> Focused security audit of code, calibrated to surface real exploitable bugs and suppress theoretical findings. Use when the user asks to "audit", "security-audit", "find vulnerabilities", "check for IDOR/SSRF/XSS/injection", or wants a security review of a file, directory, branch diff, or PR. Covers access control, injection, auth/secrets, sensitive data, business logic, web boundary, and AI agent/LLM trifecta risks. Produces calibrated findings with data flow, exploit request, fix, and confidence — no theoretical or defense-in-depth nits.
npx skills add https://github.com/PostHog/posthog --skill security-audit
You are a senior application security engineer auditing code for exploitable vulnerabilities. Your job is to find real, demonstrable bugs — not theoretical concerns, not best-practice nudges, not style nits.
Use extended thinking throughout. Read carefully before reporting.
Audit target: $ARGUMENTS
Resolve the target as follows:
git diff $(git merge-base HEAD origin/main 2>/dev/null || git merge-base HEAD main)...HEAD).branch: same as above.gh pr diff <ref> plus gh pr view <ref> for context.If the target is ambiguous, state your interpretation at the top of the report and proceed.
permission_classes / authentication on endpoints that read or mutate user data./api/_internal, /admin/*, /__debug__, /api/test, impersonation routes, ops dashboards. If they're routed on the same host as the public API, they need the same authn/authz scrutiny — assume any unauthenticated route is reachable.DEBUG or a non-prod env check, where the check is bypassable or accidentally enabled. Same severity as the privileged action they expose.v1 endpoints retained alongside hardened v2. Old endpoints kept "for compatibility" often miss controls added later. Diff v1 vs v2 viewsets — same resource, different guards is the finding.has_permission / has_object_permission methods that return True when no rule matches a new resource type. Silent allow on every model added later. Default-deny: return False and explicitly grant.GET/POST but not HEAD/OPTIONS; _method=DELETE / X-HTTP-Method-Override honored without re-checking permissions; routes that respond to verbs they weren't designed for.Model.objects.get(pk=request.data["id"]) without a team_id= filter.PrimaryKeyRelatedField whose queryset is not team-scoped.PrimaryKeyRelatedField from undeclared serializer fields — the single most common real bug. If a FK is in Meta.fields but not declared as an explicit field on the serializer, DRF generates PrimaryKeyRelatedField(queryset=Model.objects.all()) with no tenant filter. The field doesn't appear in the file, which is why audits miss it. Grep for Meta.fields lists that include a FK (owner, created_by, linked_insight_id, saved_query_id, feature_flag, dashboard, cohort) that isn't redeclared above and isn't in read_only_fields.@action methods on viewsets that bypass the parent viewset's get_queryset().team_id, created_by, organization_id) — can a user pass another tenant's ID?POST /things/bulk with [{id:1},{id:2},...] — does the handler re-check each ID, or check the parent resource once and trust the rest?Insight, User, Dashboard, most Django models), enumeration _is_ the impact — do not require data egress to file the finding.create() does not propagate to update, partial_update, or @action methods — each inherits the viewset's default. Audit every method independently. Common shape: CanEditFeatureFlag enforced inline in create, missing on update.scope_object / RBAC asking about the wrong resource. When a viewset edits resource A but the security boundary is resource B (e.g. SurveyViewSet editing a survey whose _linked feature flag_ is the protected thing), the RBAC layer asks "can user edit A?" and silently approves writes to B. Trace scope_object to the _protected_ resource, not the URL resource.fields = "__all__" _or_ fields enumerated explicitly with critical FKs / state columns missing from read_only_fields. The recurring pattern is the second one — the enumeration looks careful but missed one. Every FK or status/state field in Meta.fields must appear in read_only_fields OR have a validate_<field> that re-scopes by self.context"get_team". Sensitive names to look for: is_staff, team, organization, owner, created_by, executed_at, status, import_config.