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csp_scanner.py — Content Security Policy (CSP) Deep Auditor
============================================================
Parses and analyses the Content-Security-Policy (and CSP-Report-Only) header:
- Detects missing CSP entirely
- Flags unsafe-inline / unsafe-eval in script-src
- Flags wildcard (*) sources
- Detects missing critical directives
- Identifies CSP bypass vectors (data:, blob:, http: schemes)
- Checks for report-uri / report-to configuration
- Scores overall CSP strength
"""
import re
import urllib.request
import urllib.error
from scanners.base_scanner import BaseScanner
CRITICAL_DIRECTIVES = [
"default-src", "script-src", "style-src", "img-src",
"connect-src", "font-src", "object-src", "frame-ancestors",
]
BYPASS_SCHEMES = ["data:", "blob:", "http:", "javascript:"]
CDNS_ALLOWLISTED_BUT_RISKY = [
"cdn.jsdelivr.net", "unpkg.com", "cdnjs.cloudflare.com",
"ajax.googleapis.com", "code.jquery.com",
]
class CspScanner(BaseScanner):
SCANNER_NAME = "Content Security Policy (CSP) Auditor"
_SCANNER_KEY = "csp"
def __init__(self, scan_id, target, domain, **kwargs):
super().__init__(scan_id, target, domain, **kwargs)
def run(self) -> list:
self.log("INFO", f"[CSP] Auditing Content-Security-Policy on {self.target}...")
try:
headers = self._fetch_headers()
csp = headers.get("content-security-policy", "")
csp_ro = headers.get("content-security-policy-report-only", "")
if not csp and not csp_ro:
self.log("WARNING", "[CSP] No Content-Security-Policy header found!")
self.add_vuln(
title="Content Security Policy (CSP) Not Configured",
severity="High",
category="Content Security Policy",
cvss_score=7.5,
description=f"The target `{self.target}` does not serve a "
"Content-Security-Policy header. Without CSP, the browser has "
"no policy to enforce, making XSS attacks significantly more "
"damaging as injected scripts run with full page privileges.",
remediation="Implement a strict CSP:\n"
"Content-Security-Policy: default-src 'self'; "
"script-src 'self' 'nonce-{random}'; "
"object-src 'none'; base-uri 'self'; frame-ancestors 'none'",
evidence="No Content-Security-Policy header in response",
request_details=f"GET {self.target}",
response_details="Missing Content-Security-Policy header",
confidence="Confirmed",
)
return self.vulns
active_csp = csp or csp_ro
label = "CSP-Report-Only" if not csp else "CSP"
self.log("INFO", f"[CSP] {label} header found. Parsing directives...")
if not csp and csp_ro:
self.add_vuln(
title="CSP Deployed in Report-Only Mode (Not Enforced)",
severity="Medium",
category="Content Security Policy",
cvss_score=5.3,
description="A Content-Security-Policy-Report-Only header is present but "
"no enforcing CSP header exists. Report-Only mode does not prevent "
"attacks — it only sends violation reports.",
remediation="Promote the policy to Content-Security-Policy once verified.",
evidence="Content-Security-Policy-Report-Only present, no enforcing CSP",
request_details=f"GET {self.target}",
response_details="Report-Only mode CSP detected",
confidence="High",
)
directives = self._parse_csp(active_csp)
self._audit_directives(directives, active_csp)
except Exception as e:
self.log("ERROR", f"[CSP] Audit error: {e}")
self.log(
"SUCCESS" if not self.vulns else "WARNING",
f"[CSP] Audit complete. {len(self.vulns)} issue(s) found.",
)
return self.vulns
def _fetch_headers(self) -> dict:
body, status, resp_headers = self._make_request(
self.target, return_response_obj=True
)
if resp_headers:
return {k.lower(): v for k, v in resp_headers.items()}
return {}
@staticmethod
def _parse_csp(csp: str) -> dict:
directives = {}
for part in csp.split(";"):
part = part.strip()
if not part:
continue
tokens = part.split()
if tokens:
directives[tokens[0].lower()] = tokens[1:]
return directives
def _audit_directives(self, directives: dict, raw_csp: str):
script_src = directives.get("script-src",
directives.get("default-src", []))
if "'unsafe-inline'" in script_src:
self.add_vuln(
title="CSP Allows 'unsafe-inline' in script-src",
severity="High",
category="Content Security Policy",
cvss_score=7.4,
description="The CSP `script-src` directive includes `'unsafe-inline'`, "
"which allows inline `<script>` blocks and `onclick=` handlers. "
"This completely undermines XSS protection provided by CSP.",
remediation="Replace 'unsafe-inline' with nonce-based or hash-based "
"script allowlisting:\n"
"script-src 'self' 'nonce-{server_generated_random}';",
evidence=f"script-src contains 'unsafe-inline': {script_src}",
payload="'unsafe-inline' in CSP",
request_details=f"GET {self.target}",
response_details=f"CSP directives: {directives}",
confidence="Confirmed",
)
else:
self.log("SUCCESS", "[CSP] 'unsafe-inline' not found in script-src")
if "'unsafe-eval'" in script_src:
self.add_vuln(
title="CSP Allows 'unsafe-eval' in script-src",
severity="Medium",
category="Content Security Policy",
cvss_score=5.3,
description="The CSP `script-src` allows `eval()`, `new Function()`, "
