# CVE-2026-25551: Seagull Software BarTender Deserialization Privilege Escalation via .NET Remoting Service

> Local attackers can exploit insecure .NET Remoting deserialization in BarTender to execute arbitrary code with SYSTEM privileges.

- **Severity:** High 8.5 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Jun 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-g42f-xxvf-qj27

## What is CVE-2026-25551?

CVE-2026-25551 is a high-severity unsafe deserialization vulnerability in Seagull Software, LLC. BarTender 2021, published on 4 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Seagull Software BarTender 2021 R1 through 12.0.1 contains an insecure deserialization vulnerability that allows low-privileged local users to escalate privileges. The DataServiceSingleton .NET Remoting endpoint is bound to localhost on TCP port 7375 via BtSystem.Service.exe, limiting the attack surface to local access only. The endpoint is configured with BinaryServerFormatterSinkProvider and TypeFilterLevel set to Full. A low-privileged local attacker can send YSoSerial.NET-generated BinaryFormatter payloads to the localhost-bound endpoint to achieve code execution as NT AUTHORITY\\\\SYSTEM. The vulnerability was corrected in BarTender 12.1, released on August 14, 2026. Users should upgrade to BarTender 12.1 or later.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-25551?


## How do I fix CVE-2026-25551?

No fix has been published for CVE-2026-25551 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-25551 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25551 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25551 and fix it if it is affected.

What it is: CVE-2026-25551 is a high-severity unsafe deserialization vulnerability in Seagull Software, LLC. BarTender 2021, published on 4 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25551 exists.

Affected product: Seagull Software, LLC. BarTender 2021. 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-2026-25551/ (Markdown: https://insights.sbomify.com/CVE-2026-25551/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25551
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25551
- OSV: https://osv.dev/vulnerability/CVE-2026-25551

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-25551/
Summaries are generated and may contain mistakes; the official description above is the record.