MEDIUM 5.9 Microsoft

CVE-2026-21717

A flaw in V8's string hashing mechanism causes integer-like strings to be hashed to their numeric value, making hash collisions trivially predictable. By crafting a request that causes many such collisions in V8's internal string table, an attacker can significantly degrade performance of the Node.js process. The most common trigger is any endpoint that calls `JSON.parse()` on attacker-controlled input, as JSON parsing automatically internalizes short strings into the affected hash table. This vulnerability affects **20.x, 22.x, 24.x, and 25.x**.

Microsoft Security Update 2026-Aug: A flaw in V8's string hashing mechanism causes integer-like strings to be hashed to their numeric value, making hash collisions trivially predictable. By crafting a request that causes many such collisions in V8's internal string table, an attacker can significantly degrade performance of the Node.js process. The most common trigger is any endpoint that calls `JSON.parse()` on attacker-controlled input, as JSON parsing automatically internalizes short strings into the affected hash table. This vulnerability affects **20.x, 22.x, 24.x, and 25.x**.

Affected Products

References

Published: 2026-08-06 · Source: Microsoft · Feed updated: 2026-08-10
This medium severity vulnerability with a CVSS score of 5.9 was published on 2026-08-06 via Microsoft. Affected: azl3 nodejs 20.14.0-15 on Azure Linux 3.0, cbl2 nodejs18 18.20.3-12 on CBL Mariner 2.0, azl3 nodejs 20.14.0-14 on Azure Linux 3.0 and 2 more.
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