Medium

Node.js denial of service via malformed IDN in url.format()

IdentifiersCVE-2026-21712CWE-617

CVE-2026-21712 is a medium-severity denial-of-service vulnerability in Node.js URL handling affecting the 24.x and 25.x release lines. A malformed internationalized domain name (IDN) containing invalid characters, when passed to url.format(), can trigger an assertion failure in native code within node_url.cc. Because the failure occurs as a native assertion rather than a recoverable JavaScript exception, the Node.js process terminates. The issue is specifically tied to malformed IDN processing during URL formatting.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation causes the Node.js process to crash, resulting in denial of service. There is no indication in the provided content of code execution, privilege escalation, or data disclosure; the documented impact is process termination and service interruption.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by preventing untrusted or attacker-controlled malformed internationalized domain names from reaching url.format(). Validate and sanitize hostname/URL inputs before formatting, especially where user-supplied domain names are processed. Because the fault is a native assertion crash, application-level exception handling should not be relied upon as an effective mitigation.

Remediation

Patch, then assume compromise.

Upgrade Node.js to a patched release. The provided content states that Node.js addressed this issue in the March 2026 security releases, including Node.js v24.14.1 and v25.8.2. Use the vendor-fixed release appropriate for the deployed major version.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

NodejsNodejsapplication

Rocky LinuxNodejs24application

Rocky LinuxRocky Linuxoperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

5 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

5 SOURCESView more in app

thecyberexpress com vulnerabilitiesNews

Mar 26, 2026

Node.js Fixes CVE-2026-21637 And Critical Flaws Now

A Node.js vulnerability where a malformed internationalized domain name passed to url.format() can trigger an assertion failure and crash the process.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1