CVE-2026-49401

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.14, Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file. That means a program could reach a denied path by spelling it differently than the deny rule. This vulnerability is fixed in 2.7.14.

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.14, Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file. That means a program could reach a denied path by spelling it differently than the deny rule. This vulnerability is fixed in 2.7.14.

Summary

Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file.

That means a program could reach a denied path by spelling it differently than the deny rule. For example, with --deny-read=/secrets/passwörter.txt, a script could still read the file by opening /secrets/passwo\u0308rter.txt (NFD instead of NFC), or /SECRETS/PASSWÖRTER.txt (different case, since default APFS volumes are case-insensitive). Other forms include ligature characters (fi vs fi, ff vs ff, …) and German ß vs ss.

The denied path and the requested path differed at the byte level, so Deno's permission check passed; the kernel then resolved them to the same inode and served the file anyway. The same flaw affected --deny-write, --deny-run, and --deny-ffi, which share the same path-comparison code.

Am I affected?

You are potentially affected if all of the following are true:

1. You run Deno on macOS (the issue is specific to APFS path-equivalence rules; Linux and Windows are not affected by this variant).
2. You rely on --deny-read, --deny-write, --deny-run, or --deny-ffi as a security boundary against less-trusted code — a dependency, plugin, or attacker-controlled input.
3. The protected path contains characters that have alternate Unicode spellings — most commonly accented characters (é, ñ, ö, …), German ß, or Latin ligatures — or you rely on case-sensitivity on a default APFS volume.

If you only run fully trusted code, or your deny rules cover paths that are pure ASCII with no case-sensitive aliases, you are not exposed to this specific bypass.

Impact

A program running with broad --allow-read (or --allow-write / --allow-run / --allow-ffi) but with --deny-* carve-outs for specific paths could read, write, execute, or load via FFI those denied paths by referring to them through a Unicode- or case-equivalent spelling. The sandbox model on macOS was weaker than the flags suggested.

Workaround

If you cannot upgrade immediately:

• Prefer --allow-* allowlists over --deny-* denylists. Allow rules match against the original specifier, so an attacker-supplied alternate spelling will not match a path you didn't explicitly grant.
• Do not rely on case-sensitivity of paths on macOS for security boundaries; default APFS volumes are case-insensitive.

Fix

On macOS, Deno now normalizes both the deny-rule path and the requested path to NFC and applies Unicode case folding before comparing them. This matches how APFS resolves paths at the inode level, so byte-different but equivalent spellings are now rejected by the same deny rule.

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.14, Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file. That means a program could reach a denied path by spelling it differently than the deny rule. This vulnerability is fixed in 2.7.14.

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.14, Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file. That means a program could reach a denied path by spelling it differently than the deny rule. This vulnerability is fixed in 2.7.14.

Summary

Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file.

That means a program could reach a denied path by spelling it differently than the deny rule. For example, with --deny-read=/secrets/passwörter.txt, a script could still read the file by opening /secrets/passwo\u0308rter.txt (NFD instead of NFC), or /SECRETS/PASSWÖRTER.txt (different case, since default APFS volumes are case-insensitive). Other forms include ligature characters (fi vs fi, ff vs ff, …) and German ß vs ss.

The denied path and the requested path differed at the byte level, so Deno's permission check passed; the kernel then resolved them to the same inode and served the file anyway. The same flaw affected --deny-write, --deny-run, and --deny-ffi, which share the same path-comparison code.

Am I affected?

You are potentially affected if all of the following are true:

1. You run Deno on macOS (the issue is specific to APFS path-equivalence rules; Linux and Windows are not affected by this variant).
2. You rely on --deny-read, --deny-write, --deny-run, or --deny-ffi as a security boundary against less-trusted code — a dependency, plugin, or attacker-controlled input.
3. The protected path contains characters that have alternate Unicode spellings — most commonly accented characters (é, ñ, ö, …), German ß, or Latin ligatures — or you rely on case-sensitivity on a default APFS volume.

If you only run fully trusted code, or your deny rules cover paths that are pure ASCII with no case-sensitive aliases, you are not exposed to this specific bypass.

Impact

A program running with broad --allow-read (or --allow-write / --allow-run / --allow-ffi) but with --deny-* carve-outs for specific paths could read, write, execute, or load via FFI those denied paths by referring to them through a Unicode- or case-equivalent spelling. The sandbox model on macOS was weaker than the flags suggested.

Workaround

If you cannot upgrade immediately:

• Prefer --allow-* allowlists over --deny-* denylists. Allow rules match against the original specifier, so an attacker-supplied alternate spelling will not match a path you didn't explicitly grant.
• Do not rely on case-sensitivity of paths on macOS for security boundaries; default APFS volumes are case-insensitive.

Fix

On macOS, Deno now normalizes both the deny-rule path and the requested path to NFC and applies Unicode case folding before comparing them. This matches how APFS resolves paths at the inode level, so byte-different but equivalent spellings are now rejected by the same deny rule.

Summary

Deno's permission system enforces filesystem and execution restrictions by comparing the requested path against the path supplied to --deny-read, --deny-write, --deny-run, or --deny-ffi. On macOS, that comparison was done at the raw-byte level while the APFS filesystem treats different Unicode spellings of the same name as the same file.

That means a program could reach a denied path by spelling it differently than the deny rule. For example, with --deny-read=/secrets/passwörter.txt, a script could still read the file by opening /secrets/passwo\u0308rter.txt (NFD instead of NFC), or /SECRETS/PASSWÖRTER.txt (different case, since default APFS volumes are case-insensitive). Other forms include ligature characters (fi vs fi, ff vs ff, …) and German ß vs ss.

The denied path and the requested path differed at the byte level, so Deno's permission check passed; the kernel then resolved them to the same inode and served the file anyway. The same flaw affected --deny-write, --deny-run, and --deny-ffi, which share the same path-comparison code.

Am I affected?

You are potentially affected if all of the following are true:

1. You run Deno on macOS (the issue is specific to APFS path-equivalence rules; Linux and Windows are not affected by this variant).
2. You rely on --deny-read, --deny-write, --deny-run, or --deny-ffi as a security boundary against less-trusted code — a dependency, plugin, or attacker-controlled input.
3. The protected path contains characters that have alternate Unicode spellings — most commonly accented characters (é, ñ, ö, …), German ß, or Latin ligatures — or you rely on case-sensitivity on a default APFS volume.

If you only run fully trusted code, or your deny rules cover paths that are pure ASCII with no case-sensitive aliases, you are not exposed to this specific bypass.

Impact

A program running with broad --allow-read (or --allow-write / --allow-run / --allow-ffi) but with --deny-* carve-outs for specific paths could read, write, execute, or load via FFI those denied paths by referring to them through a Unicode- or case-equivalent spelling. The sandbox model on macOS was weaker than the flags suggested.

Workaround

If you cannot upgrade immediately:

• Prefer --allow-* allowlists over --deny-* denylists. Allow rules match against the original specifier, so an attacker-supplied alternate spelling will not match a path you didn't explicitly grant.
• Do not rely on case-sensitivity of paths on macOS for security boundaries; default APFS volumes are case-insensitive.

Fix

On macOS, Deno now normalizes both the deny-rule path and the requested path to NFC and applies Unicode case folding before comparing them. This matches how APFS resolves paths at the inode level, so byte-different but equivalent spellings are now rejected by the same deny rule.