LiquidJS has Exponential Memory Amplification through its replace_first Filter $& Pattern

• < 10.25.1

### Summary The `replace_first` filter in LiquidJS uses JavaScript's `String.prototype.replace()` which interprets `$&` as a backreference to the matched substring. The filter only charges `memoryLimit` for the input string length, not the amplified output. An attacker can achieve exponential memory amplification (up to 625,000:1) while staying within the `memoryLimit` budget, leading to denial of service. ### Details The `replace_first` filter in `src/builtin/filters/string.ts:130-133` delegates to JavaScript's native `String.prototype.replace()`. This native method interprets special replacement patterns including `$&` (insert the matched substring), `$'` (insert the portion after the match), and `` $` `` (insert the portion before the match). The filter calls `memoryLimit.use(str.length)` to account for the **input** string's memory cost, but the **output** string — potentially many times larger due to `$&` expansion — is never charged against the memory limit. An attacker can build a 1MB string (within `memoryLimit` budget), then use `replace_first` with a replacement string containing 50 repetitions of `$&`. Each `$&` expands to the full matched string (1MB), producing a 50

GitHub Advisory Database

• SEMVER: introduced 0; fixed 10.25.1

### Summary The `replace_first` filter in LiquidJS uses JavaScript's `String.prototype.replace()` which interprets `$&` as a backreference to the matched substring. The filter only charges `memoryLimit` for the input string length, not the amplified output. An attacker can achieve exponential memory amplification (up to 625,000:1) while staying within the `memoryLimit` budget, leading to denial of service. ### Details The `replace_first` filter in `src/builtin/filters/string.ts:130-133` delegates to JavaScript's native `String.prototype.replace()`. This native method interprets special replacement patterns including `$&` (insert the matched substring), `$'` (insert the portion after the match), and `` $` `` (insert the portion before the match). The filter calls `memoryLimit.use(str.length)` to account for the **input** string's memory cost, but the **output** string — potentially many times larger due to `$&` expansion — is never charged against the memory limit. An attacker can build a 1MB string (within `memoryLimit` budget), then use `replace_first` with a replacement string containing 50 repetitions of `$&`. Each `$&` expands to the full matched string (1MB), producing a 50

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