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Vulnerability record · CVE-2026-81097 · published 27 August 2026

CVE-2026-81097: OS command injection vulnerability

The execute_ruby tool is documented as a read-only Ruby sandbox and is enforced by a pattern denylist together with replacements for the process-spawning methods on Kernel. The pseudo-terminal library's spawn entry points are neither in the denylist nor replaced, so a normal tool call could reach them and start a shell, executing commands as the account running the server and outside the guarded methods. The denylist was introduced with the tool in 1.4.0 and never covered those entry points through 1.6.0. Version 1.6.1 restricts the requires the sandbox permits to a data-only list and blocks dynamic dispatch to execution entry points; 2.0.0 removes the tool.

8.6 CVSS 4.0 High EPSS 0.24% · top 87.0% CWE-78 · OS command injection Deferred
8.6CVSS 4.0 base score
0.24%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
24 Sep 2026Last modified by NVD

Description

The execute_ruby tool is documented as a read-only Ruby sandbox and is enforced by a pattern denylist together with replacements for the process-spawning methods on Kernel. The pseudo-terminal library's spawn entry points are neither in the denylist nor replaced, so a normal tool call could reach them and start a shell, executing commands as the account running the server and outside the guarded methods. The denylist was introduced with the tool in 1.4.0 and never covered those entry points through 1.6.0. Version 1.6.1 restricts the requires the sandbox permits to a data-only list and blocks dynamic dispatch to execution entry points; 2.0.0 removes the tool.

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/maquina-app/rails-mcp-server
https://github.com/maquina-app/rails-mcp-server/pull/59
https://github.com/maquina-app/rails-mcp-server/releases
https://www.vulncheck.com/advisories/rails-mcp-server-1.4.0-through-1.6.0-os-command-execution-via-execute-ruby-pty-esca

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Source: NIST National Vulnerability Database (record CVE-2026-81097), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.