CVE-2026-49440 Deno: Miller-Rabin Primality Test Allows Zero Rounds

What is CVE-2026-49440?

CVE-2026-49440 is a high-severity vulnerability in denoland deno, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, node:crypto.checkPrime(candidate[, options][, callback]) and crypto.checkPrimeSync(candidate[, options]) ran no Miller-Rabin rounds at all when the caller left options.checks at its default of 0. In that mode, the only test applied to the candidate was trial division by the primes up to 17,863. Any composite whose smallest prime factor exceeds that bound — for example the product of two primes just above it, such as 17,881 × 17,891 — was reported as true ("probably prime"). The same divergence affected the lower-level op_node_check_prime / op_node_check_prime_bytes paths that the polyfill calls into. This vulnerability is fixed in 2.8.1.

Weakness: CWE-325

Which versions are affected by CVE-2026-49440?

2 open source packages ship an affected version, including deno. It affects 1 product.

Products include Deno Deno.

How do I fix CVE-2026-49440?

Upgrade deno to 2.8.1 or later.

Is CVE-2026-49440 being exploited?

There is no known exploitation of CVE-2026-49440 in the wild and no public exploit code.

Other vulnerabilities in denoland deno

• CVE-2023-28445 Deno improperly handles resizable ArrayBuffer Critical 10.0
• CVE-2022-24783 Sandbox bypass leading to arbitrary code execution in Deno Critical 10.0
• CVE-2021-32619 Static imports inside dynamically imported modules do not adhere to permission checks Critical 9.8
• CVE-2026-22863 Deno node:crypto doesn't finalize cipher Critical 9.2
• CVE-2024-27936 Deno interactive permission prompt spoofing via improper ANSI stripping High 8.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-9xg4-qhm4-g43w, JLSEC-2026-658.