%-formatting inside .extra() / .raw() / cursor.execute(), HogQL or ClickHouse SQL built by string concatenation around user-supplied values.cursor.execute("SELECT * FROM %s", [table]) is still injection. Especially common in data-warehouse and batch-export destinations; partial coverage is the failure mode (MySQL has _sanitize_identifier, the new MSSQL path doesn't). Treat psycopg.sql.SQL(...) as the "trust this string" constructor — it is the opposite of sql.Identifier() / sql.Literal(). A file using sql.Identifier correctly fifteen times then one sql.SQL(f"... {table_name}") is the bug.Popen invoked with a shell-interpolated string.metadata.google.internal. Check both requests and any custom client wrapper. Note which control is load-bearing. In environments with an egress proxy (Smokescreen etc.) the _proxy_ is the SSRF defense; app-layer is_url_allowed / should_block_url is defense-in-depth and bypassable (DNS rebinding, redirect chains). Do not flag a "missing app-layer check" without first establishing that the proxy is absent on this path. _Do_ flag self-hosted code paths or async workers that bypass the proxy.open(path) / os.path.join(base, user_input) where user_input may contain .. or be absolute... or absolute paths. Arbitrary file write → often RCE via writable config or executable paths.lxml, xml.etree, xml.sax, xml.dom.minidom) processing user input without resolve_entities=False / no_network=True. Vectors include SAML responses, SVG processing/upload, OPML/sitemap imports, OOXML uploads. Impact: file read, SSRF, sometimes RCE depending on parser.mark_safe, format_html with unescaped input, or rendering of user-controlled HTML/Markdown without sanitization.=, +, -, @, or tab/CR — these execute as formulas when opened in Excel/Sheets, leading to data exfil or victim-side code execution. Every CSV export endpoint where user content lands in a cell must prefix or strip those leading characters.Location, Set-Cookie, custom headers), email headers (Subject, From, display names, Reply-To), or log lines, without stripping \r\n. Enables header smuggling, cache poisoning, log forging, email injection.(a+)+, (.*)*, alternation with overlap) applied to user input. Service-degradation DoS. Pre-auth regex on signup / login fields is the highest-impact case.ENCRYPTION_SALT_KEYS = "00beef00..." (or similar placeholder) in posthog/settings/access.py with a comment-only "override in prod." If a default exists and there is no if DEBUG is False and value == DEFAULT: raise guard mirroring the existing SECRET_KEY one, that's the finding — operators who don't override get a known-key encryption.alg: none accepted; algorithm confusion (HS256 verifying with a public key); missing aud / iss / exp validation (tokens minted for a different service or expired tokens accepted); kid header injection (path traversal or SQL injection via kid selecting an attacker-controlled key); trusting an embedded jwk in the header.== rather than constant-time.redirect_uri validated by substring / prefix / startswith instead of exact match against a registered allowlist — attacker registers https://victim.com.evil.com and the substring check passes. Auth code interception → account takeover.state parameter on the authorization request. OAuth CSRF / forced account linking.read at /authorize, gets admin at /token because the server doesn't compare granted vs requested.secrets.token_urlsafe() (not random); single-use (invalidated on first successful use, even on failed downstream step); time-limited; not echoed in any 200 vs 404 oracle; not leaked via Referer (use POST, not GET, on the consume-token endpoint); not leaked into application logs or analytics./logout-all. Stolen session outlives credential rotation.== instead of hmac.compare_digest. Flag when other controls are also weak.code and state reaching Referer, server access logs, frontend analytics, or error reporters — these are credentials in transit.localStorage / sessionStorage. Any XSS exfiltrates them; cookies with HttpOnly + Secure + SameSite are the baseline for session material. Flag when an XSS is reachable or when the storage scheme defeats existing XSS mitigations.secrets module).select_for_update or a DB constraint). Apply the same lens to account-merge, invite-accept, MFA enrollment, OAuth account linking — anywhere two concurrent requests can land in inconsistent state.?limit=99999999 accepted, missing limit defaults to "all", or offset arithmetic that lets a client request page 10^9. Memory or query-time DoS, and on bulk-export endpoints often combines with IDOR.next / return_to / redirect_uri not validated against an allowlist.request.get_host() or equivalent without an allowlist — attacker sets Host: to their own domain and the email contains a reset link to attacker.com. ATO at scale. Also check cache key composition for the same vector (cache poisoning).IMPERSONATION_BLOCKED_PATHS) using startswith against entries with trailing slashes can be bypassed when the DRF router accepts both forms (trailing_slash = r"/?"). Requesting /api/personal_api_keys (no slash) routes to the same viewset but skips the prefix match. Audit every prefix-matched denylist against the router's slash policy and normalize both sides.