feat: cap strftime pad width at 1M

docs: restructure security model with production guidance
Co-authored-by: Cursor <[email protected]>

docs/source/tutorials/options.md

@@ -140,6 +140,8 @@ It defaults to `false`. For example, when set to `true`, a blank string would ev
 
 **ownPropertyOnly** hides scope variables from prototypes, useful when you're passing a not sanitized object into LiquidJS or need to hide prototypes from templates. Defaults to `true`.
 
+Built-in DoS limits and host isolation guidance are documented in [Security Model](./security-model.html).
+
 {% note info Nonexistent Tags %}
 Nonexistent tags always throw errors during parsing and this behavior cannot be customized.
 {% endnote %}

docs/source/tutorials/security-model.md

@@ -4,20 +4,17 @@ title: Security Model
 
 LiquidJS provides DoS-oriented limits (`parseLimit`, `templateLimit`, `outputLengthLimit`, `maxDepth`) to reduce risk. This page summarizes those limits, [`ownPropertyOnly`][ownPropertyOnly], custom [`Drop`][drop] usage, and the security boundary to assume in production.
 
-## Security boundary
+## At a glance
 
-The built-in limits are cooperative safeguards, not strict runtime isolation.
+LiquidJS ships a thin cooperative DoS layer:
-
-- They do **not** equal process RSS/heap usage.
-- They do **not** sandbox JavaScript execution.
-- They should be combined with process/container limits and request timeouts for defense in depth.
-
-## Limits at a glance
 
 - [parseLimit][parseLimit]: limit total template size per `parse()` call.
 - [templateLimit][templateLimit]: limit total tag/HTML/output nodes rendered per `render()` call.
 - [outputLengthLimit][outputLengthLimit]: limit total output length per `render()` call.
 - [maxDepth][maxDepth]: limit nesting depth of `{% render %}`, `{% include %}`, and `{% layout %}`.
+- Strftime numeric pad widths in the `date` filter are capped at `1_000_000` (1M) per conversion.
+
+These are cooperative safeguards, not runtime isolation—see [Production guidance](#production-guidance) below for host-level limits and online-service hardening.
 
 ## Limit details
 
@@ -49,7 +46,7 @@ Each template node (the `for` tag, literal `order: `, output `{{i}}`, and so on)
 
 [maxDepth][maxDepth] limits how deeply `{% render %}`, `{% include %}`, and `{% layout %}` can nest. Defaults to `128`. In sync rendering (`renderSync`), nested tags are driven by `toValueSync`, which recursively resumes each yielded generator on the call stack—deep nesting can overflow it, and `maxDepth` caps that depth. Async `render()` resumes the same tag generators via `toPromise`/`yield` without a deep synchronous call chain, so stack overflow is not a concern there (the limit still applies as a DoS guard).
 
-The `memoryLimit` option was removed; memory usage is not capped in-engine.
+The `memoryLimit` option was removed in v11; enforce memory limits at the host or process level instead.
 
 ## `ownPropertyOnly` and scope data
 
@@ -59,15 +56,22 @@ With [`ownPropertyOnly`][ownPropertyOnly] `true`, plain scope objects only expos
 
 [`Drop`][drop] values are not restricted the same way: LiquidJS still reads the prototype chain and may call [`liquidMethodMissing`][liquidMethodMissing]. **You** control what a drop exposes; narrow APIs and never feed unsafe data into drops unless the class is built for template access. `ownPropertyOnly` alone does not harden custom drops—audit them like any privileged code.
 
-## Online service guidance
+## Production guidance
 
-If you run an online service, avoid rendering fully user-defined templates whenever possible.
+LiquidJS does not sandbox template code—custom filters, tags, and scope helpers run as ordinary JavaScript with your process privileges. For production with untrusted templates, treat built-in DoS limits as one layer in a broader strategy.
 
-- Prefer curated templates or a restricted template subset.
+Host-level defenses:
-- If user-defined templates are required, isolate rendering (worker/process/container), enforce OS/container memory and CPU limits, and apply request rate limits.
-- Treat `parseLimit`, `templateLimit`, `outputLengthLimit`, and `maxDepth` as one layer in a broader DoS defense strategy.
 
