5.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-49406

CVE-2026-49406: Deno: BYONM module resolution allows `package.json` main path traversal to bypass `--allow-read` restrictions

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.12, when Deno was run in BYONM mode (nodeModulesDir: "manual"), the module resolver did not validate that a package's resolved entrypoint stayed within its node_modules/<pkg>/ directory. A malicious package.json whose main field contained .. segments was able to resolve to an arbitrary path on disk, and the resolver then read that file without consulting the --allow-read allowlist. This let a require("evil-pkg") call return the contents of a file that a direct Deno.readTextFileSync(...) call would have been blocked from reading. This vulnerability is fixed in 2.7.12.

(GitHub Advisory)

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CVE-2026-49406

CVE-2026-49406:

5.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation pocAutomatable NoTech Impact Partial

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
deno	rust	<= 2.7.11	2.7.12

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is a path traversal weakness in Deno's "Bring Your Own Node Modules" (BYONM) feature. When a user calls require() on an npm package, Deno's module resolver reads the main field of the package's package.json to find the entrypoint. A malicious package could craft a main field with ../ sequences to point to a file outside of its own directory. The vulnerable code would resolve this path and read the file, bypassing Deno's --allow-read permission checks.

The analysis identified the fixing commit by comparing the git tags of the last vulnerable version (v2.7.11) and the first patched version (v2.7.12). The key commit, 8295a2cf2aabe2ecd9ccce8a802d0d5d61095a2e, is explicitly titled "fix(node): validate resolved main path stays within package directory".

This commit patched the vulnerability in two places:

ext/node/polyfills/01_require.js: In the JavaScript implementation of require, the tryPackage function was modified to add a check ensuring the resolved path of the main entry does not escape the package's root directory.
libs/node_resolver/resolution.rs: In the core Rust implementation, the function legacy_main_resolve (as identified from the commit message) within the NpmPackageResolver was updated to validate the resolved path. It now checks if the resolved path guess still starts with the package_path, preventing traversal.

Both of these functions are directly responsible for processing the malicious package.json and were the points where the path traversal was possible. An exploit would trigger these functions, making them key indicators in a runtime profile.

Vulnerable functions

tryPackage

ext/node/polyfills/01_require.js

This function is part of the JavaScript polyfill for Node.js's `require`. It resolves the `main` field from a `package.json` file. The vulnerability existed because this function did not validate whether the resolved path traversed outside of the package's directory, allowing a malicious `package.json` to cause the module loader to read arbitrary files on the filesystem.

deno_node_resolver::resolution::NpmPackageResolver::legacy_main_resolve

libs/node_resolver/resolution.rs

This Rust function is the core native implementation for resolving the `main` entry in a `package.json` file for the Node.js compatibility layer. It was vulnerable to a path traversal attack because it would construct a file path based on the `main` field without ensuring the path remained within the package's boundaries. This allowed a malicious package to access files outside of the intended directory and bypass `--allow-read` restrictions.

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WAF Protection Rules

WAF Rule

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Reasoning

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