CVE-2026-10278: Path Traversal in ishayoyo excel-mcp – Exploitation, Detection, and Remediation

Technical summary

CVE-2026-10278 is a path traversal flaw (CWE-22) in ishayoyo's excel-mcp library affecting versions through 1.0.2. The vulnerability resides in the read_file and write_file functions within src/index.ts, where insufficient validation of the filePath and outputPath parameters permits directory traversal sequences (e.g., '../../../') to bypass access controls. The CVSS v3.1 score of 6.3 reflects a network-accessible attack requiring valid authentication, with potential impact to confidentiality, integrity, and availability. The vulnerability is remotely exploitable and public disclosure has occurred without a corresponding patch from the maintainers.

Business impact

Organizations deploying excel-mcp risk unauthorized file access and modification through authenticated sessions. An insider or compromised account holder could exfiltrate sensitive spreadsheets, configuration files, or database credentials stored on the same filesystem. Similarly, attackers could overwrite application files to inject malicious code or disable services. For teams using excel-mcp in API gateways, data processing pipelines, or collaborative environments, this vulnerability can compromise data confidentiality and operational integrity without direct network compromise.

Affected systems

The ishayoyo excel-mcp project versions 1.0.2 and earlier are affected. No vendor patches have been released as of the publication date. Organizations using this library in production environments—particularly those integrating it into server-side applications, REST APIs, or automated data workflows—should inventory their deployments immediately. The lack of vendor response increases exposure duration.

Exploitability

The vulnerability is remotely exploitable over the network by any user with valid authentication credentials. Public disclosure of this flaw removes the requirement for vulnerability research, lowering the barrier for exploitation. While the attack requires prior authentication (a limiting factor), the simplicity of path traversal techniques and the public nature of the disclosure elevate practical risk. No exploit code weaponization is required; standard path traversal payloads can trigger the flaw.

Remediation

Immediate action: audit your codebase for excel-mcp dependencies and version pinning. Remove or isolate excel-mcp from production environments if possible. Contact the ishayoyo project maintainers directly to request an expedited patch. Apply input validation on all file path parameters to reject or sanitize directory traversal sequences (../, ..\ and encoded variants). Implement filesystem access controls using chroot jails, containerization, or OS-level file permissions to limit the scope of readable/writable directories. Upgrade to a patched version as soon as the maintainers release one; monitor the project repository for updates.

Patch guidance

Verify the ishayoyo excel-mcp project repository and release notes for patched versions exceeding 1.0.2. At publication, no official patch exists; establish a monitoring process for the project's GitHub or package registry (npm, if applicable). If a patch is released, upgrade immediately and validate the fix by reviewing commit diffs to confirm input validation improvements. Until patching, consider temporary mitigations: restrict excel-mcp to isolated, non-production environments, or refactor dependent code to use alternative, actively maintained libraries.

Detection guidance

Monitor logs for unexpected file access patterns via excel-mcp functions, particularly those involving parent directory references (../) or absolute paths outside the application root. Implement egress controls to detect exfiltration of sensitive files accessed through the library. Audit authentication logs for unusual session activity or access times. Deploy file integrity monitoring (FIM) on configuration and application directories to detect unauthorized modification. Network-based detection is limited; focus on application logging and host-based controls.

Why prioritize this

Although not yet on CISA's KEV list, this vulnerability merits high prioritization due to public disclosure, ease of exploitation for authenticated users, and current lack of vendor patches. The authenticated-only requirement prevents it from reaching critical severity, but organizations relying on excel-mcp should treat this as urgent, especially if the library processes sensitive data. The 6.3 CVSS score accurately reflects medium severity with meaningful business impact.

Risk score, explained

The CVSS v3.1 score of 6.3 (MEDIUM) is calculated from: AV:N (Network—remotely accessible), AC:L (Low Attack Complexity—standard path traversal), PR:L (Low Privilege Required—valid authentication necessary), UI:N (No User Interaction), S:U (Unchanged Scope), C:L (Low Confidentiality Impact—file read access), I:L (Low Integrity Impact—file write access), A:L (Low Availability Impact—potential service disruption via file corruption). The 'L' impact ratings reflect the confined nature of the attack but acknowledge real risk to confidentiality, integrity, and availability within the file system's accessible scope.

Frequently asked questions