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

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

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

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

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)

# 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

# BAD
subprocess.run(f"ping {host}", shell=True)

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

Path traversal sink — resolve + check

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

// BAD
el.innerHTML = userBio;

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

SSRF — allowlist

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

# 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
• 변형: SAST · 보안 및 시스템 신뢰성 표준 · IAST
• 응용: OWASP Top 10
• Adjacent: 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