{"id":"CVE-2026-55581","state":"PUBLISHED","title":"mcp-shell: Secure Mode Allowlist Bypass via Default `/bin/bash` Executable","description":"mcp-shell is an MCP server for running shell commands securely, auditably, and on demand. Prior to 0.6.0, the default Docker security.yaml includes /bin/bash in allowed_executables, while security.go validates only the first token and checkBlockedPatternsAndCommands does not reject the shell command-mode flag -c. A caller of the shell_exec MCP tool can provide the command argument `/bin/bash -c <arbitrary-command>`, which passes validation and reaches executor.go, where parseCommand and exec.CommandContext execute the arbitrary command as mcpuser outside the intended allowlist. This issue is fixed in version 0.6.0.","publishedAt":"2026-08-25T15:40:10.992Z","updatedAt":"2026-08-25T19:01:56.083Z","severity":{"score":8.4,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["sonirico mcp-shell"],"affected":[{"vendor":"sonirico","product":"mcp-shell","versions":[{"version":"< 0.6.0","status":"affected"}]}],"references":["https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3","https://github.com/sonirico/mcp-shell/pull/16","https://github.com/sonirico/mcp-shell/commit/f31377fce6ec31114e5a4398c0e5270552bce09f","https://github.com/sonirico/mcp-shell/releases/tag/v0.6.0"],"weaknesses":["CWE-78","CWE-183","CWE-1188"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/55xxx/CVE-2026-55581.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-55581","state":"PUBLISHED","datePublished":"2026-08-25T15:40:10.992Z","dateUpdated":"2026-08-25T19:01:56.083Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-16T23:18:03.169Z"},"containers":{"cna":{"title":"mcp-shell: Secure Mode Allowlist Bypass via Default `/bin/bash` Executable","descriptions":[{"lang":"en","value":"mcp-shell is an MCP server for running shell commands securely, auditably, and on demand. Prior to 0.6.0, the default Docker security.yaml includes /bin/bash in allowed_executables, while security.go validates only the first token and checkBlockedPatternsAndCommands does not reject the shell command-mode flag -c. A caller of the shell_exec MCP tool can provide the command argument `/bin/bash -c <arbitrary-command>`, which passes validation and reaches executor.go, where parseCommand and exec.CommandContext execute the arbitrary command as mcpuser outside the intended allowlist. This issue is fixed in version 0.6.0."}],"affected":[{"vendor":"sonirico","product":"mcp-shell","versions":[{"version":"< 0.6.0","status":"affected"}]}],"references":[{"url":"https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3","name":"https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/sonirico/mcp-shell/pull/16","name":"https://github.com/sonirico/mcp-shell/pull/16","tags":["x_refsource_MISC"]},{"url":"https://github.com/sonirico/mcp-shell/commit/f31377fce6ec31114e5a4398c0e5270552bce09f","name":"https://github.com/sonirico/mcp-shell/commit/f31377fce6ec31114e5a4398c0e5270552bce09f","tags":["x_refsource_MISC"]},{"url":"https://github.com/sonirico/mcp-shell/releases/tag/v0.6.0","name":"https://github.com/sonirico/mcp-shell/releases/tag/v0.6.0","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"LOCAL","availabilityImpact":"HIGH","baseScore":8.4,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-78","lang":"en","description":"CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-183","lang":"en","description":"CWE-183: Permissive List of Allowed Inputs","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-1188","lang":"en","description":"CWE-1188: Insecure Default Initialization of Resource","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-25T15:40:10.992Z"},"source":{"advisory":"GHSA-3x77-wg38-92r3","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/sonirico/mcp-shell/security/advisories/GHSA-3x77-wg38-92r3","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-25T19:01:36.178820Z","id":"CVE-2026-55581","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-25T19:01:56.083Z"}}]}}}