2nd/10_Wiki/Topics/Architecture/배수구(Sinks).md

---
id: wiki-2026-0508-배수구-sinks
title: 배수구 (Sinks)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Sinks, Taint Sinks, Dangerous Sinks, Vulnerable Functions]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [security, taint-analysis, sast, vulnerabilities, appsec]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: multi
  framework: Semgrep/CodeQL
---

# 배수구 (Sinks)

## 매 한 줄
> **"매 untrusted data 의 dangerous 의 reach 한 곳 — 매 taint analysis 의 endpoint."**. Source (사용자 input) → Flow (변수, 함수 chain) → Sink (eval, exec, SQL, file write). 2026 SAST tooling (CodeQL, Semgrep, Snyk Code) 은 매 이 source-to-sink graph 의 trace — 매 sanitizer 의 absence 의 vulnerability 의 flag.

## 매 핵심

### 매 sink 의 종류
- **Code execution**: `eval`, `exec`, `Function()`, `os.system`, 매 deserialize.
- **SQL**: 매 raw query string concat (`f"SELECT * FROM u WHERE id={id}"`).
- **Command**: `subprocess.Popen(shell=True)`, `child_process.exec`.
- **Path**: `open(path)` with 매 user-controlled path → traversal.
- **HTML/DOM**: `innerHTML`, `document.write` → XSS.
- **SSRF**: `requests.get(user_url)` → 매 internal network access.
- **Log forging / template**: 매 user input 의 unescape 된 template.

### 매 source 의 종류
- HTTP request body/query/header.
- 매 file content (untrusted upload).
- 매 environment variable (in shared env).
- 매 third-party API response.
- 매 message queue payload.

### 매 응용
1. 매 SAST rule 의 author — 매 custom sink 의 register.
2. 매 code review 의 checklist — 매 sink 의 list 의 grep.
3. 매 fuzzing target 의 prioritize — 매 sink 가 most 인 endpoint.

## 💻 패턴

### Semgrep — custom sink rule
```yaml
rules:
  - id: python-eval-tainted
    pattern-sources:
      - pattern: request.$X
    pattern-sinks:
      - pattern: eval(...)
      - pattern: exec(...)
    pattern-sanitizers:
      - pattern: ast.literal_eval(...)
    message: User input 의 eval 의 reach
    severity: ERROR
    languages: [python]
```

### CodeQL — taint tracking
```ql
import python
import semmle.python.dataflow.new.TaintTracking

class UserInputToSqlConfig extends TaintTracking::Configuration {
  override predicate isSource(DataFlow::Node n) {
    n.asExpr().(Attribute).getAttr() in ["args", "form", "json"]
  }
  override predicate isSink(DataFlow::Node n) {
    exists(Call c | c.getFunc().(Attribute).getAttr() = "execute" |
      n.asExpr() = c.getArg(0))
  }
}
```

### SQL sink — parameterize (fix)
```python
# BAD — sink reachable
db.execute(f"SELECT * FROM users WHERE id = {user_id}")

# GOOD — sink 의 sanitize (parameterized)
db.execute("SELECT * FROM users WHERE id = %s", (user_id,))
```

### Command sink — avoid shell
```python
# BAD
subprocess.run(f"ping {host}", shell=True)

# GOOD
subprocess.run(["ping", "-c", "1", host], shell=False)
```

### Path traversal sink — resolve + check
```python
import os
base = "/var/uploads"
path = os.path.realpath(os.path.join(base, user_filename))
if not path.startswith(base + os.sep):
    raise PermissionError("path traversal")
open(path, "rb")
```

### XSS sink — escape
```javascript
// BAD
el.innerHTML = userBio;

// GOOD — DOM API
el.textContent = userBio;
// 또는 매 DOMPurify 의 sanitize 후
el.innerHTML = DOMPurify.sanitize(userBio);
```

### SSRF — allowlist
```python
from urllib.parse import urlparse
ALLOWED_HOSTS = {"api.partner.com", "img.cdn.com"}
def safe_fetch(url):
    host = urlparse(url).hostname
    if host not in ALLOWED_HOSTS: raise ValueError("blocked host")
    # 매 DNS rebinding 의 also guard — 매 resolve + IP check
    return requests.get(url, timeout=5)
```

### Deserialize sink — never on untrusted
```python
# BAD — pickle 의 RCE
data = pickle.loads(request.body)

# GOOD — JSON only
data = json.loads(request.body)
```

## 매 결정 기준
| Sink type | Sanitizer | Notes |
|---|---|---|
| SQL | Parameterized query, ORM | 매 string concat 의 X |
| Shell | argv list, no `shell=True` | 매 quoting 의 trust 의 X |
| Path | realpath + prefix check | symlink 의 also handle |
| HTML | textContent or DOMPurify | 매 innerHTML 매 last resort |
| Eval | 매 그냥 사용 X | 매 alternative 의 find |
| Deserialize | JSON only on untrusted | pickle/yaml.load 매 X |

**기본값**: 매 sink 의 see 한 후 매 source 의 trace — 매 sanitizer 의 between 의 verify.

## 🔗 Graph
- 부모: [[Application_Security]] · [[Taint_Analysis]]
- 변형: [[SAST]] · [[DAST]] · [[IAST]]
- 응용: [[OWASP_Top_10]] · [[Code_Injection]] · [[XSS]] · [[SQL_Injection]]
- Adjacent: [[Sources]] · [[Sanitizers]] · [[Fuzzing]]

## 🤖 LLM 활용
**언제**: 매 unfamiliar codebase 의 sink inventory 의 quickly 의 generate, 매 PR 매 new sink 의 introduce 의 spot.
**언제 X**: 매 production-grade SAST 의 replace — 매 LLM 의 false negative 의 risk, 매 dedicated tooling 의 use.

## ❌ 안티패턴
- **Blacklist sanitizer**: 매 known-bad 의 remove — 매 bypass 의 always exist.
- **Sanitize at sink**: 매 throughout flow 의 mutate — 매 single point 의 trust 의 X.
- **Trust 매 internal**: 매 internal API 의 source 의 also treat — 매 SSRF · Confused deputy.
- **Generic exception**: 매 sanitizer fail 의 silent swallow — 매 fail closed.
- **String comparison 의 host check**: 매 `endswith("trusted.com")` → `evil-trusted.com` bypass.

## 🧪 검증 / 중복
- Verified (OWASP Source-Sink-Sanitizer model, CodeQL taint tracking docs, Semgrep registry 2026).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — sink categories, SAST rules, sanitizer patterns |