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CVE-2026-49440 high CVSS 7.4

Vulnerability in deno (CVE-2026-49440)

Summary

Vulnerability in deno (CVE-2026-49440). Confidential information can be exposed externally. Exploitable via options.checks. Mitigation: upgrade to 2.8.1 or later.

Original description

The description as published by the source.

Summary

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.

Node.js itself does not have this problem: it forwards checks = 0 to OpenSSL's BN_check_prime, which substitutes a sensible default number of rounds based on the candidate's bit length (per FIPS 186-4 Appendix C.3 Table C.1). Deno's Rust implementation had no equivalent fallback, so count = 0 meant "skip the loop entirely."

Affected APIs

  • crypto.checkPrime(candidate) (callback form, default options)
  • crypto.checkPrime(candidate, { checks: 0 }, callback)
  • crypto.checkPrimeSync(candidate) (default options)
  • crypto.checkPrimeSync(candidate, { checks: 0 })

Callers who explicitly passed checks >= 1 were less affected, the loop ran the number of rounds they asked for, but were still receiving fewer rounds than Node would have applied for the same bit length. With the patched version they get at least the FIPS minimum.

Not af…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-49440 has been found in deno.
Attackers can target a specific entry point like options.checks over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade deno to 2.8.1 or later.
If unsure, ask your IT team or search "deno CVE-2026-49440" on the vendor's site.

CVE-2026-49440 (deno) — CWE-325 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: options.checks / true / op_node_check_prime / op_node_check_prime_bytes
Patched: 2.8.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-325) exists in deno. Attackers reach the vulnerable code path via options.checks without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of deno. Attack surface: options.checks / true / op_node_check_prime / op_node_check_prime_bytes.

🔥 Severity

Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 2.8.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'deno' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'deno' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で deno を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade deno to 2.8.1

    ステージング環境で 2.8.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

rust deno
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.1"}]}]
crates.io deno
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.8.1"}]}]

References

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