What is CVE-2026-25551?

CVE-2026-25551 is a high-severity vulnerability in Seagull Software, Llc. Bartender 2021, classified under Deserialization of Untrusted Data. CVSS score: 7.8/10. Published 2026-06-04.

How severe is CVE-2026-25551?

High severity. CVSS v3 base score is 7.8 out of 10.

Deserialization in Seagull Software, Llc. Bartender 2021

CVE-2026-25551

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.

Vulnerability class: Insecure Deserialization

Published 2026-06-04 · last modified 2026-09-02.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (27.3th percentile), scored 2026-10-07.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 27.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.004 · change: +0.002

Affected products

Seagull Software, Llc. Bartender 2021 — versions R1

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

gist.github.com/VAMorales/dde5b1c0415a8505ccd6fafdb095a618 (technical-description, exploit)
portal.seagullscientific.com/downloads/bartender (product)
www.vulncheck.com/advisories/seagull-software-bartender-deserialization-privile… (third-party-advisory)
trust.seagullsoftware.com/ (vendor-advisory, patch)

Frequently asked questions

What is CVE-2026-25551?: CVE-2026-25551 is a high-severity vulnerability in Seagull Software, Llc. Bartender 2021, classified under Deserialization of Untrusted Data. CVSS score: 7.8/10. Published 2026-06-04.
How severe is CVE-2026-25551?: High severity. CVSS v3 base score is 7.8 out of 10.