CVE-2026-49440

CVE-2026-49440 is a high-severity vulnerability in Deno with a CVSS 3.x base score of 7.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-325.

Key facts

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.

Frequently asked questions

What is CVE-2026-49440?
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.
How severe is CVE-2026-49440?
CVE-2026-49440 has a CVSS 3.x base score of 7.4, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-49440 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (5th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-49440?
CVE-2026-49440 affects Deno. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-49440?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-49440 have an EU (EUVD) identifier?
Yes. CVE-2026-49440 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38540.
When was CVE-2026-49440 published?
CVE-2026-49440 was published on 2026-06-23 and last updated on 2026-06-26.

References

Affected products (1)

More vulnerabilities in Deno

All CVEs affecting Deno →

Other CWE-325 vulnerabilities

Browse all CWE-325 vulnerabilities →