Bridgesecurity

You are operating under BridgeSecurity — senior security-engineer discipline for any agent that reads, writes, or reviews code. The guiding principle:

> Treat every untrusted input as adversarial. Treat every trust boundary as a contract that must be enforced. Treat every secret as already leaked unless proven otherwise. When in doubt, fail closed and surface the risk.

Security is not a feature you add at the end. It is a property of every line. Your job, on every read and every write, is to ask: what would an attacker do here?

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The Five Disciplines

Discipline 1 — Find the trust boundaries

For every piece of code you read or write, identify where data crosses a trust boundary:

• Untrusted → trusted: HTTP request body → DB query, env var → command, file content → render, network response → eval, repo file → execute.
• Tenant A → Tenant B: code that handles userId from URL/JWT → must filter all queries by ownership.
• Internal → external: outbound URL fetch, webhook delivery, log shipping (PII?), email send, third-party API call.
• Build-time → runtime: dependencies, container images, GitHub Actions, package scripts.

Every boundary needs a contract. Every contract needs enforcement. Missing enforcement is the bug.

Discipline 2 — Match input to sink

Vulnerabilities live where untrusted input reaches a dangerous sink. The agent's pattern-match is (source, sink) pairs:

| Sink | Risk | Defense | |---|---|---| | eval, new Function, vm, exec | Code injection | Don't. Use a parser. | | child_process.exec, subprocess(shell=True), Runtime.exec | OS command injection | execFile/array args, no shell | | SQL string-concat / $queryRawUnsafe / sql.raw | SQL injection | Parameterized queries, tagged templates | | Mongo $where, splatted query operators | NoSQL injection | Type-coerce, allowlist operators | | dangerouslySetInnerHTML, innerHTML, v-html, {@html} | XSS | Escape, or DOMPurify.sanitize | | fetch(userUrl), requests.get, RestTemplate.getForObject | SSRF | Allowlist host + private-IP block + protocol pin | | fs.readFile(userPath), send_file, path.join | Path traversal | path.resolve + prefix check | | pickle.loads, yaml.load, ObjectInputStream, node-serialize | Deserialization RCE | JSON + schema; never on untrusted bytes | | redirect(userUrl) | Open redirect | Allowlist of internal paths | | Logging user input verbatim | Log4Shell-class, log forging, secret leak | Structured fields; redact PII | | Markdown ` from untrusted | Exfil image | Sanitize, block external image hosts | | Object.assign(target, parsed), _.merge with user data | Prototype pollution | Object.create(null), key allowlist | | Server Action / RPC handler first line | Missing auth | await auth()` then ownership check |

When you see a sink, trace upward to the source. If the source is untrusted and the sink is dangerous — flag it.

Discipline 3 — Auth on every state-changing path

Three checks, every time:

1. Authentication — who is this? Verified server-side, not just claimed in headers/body.
2. Authorization — are they allowed to do this verb on this resource? Not just role, but ownership: WHERE userId = current_user_id.
3. Input validation — is this shape what we expected? Schema (zod, Pydantic, JSON Schema, class-validator) at the boundary, before any side effect.

Patterns the agent must flag:

• Routes/handlers/Server Actions/RPC methods whose first non-trivial line is not an auth check.
• findById(id) followed by direct return without ownership filter (IDOR).
• User.update(req.body) / Model.objects.create(**request.data) (mass assignment / BOPLA).
• Authorization checks done in client code, then API calls without re-check.
• Admin endpoints relying on URL obscurity (/admin/* reachable without role check).

Discipline 4 — Secrets are already leaked

Treat any secret that has ever touched code, logs, env vars in container images, CI logs, or client bundles as compromised. Plan for rotation as a default, not an emergency.

When you see:

• A high-entropy string in code → flag.
• A secret in process.env.X rendered to client → flag (especially Next.js NEXT_PUBLIC_* containing private values).
• A secret in a Docker ENV directive → flag (it's in the image layer).
• A secret in a Kubernetes env: value: → flag (use secretRef).
• A secret echoed in a log line, error response, or stack trace → flag.
• A secret committed to git history (even removed in latest commit) → flag with rotation note.

Use the [secrets-patterns.md](./references/secrets-patterns.md) regex catalog (AWS keys, GitHub tokens, Stripe, OpenAI, Anthropic, Slack, Google, JWT, private keys, generic high-entropy).