"and similar dynamic code execution. This weakens XSS mitigation.",
remediation="Remove 'unsafe-eval'. Refactor code to avoid eval(). "
"Use JSON.parse() instead of eval() for JSON data.",
evidence=f"script-src contains 'unsafe-eval': {script_src}",
payload="'unsafe-eval' in CSP",
request_details=f"GET {self.target}",
response_details=f"CSP directives: {directives}",
confidence="Confirmed",
)
for directive, sources in directives.items():
if "*" in sources:
self.add_vuln(
title=f"CSP Wildcard (*) Source in '{directive}'",
severity="High",
category="Content Security Policy",
cvss_score=7.5,
description=f"The `{directive}` directive allows any origin (`*`), "
"effectively disabling the protection for this resource type.",
remediation=f"Replace `*` in `{directive}` with explicit, "
"trusted origins only.",
evidence=f"{directive}: {' '.join(sources)} contains wildcard",
payload=f"{directive} *",
request_details=f"GET {self.target}",
response_details=f"CSP directive {directive} allows *",
confidence="Confirmed",
)
for scheme in BYPASS_SCHEMES:
if scheme in raw_csp:
self.add_vuln(
title=f"CSP Bypass via '{scheme}' Scheme Allowed",
severity="Medium",
category="Content Security Policy",
cvss_score=5.5,
description=f"The CSP permits the `{scheme}` scheme, which is commonly "
"abused for CSP bypass techniques (especially data: URIs for script execution).",
remediation=f"Remove `{scheme}` from all CSP directives unless strictly required.",
evidence=f"CSP contains bypass scheme: {scheme}",
payload=f"{scheme} in CSP",
request_details=f"GET {self.target}",
response_details=f"CSP allows scheme: {scheme}",
confidence="High",
)
obj_src = directives.get("object-src", directives.get("default-src", []))
if not obj_src or (obj_src != ["'none'"] and "'none'" not in obj_src):
self.add_vuln(
title="CSP Missing 'object-src none' Directive",
severity="Medium",
category="Content Security Policy",
cvss_score=5.3,
description="Without `object-src 'none'`, the browser may load Flash, "
"Java applets, or other plugins that bypass script-src restrictions.",
remediation="Add: object-src 'none'; to your CSP.",
evidence=f"object-src directive: {obj_src}",
request_details=f"GET {self.target}",
response_details="object-src not set to 'none'",
confidence="High",
)
if "frame-ancestors" not in directives:
self.add_vuln(
title="CSP Missing 'frame-ancestors' Directive (Clickjacking)",
severity="Medium",
category="Content Security Policy",
cvss_score=5.4,
description="The CSP does not include `frame-ancestors`, which controls "
"whether the page can be embedded in iframes. Without it, clickjacking "
"attacks remain possible if X-Frame-Options is also absent.",
remediation="Add: frame-ancestors 'none'; (or 'self' if same-origin framing needed)",
evidence="Directives present: " + ", ".join(directives.keys()),
request_details=f"GET {self.target}",
response_details="frame-ancestors directive missing",
confidence="High",
)
else:
self.log("SUCCESS", "[CSP] frame-ancestors directive present")
if "base-uri" not in directives:
self.add_vuln(
title="CSP Missing 'base-uri' Directive",
severity="Low",
category="Content Security Policy",
cvss_score=3.5,
description="Without `base-uri`, an attacker who injects a `<base>` tag "
"can redirect all relative URLs to an attacker-controlled origin.",
remediation="Add: base-uri 'self'; to your CSP.",
evidence="Directives present: " + ", ".join(directives.keys()),
request_details=f"GET {self.target}",
response_details="base-uri directive missing",
confidence="High",
)
if "report-uri" not in directives and "report-to" not in directives:
self.add_vuln(
title="CSP Has No Reporting Endpoint Configured",
severity="Low",
category="Content Security Policy",
cvss_score=2.0,
description="The CSP does not include a `report-uri` or `report-to` "
"directive. Without reporting, CSP violations go undetected.",
remediation="Add: report-uri /csp-report-endpoint; "
"to receive violation reports from browsers.",
evidence="Directives present: " + ", ".join(directives.keys()),
request_details=f"GET {self.target}",
response_details="No report-uri or report-to directive",
confidence="High",
)
else:
self.log("SUCCESS", "[CSP] CSP reporting endpoint configured")
for cdn in CDNS_ALLOWLISTED_BUT_RISKY:
if cdn in raw_csp:
self.add_vuln(
title=f"CSP Allowlists Risky CDN: {cdn}",
severity="Low",
category="Content Security Policy",
cvss_score=3.5,
description=f"The CSP allowlists `{cdn}`. Public CDNs host thousands "
"of packages; if any contain malicious code or are compromised, "
"your CSP provides no protection.",
remediation="Pin specific script hashes instead of trusting entire CDN origins. "
"Use Subresource Integrity (SRI) for all external scripts.",
evidence=f"CDN {cdn} found in CSP allowlist",
payload=cdn,
request_details=f"GET {self.target}",
response_details=f"CSP allowlists {cdn}",
confidence="Medium",
)
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