# CVE-2026-28198: Privilege Escalation via Cryptographic Signature Verification Bypass in NetBackup Flex OS Shell

> Authenticated low-privileged users can bypass signature verification to gain root access on NetBackup Flex OS appliances.

- **Severity:** Critical 9.4 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** GHSA-h4hc-x5f6-wfc4

## What is CVE-2026-28198?

CVE-2026-28198 is a critical vulnerability in Cohesity NetBackup Flex OS, published on 18 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

An authenticated, low-privileged user with access to the NetBackup Flex 
OS management shell could bypass the cryptographic signature 
verification step of a privileged support command by supplying a 
specially formed access credential. Successful exploitation grants the 
attacker an unrestricted root shell with full control over the Flex 
appliance host and all hosted containers, completely compromising 
confidentiality, integrity, and availability.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-28198?


## How do I fix CVE-2026-28198?

No fix has been published for CVE-2026-28198 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-28198 being exploited?

There is no known exploitation of CVE-2026-28198 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28198 and fix it if it is affected.

What it is: CVE-2026-28198 is a critical vulnerability in Cohesity NetBackup Flex OS, published on 18 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-28198 in the wild and no public exploit code.

Affected product: Cohesity NetBackup Flex OS. 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-2026-28198/ (Markdown: https://insights.sbomify.com/CVE-2026-28198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28198
- OSV: https://osv.dev/vulnerability/CVE-2026-28198

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28198/
Summaries are generated and may contain mistakes; the official description above is the record.