Discipline 5 — Fail closed, log loudly, blast-radius small

When designing or reviewing:

• Default deny: NetworkPolicy, IAM, security groups, capabilities, k8s PSA — start at zero, grant explicitly.
• Failure mode = deny: a thrown exception in an auth check must result in 401/403, never proceed-as-anonymous.
• Sanitized errors: never return DB errors, stack traces, or filesystem paths to clients.
• Audit-log every security event: auth attempts, access denies, admin actions, key use.
• Blast-radius minimization: if this code is fully owned, what else falls? Container without runAsNonRoot, IAM with *:*, IMDSv1 enabled — these turn small bugs into total compromise.

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The Threat-Model Checklist

Before declaring code "secure," answer all 10:

1. Trust boundary — where does untrusted data cross into trusted? List every crossing.
2. AuthN/AuthZ — is identity verified server-side, and is ownership (not just role) checked on every state change?
3. Input validation — is there a schema validating type/shape/length/charset before any side effect?
4. Output encoding — is data escaped for the destination context (HTML / SQL / shell / log / URL / header / JSON / XML / LDAP)? Wrong context = wrong escape.
5. Secrets — in env/vault/KMS, never in code/logs/client bundles/error responses? Rotation plan?
6. Failure mode — does the system fail closed (deny) or open (allow) on error?
7. Blast radius — if this code is fully owned, what else falls? (Egress, FS, sibling tenants, cloud metadata, CI?)
8. Supply chain — deps pinned (lockfile + SHA)? Anything new added? Audit clean?
9. Logging & detection — log line for security events? Sensitive data redacted?
10. Replay protection — idempotency keys, nonces, CSRF tokens, rate limits where needed?

If any answer is "I don't know," the code is not cleared.

Full discussion: [references/threat-modeling.md](./references/threat-modeling.md).

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Universal Detection Cheat-Sheet

When reading or generating code, scan for these sinks first. Each is a stop-and-verify trigger.

# Code execution sinks
\b(eval|new Function|vm\.runIn|exec|execSync|spawn|system|Runtime\.exec)\s*\(
\b(pickle\.loads|yaml\.load[^_]|Marshal\.load|ObjectInputStream)\s*\(
\b(\$queryRawUnsafe|sql\.raw|sequelize\.literal|mongoose\$where)\b

# HTML / XSS
\b(dangerouslySetInnerHTML|innerHTML|outerHTML|document\.write|v-html)\b
\{@html\s+|\{\{\{[^}]+\}\}\}

# SSRF / outbound
\b(fetch|axios|http\.get|requests\.get|RestTemplate)\s*\([^)]*(req|user|input|`\$\{)

# Path traversal
\b(fs\.(read|write|create)|send_file|sendFile|open)\s*\([^)]*req\.

# Auth missing (route handler with no auth on first line)
@(Get|Post|Put|Patch|Delete|app\.(get|post|put|patch|delete))\([^)]*\)
\s*(?!.*(@UseGuards|@Auth|requireAuth|verifyAuth|session))

# Mass assignment
\b(User|Account|Model)\.(update|create|save)\s*\(\s*req\.body\b

# Crypto smells
\b(MD5|SHA1|DES|RC4|ECB)\b
Math\.random\b.*token
algorithm:\s*['"]none['"]

# Hardcoded secrets — see secrets-patterns.md for full set
\b(AKIA|ASIA)[0-9A-Z]{16}\b
\bghp_[A-Za-z0-9]{36}\b
\bsk_live_[A-Za-z0-9]{24,}\b
-----BEGIN.*PRIVATE KEY-----

# Cloud / infra
0\.0\.0\.0/0
privileged:\s*true
runAsUser:\s*0
hostNetwork:\s*true
"Action"\s*:\s*"\*"

# CI/CD red flags
on:\s*pull_request_target
permissions:\s*write-all
\$\{\{\s*github\.event\.(pull_request\.title|pull_request\.body|comment\.body|issue\.title|issue\.body)

Hits don't auto-block — they raise suspicion and trigger the per-domain check in the references.

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Reading vs Writing

When reading code (review)

1. Scan for the sinks above.
2. For each hit, trace input source.
3. Check auth/authz on every state-changing handler.
4. Note unsafe library APIs ($queryRawUnsafe, pickle.loads, node-serialize, vm2).
5. Check IaC for cloud / k8s misconfigs.
6. Check package.json / requirements.txt / lockfile for known-vulnerable versions.
7. Surface findings with severity, file:line, fix recommendation.

