CVE-2026-49401

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.

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.

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.

CVE-2026-49401 has a CVSS score of 5.2 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.7.14); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2026-49401? CVE-2026-49401 is a medium-severity security vulnerability in deno (rust), affecting versions <= 2.7.13. It is fixed in 2.7.14.
2. How severe is CVE-2026-49401? CVE-2026-49401 has a CVSS score of 5.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of deno are affected by CVE-2026-49401? deno (rust) versions <= 2.7.13 is affected.
4. Is there a fix for CVE-2026-49401? Yes. CVE-2026-49401 is fixed in 2.7.14. Upgrade to this version or later.
5. Is CVE-2026-49401 exploitable, and should I be worried? Whether CVE-2026-49401 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-49401 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-49401? Upgrade deno to 2.7.14 or later.