-For heavy single-template operations, process-level isolation is still recommended (for example with [paralleljs][paralleljs]).
+- Run each render in a **worker thread or child process** with a wall-clock timeout; **kill** the worker on expiry.
+- Enforce **container/Kubernetes cgroup limits**, `ulimit`, or equivalent on the renderer process for memory and CPU.
+- Apply **request rate limits** at the API or gateway layer.
+- **`node:vm` and `isolated-vm` are not a security boundary** for LiquidJS: custom filters and tags run ordinary host JavaScript with your privileges.
+- Unlike Jinja/Twig sandbox modes, LiquidJS has **no restricted interpreter**—template logic executes in the same JS runtime as your app.
+
+For online services that accept template input:
+
+- Avoid rendering fully user-defined templates whenever possible; prefer curated templates or a restricted template subset.
+- For heavy single-template operations, process-level isolation is still recommended (for example with [paralleljs][paralleljs]).
 
 [paralleljs]: https://www.npmjs.com/package/paralleljs
 [parseLimit]: /api/interfaces/LiquidOptions.html#parseLimit

src/util/strftime.spec.ts

@@ -188,6 +188,14 @@ describe('util/strftime', function () {
     it('should have higher priority than H', () => {
       expect(t(then, '%0H')).toBe('03')
     })
+    it('should allow pad width up to MAX_STRFTIME_PAD', () => {
+      expect(t(now, '%100000d').length).toBe(100000)
+      expect(t(now, `%${1_000_000}d`).length).toBe(1_000_000)
+    })
+    it('should throw when pad width exceeds MAX_STRFTIME_PAD', () => {
+      expect(() => t(now, `%${1024 * 1024 + 1}d`)).toThrow('strftime pad width limit exceeded')
+      expect(() => t(now, '%5000000d')).toThrow('strftime pad width limit exceeded')
+    })
   })
   describe('modifier field', () => {
     it('should ignore E modifier', () => {

src/util/strftime.ts

@@ -1,5 +1,9 @@
 import { changeCase, padStart, padEnd } from './underscore'
 import { LiquidDate } from './liquid-date'
+import { assert } from './assert'
+
+/** Per-conversion numeric width cap for strftime (%N, %15d, …). */
+export const MAX_STRFTIME_PAD = 1024 * 1024
 
 const rFormat = /%([-_0^#:]+)?(\d+)?([EO])?(.)/
 interface FormatOptions {
@@ -96,6 +100,7 @@ const formatCodes: Record<string, FormatCodeHandler> = {
   M: (d: LiquidDate) => d.getMinutes(),
   N: (d: LiquidDate, opts: FormatOptions) => {
     const width = Number(opts.width) || 9
+    assertPadWidth(width)
     const str = String(d.getMilliseconds()).slice(0, width)
     return padEnd(str, width, '0')
   },
@@ -132,6 +137,10 @@ export function strftime (d: LiquidDate, formatStr: string) {
   return output + remaining
 }
 
+function assertPadWidth (width: number) {
+  assert(width <= MAX_STRFTIME_PAD, 'strftime pad width limit exceeded')
+}
+
 function format (d: LiquidDate, match: RegExpExecArray) {
   const [input, flagStr = '', width, modifier, conversion] = match
   const convert = formatCodes[conversion]
@@ -146,5 +155,6 @@ function format (d: LiquidDate, match: RegExpExecArray) {
   if (flags['_']) padChar = ' '
   else if (flags['0']) padChar = '0'
   if (flags['-']) padWidth = 0
+  else assertPadWidth(padWidth)
   return padStart(ret, padWidth, padChar)
 }

test/integration/filters/date.spec.ts

@@ -210,6 +210,16 @@ describe('filters/date', function () {
       const out = liquid.parseAndRenderSync('{{ d | date: f }}', { d: 'now', f: '%5000d' })
       expect(out.length).toBe(5000)
     })
+    it('should honor large numeric strftime pad width up to the cap', () => {
+      const liquid = new Liquid()
+      const out = liquid.parseAndRenderSync('{{ d | date: f }}', { d: 'now', f: '%100000d' })
+      expect(out.length).toBe(100000)
+    })
+    it('should throw when numeric strftime pad width is too large', () => {
+      const liquid = new Liquid()
+      expect(() => liquid.parseAndRenderSync('{{ d | date: f }}', { d: 'now', f: '%5000000d' }))
+        .toThrow('strftime pad width limit exceeded')
+    })
   })
 })
 describe('filters/date_to_xmlschema', function () {