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High

HashDoS in Node.js v24.x via V8 rapidhash string hashing

IdentifiersCVE-2025-27209CWE-400

CVE-2025-27209 is a hash-collision denial-of-service vulnerability affecting Node.js v24.x, specifically reported as impacting Node.js v24.0.0 through v24.4.0. The issue was introduced by the V8 release shipped with Node.js v24.0.0, which changed string hash computation to use rapidhash. According to the provided content, the rapidhash implementation reintroduced a HashDoS condition because attackers who can control strings being hashed can generate large numbers of collisions even without knowing the hash seed. The root cause is described as insufficient randomness/collision resistance and a configuration gap that left rapidhash constants hard-coded without effective seeding. In vulnerable applications, attacker-supplied strings used as keys in JavaScript hash-based structures such as objects and Maps can trigger pathological collision behavior, degrading normal average-case hash-table performance into worst-case behavior and enabling denial of service.

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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 can cause severe performance degradation and denial of service in Node.js applications. By supplying crafted colliding strings, a remote attacker can force operations on JavaScript objects and Maps from expected average O(1) behavior to worst-case O(n), driving excessive CPU consumption and potentially causing service slowdown, request starvation, or process instability/crash. The issue is particularly relevant to public-facing services that ingest attacker-controlled strings through common inputs such as HTTP headers, query parameters, or JSON keys.

Mitigation

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

If immediate upgrade is not possible, reduce exposure by limiting or sanitizing attacker-controlled strings before they are used as keys in hash-based data structures, especially for public-facing request components such as HTTP headers, query parameters, and JSON object keys. Enforce strict input size and cardinality limits, reject unusually large numbers of distinct keys, apply request rate limiting, and monitor for abnormal CPU spikes or requests containing high volumes of crafted key material. These measures may reduce exploitability but do not replace upgrading to a fixed Node.js release.

Remediation

Patch, then assume compromise.

Upgrade Node.js to v24.4.1 or later. The provided content states that Node.js addressed the issue in its July 2025 security release by shipping Node.js v24.4.1 with an updated V8 engine and a revised, more secure string hashing mechanism replacing the vulnerable rapidhash behavior. Versions earlier than v24.0.0 are described as not vulnerable, and v24.4.1 onward are described as fixed.
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.

ACTIVITY FEED

Recent activity

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

9 SOURCESView more in app
What this page doesn’t show

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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 activity7

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2025-27209
NVD
nvd.nist.gov/vuln/detail/CVE-2025-27209
MITRE CWE · CWE-400
cwe.mitre.org
openwall.com
openwall.com/lists/oss-security/2025/07/22/2
nodejs.org
nodejs.org/en/blog/vulnerability/july-2025-security-releases