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**.

CVE-2026-21717 is fixed in 46 products on 2 platforms, first by RHSA-2026:7670, released March 12, 2026. 12 other affected products have no fix yet. It is not reported as exploited. Patch Radar priority: High.