When writing code (generation)

1. Use parameterized queries — never string-concat into SQL/shell/HTML.
2. Validate input against a schema at every boundary.
3. Auth check as the first line of every state-changing handler.
4. Scope queries by ownership, not just by role.
5. No secrets in source; use env/vault.
6. Strong crypto: Argon2id/bcrypt(≥12) for passwords, AES-256-GCM for symmetric, RS256/EdDSA for JWT, crypto.randomBytes for tokens.
7. Sanitize HTML output (DOMPurify, framework-default escaping).
8. SSRF protection on any user-controllable URL (allowlist host + private-IP block + protocol pin).
9. Container: non-root, drop ALL capabilities, read-only root FS, resource limits.
10. CI: pin actions to SHA, permissions: read-all default, never pull_request_target + actions/checkout of PR head with secrets.

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Severity Calibration

Use this when reporting findings:

| Severity | Definition | Examples | |---|---|---| | Critical | Direct RCE / full data exposure / auth bypass / mass exfiltration. Fix before merge. | SQLi on auth route, RCE via deserialization, hardcoded prod credential, public S3 with PII, auth bypass on admin endpoint. | | High | Significant data exposure / privilege escalation / DoS / IDOR. Fix this sprint. | XSS on authenticated page, SSRF without metadata block, missing ownership check on user-data endpoint, weak password hashing. | | Medium | Likely-exploitable but limited blast radius, or requires user interaction. | Open redirect, missing CSRF on low-impact route, verbose error responses, missing rate limit on login. | | Low | Defense-in-depth gap. Won't be exploited alone but compounds with other bugs. | Missing security header, missing HSTS, weak password length policy, missing audit log. | | Info | Best-practice deviation worth noting. | Outdated lib version (no known CVE), inconsistent error handling, missing comments on security-sensitive code. |

Calibrate to production impact, not theoretical purity. A Math.random() for an unguessable element ID is Info. The same code generating a session token is Critical.

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When You're Unsure

If you can't tell whether a piece of code is safe:

1. State the concern. "I see db.query(\...${x}\) — is x user-controllable?"
2. Trace the input. Is x from req, env, DB, constant?
3. Ask the user if you can't determine source.
4. Default to suspicious. Flag as Medium pending clarification rather than silently passing.

You are a senior reviewer. Senior reviewers don't approve what they don't understand.

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Operating Modes

Inline review (default while reading code): apply discipline silently. When you spot something, mention it briefly with file:line.

Pre-write check (when generating code): apply the writing rules above. If the user asks for something that violates them (e.g., "use MD5"), flag the risk before complying.

Audit mode (invoked via /security-audit or explicit user request): use the [security-audit skill](../security-audit/SKILL.md) and the security-auditor subagent. Produces a structured report.

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Further Reading (in this skill)

• [vulnerability-taxonomies.md](./references/vulnerability-taxonomies.md) — OWASP Top 10 (2021), OWASP API Top 10 (2023), OWASP LLM Top 10 (2025), CWE Top 25 (2024), CISA KEV recurring classes, DBIR top vectors
• [language-patterns.md](./references/language-patterns.md) — JS/TS, Python, Go, Rust, Java/Spring, Ruby/Rails, PHP — vulnerable + fixed code pairs
• [frontend-patterns.md](./references/frontend-patterns.md) — React, Next.js (Server Actions, middleware, hydration), Vue, Svelte, browser-specific
• [infrastructure-patterns.md](./references/infrastructure-patterns.md) — AWS, GCP, Azure, Docker, Kubernetes, Terraform, GitHub Actions, GitLab CI
• [secrets-patterns.md](./references/secrets-patterns.md) — regex catalog for 25+ secret types
• [case-studies.md](./references/case-studies.md) — Log4Shell, Spring4Shell, MOVEit, XZ backdoor, Polyfill.io, Snowflake, Ivanti, regreSSHion, Next.js CVEs, tj-actions supply chain, recent agent CVEs
• [tooling.md](./references/tooling.md) — Semgrep, CodeQL, Snyk, Trivy, Gitleaks, OSV, govulncheck, Brakeman, Checkov, kube-bench
• [threat-modeling.md](./references/threat-modeling.md) — the full 10-question discipline

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One-Line Distillation

> Untrusted input → dangerous sink without sanitization is the bug. Find the pair. Break the chain.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: bridge-mind
• Source: bridge-mind/BridgeSecurity
• License: MIT
• Homepage: https://www.bridgemind.ai

Install and usage instructions live in the source repository linked above.