LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to version 10.25.1, LiquidJS's `memoryLimit` security mechanism can be completely bypassed by using reverse range expressions (e.g., `(100000000..1)`), allowing an attacker to allocate unlimited memory. Combined with a string flattening operation (e.g., `replace` filter), this causes a V8 Fatal error that crashes the Node.js process, resulting in complete denial of service from a single HTTP request. Version 10.25.1 patches the issue.

Affected: npm: liquidjs

### Summary

LiquidJS's `memoryLimit` security mechanism can be completely bypassed by using reverse range expressions (e.g., `(100000000..1)`), allowing an attacker to allocate unlimited memory. Combined with a string flattening operation (e.g., `replace` filter), this causes a **V8 Fatal error that crashes the Node.js process**, resulting in complete denial of service from a single HTTP request.

### Details When LiquidJS evaluates a range token `(low..high)`, it calls `ctx.memoryLimit.use(high - low + 1)` in `src/render/expression.ts:70` to account for memory usage. However, for reverse ranges where `low > high` (e.g., `(100000000..1)`), this computation yields a negative value (`1 - 100000000 + 1 = -99999998`).

The `Limiter.use()` method in `src/util/limiter.ts:11-14` does not validate that the `count` parameter is non-negative. It simply adds `count` to `this.base`, causing the internal counter to go negative. Once the counter is sufficiently negative, subsequent legitimate memory allocations that would normally exceed the configured `memoryLimit` pass the `base + count <= limit` assertion.

```typescript // src/render/expression.ts:67-72 function * evalRangeToken (token: RangeToken, ctx: Context) { const low: number = yield evalToken(token.lhs, ctx) const high: number = yield evalToken(token.rhs, ctx) ctx.memoryLimit.use(high - low + 1) // high=1, low=1e8 → use(-99999999) return range(+low, +high + 1) }

// src/util/limiter.ts:11-14 use (count: number) { co…