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excel-mcp-server CVE-2026-85661

| EUVDEUVD-2026-71117 CRITICAL
Path Traversal (CWE-22)
2026-09-04 VulnCheck GHSA-xv88-r947-5c3v
9.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
9.3 CRITICAL
CVSS:4.0/AV:N/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:X/V:X/RE:X/U:X
vuln.today AI
8.4 HIGH

Stdio mode is a locally-driven process so AV:L; no auth or interaction gate the tool calls (PR:N/UI:N); arbitrary read and write yield C:H/I:H and file overwrite supports A:H.

3.1 AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Analysis Generated
Sep 04, 2026 - 15:39 vuln.today
CVE Published
Sep 04, 2026 - 14:32 cve.org
CRITICAL 9.3

DescriptionCVE.org

excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when EXCEL_FILES_PATH is unset, allowing attackers to read and write arbitrary files. Attackers can supply unchecked file paths to read and write tools to access any file accessible to the process.

AnalysisAI

Arbitrary file read and write in excel-mcp-server 0.1.8 lets attackers escape the intended Excel workspace when the server runs in stdio mode with the EXCEL_FILES_PATH environment variable unset. Because path confinement is not enforced, unchecked absolute or traversal paths passed to the read and write tools reach any file the server process can access, enabling disclosure of secrets and overwrite of arbitrary files (CWE-22). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
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Delivery
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Exploit
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Execution
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Impact
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Vulnerability AssessmentAI

Exploitation Requires the server to be running in stdio transport mode AND the EXCEL_FILES_PATH environment variable to be unset (its intended sandbox root); under these conditions the read and write tools accept unchecked absolute or ../ traversal paths and operate on any file accessible to the server process. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The supplied CVSS 4.0 vector (9.3, AV:N/AC:L/PR:N/UI:N/VC:H/VI:H/VA:H) rates this critical, but the AV:N network assessment is in tension with the described precondition: exploitation applies to stdio transport mode, which is a local process driven by a local client, so a local/adjacent vector (AV:L) is more defensible - verify transport assumptions with the vendor. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation No vendor-released patched version is identified in the provided data (upstream tracking exists in issue #149 but no fixed tag is confirmed) - treat as No vendor-released patch identified at time of analysis and monitor the repository for a release above 0.1.8. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, identify all systems running excel-mcp-server 0.1.8, particularly those deployed in stdio mode without EXCEL_FILES_PATH set; immediately set the EXCEL_FILES_PATH environment variable to a restricted directory to confine file access scope. …

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CVE-2026-85661 vulnerability details – vuln.today

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