LiquidJS is a Shopify / GitHub Pages compatible template engine in pure JavaScript. Prior to 10.25.3, the replace filter in LiquidJS incorrectly accounts for memory usage when the memoryLimit option is enabled. It charges str.length + pattern.length + replacement.length bytes to the memory limiter, but the actual output from str.split(pattern).join(replacement) can be quadratically larger when the pattern occurs many times in the input string. This allows an attacker who controls template content to bypass the memoryLimit DoS protection with approximately 2,500x amplification, potentially causing out-of-memory conditions. This vulnerability is fixed in 10.25.3.

Affected: npm: liquidjs

## Summary

The `replace` filter in LiquidJS incorrectly accounts for memory usage when the `memoryLimit` option is enabled. It charges `str.length + pattern.length + replacement.length` bytes to the memory limiter, but the actual output from `str.split(pattern).join(replacement)` can be quadratically larger when the pattern occurs many times in the input string. This allows an attacker who controls template content to bypass the `memoryLimit` DoS protection with approximately 2,500x amplification, potentially causing out-of-memory conditions.

## Details

The vulnerable code is in `src/filters/string.ts:137-142`:

```typescript export function replace (this: FilterImpl, v: string, pattern: string, replacement: string) { const str = stringify(v) pattern = stringify(pattern) replacement = stringify(replacement) this.context.memoryLimit.use(str.length + pattern.length + replacement.length) // BUG: accounts for inputs, not output return str.split(pattern).join(replacement) // actual output can be quadratically larger } ```

The `memoryLimit.use()` call charges only the sum of the three input lengths. However, the `str.split(pattern).join(replacement)` operation produces output of size:

``` (number_of_occurrences * replacement.length) + non_matching_characters ```

When every character in `str` matches `pattern` (e.g., `str` = 5,000 `a`s, `pattern` = `a`), there are 5,000 occurrences. With a 5,000-character replacement string, the output is `5000 * 5000 = 25,000,000…