820 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-19820 being exploited?

There is no known exploitation of CVE-2026-19820 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19820 and fix it if it is affected.

What it is: CVE-2026-19820 is a medium-severity path traversal vulnerability in Backblaze Client, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-19820 in the wild and no public exploit code.

Affected product: Backblaze Client. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-19820/ (Markdown: https://insights.sbomify.com/CVE-2026-19820/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19820
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19820
- OSV: https://osv.dev/vulnerability/CVE-2026-19820

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19820/
Summaries are generated and may contain mistakes; the official description above is the record.