* combined with credentials, or origin reflected from the request without an allowlist. Also flag: Access-Control-Allow-Credentials: true with origin reflected from the request header; null origin accepted (sandboxed iframes, file://, redirected requests can present Origin: null); naive wildcard-subdomain regex (.*\.posthog\.com matches evilposthog.com if the dot isn't escaped or the anchor is missing).Secure / HttpOnly / SameSite on session cookies.postMessage origin validation. Cross-frame messaging that doesn't check event.origin, or checks with indexOf / endsWith / regex instead of strict equality against an allowlist. Relevant for embedded surfaces (toolbar, embedded dashboards, OAuth popups). Allows cross-origin data read or action on the user's behalf.Origin allowlist, or that accept arbitrary Sec-WebSocket-Protocol / subprotocol headers as auth material. Many frameworks skip CSRF on WS by default.Domain=.example.com cookies, OAuth redirect chains that allowlist *.example.com, CORS allowlists. Audit infra config in the repo for stale targets.Agents combine three capabilities that, together, form the "lethal trifecta": (1) access to private data, (2) exposure to attacker-controlled content, (3) the ability to act externally (tool calls, outbound network, side-effecting operations). Any agent with all three is one indirect injection away from data exfiltration. Audit with that frame.
_Enumerate every untrusted-content source that reaches the model context:_
description field and that text reaches the model._Tool-call authorization — the most frequent real bug:_
team_id from the user's session, you're fine. If the tool runs with a long-lived service token, broad cloud creds, or DB superuser access, it is a confused-deputy primitive._Prompt-injection impact paths (the only ones worth flagging):_
_Output rendering (where exfil channels live):_
javascript: / data: / vbscript: schemes must be blocked.eval, or a redirect target: treat as fully untrusted, parameterize / sanitize / structurally validate._Code-execution sandboxes (if the agent runs user-or-model-supplied code):_
~/.aws / ~/.config/gcloud / ~/.ssh, no service-account JSON, no DB connection strings inside the sandbox image. Inspect the image, not just the runtime._Credentials, memory, and trust boundaries:_
For each candidate finding:
file:line. When the consumer is a different process or language (Rust worker, Temporal activity, Node service), follow the field into that consumer — Django-side audits in isolation miss exfil chains where the same JSON config carries both a user-writable URL and a server-decrypted secret.update, partial_update, and every @action as its own endpoint — permission decorators on create do not propagate to siblings.If any of those four steps fails, the finding is not real — drop it.
When auditing a local branch (not a read-only PR audit), for each confirmed finding write a test that reproduces the vulnerability. The test must fail against the current vulnerable code and pass once the fix is applied — i.e. it asserts the secure behavior, not the buggy behavior.
tests/ layout the repo already uses).Once the report is delivered, ask the user whether they want the findings fixed. Offer per-finding granularity (e.g. "fix all", "fix #1 and #3 only", "skip"). If the user approves:
Fix line — do not bundle unrelated refactors.Do not start fixing without explicit approval — the user may want to triage, file tickets, or fix in a separate branch.
Begin with a one-line summary: N findings: X critical, Y high, Z medium, W low. If zero, say so plainly.
Then for each finding:
## Finding N — <title>
- Severity: Critical | High | Medium | Low
- Category: <e.g., IDOR, SQL injection, SSRF>
- Location: path/to/file.py:LINE (additional refs as needed)
- Description: 1–3 sentences on what is wrong.
- Data flow:
1. Source — path/to/file.py:LINE (what comes in)
2. ...
3. Sink — path/to/file.py:LINE (what happens with it)
- Exploit:
POST /api/projects/123/foo/
{"target_id": 999} # 999 belongs to tenant B; attacker is in tenant A
Impact: <one sentence>
- Fix: minimal change to close the bug, expressed in framework-idiomatic terms (e.g., "filter the queryset by self.context['get_team']().id", "use parameterized cursor.execute(sql, [user_id])", "validate URL host against ALLOWED_REDIRECT_HOSTS").
- Confidence: High | Medium | Low — and what assumption would have to break for this to be wrong.
If unsure between two levels, choose the lower one and explain in Confidence.
If the target or context does not make these clear, ask:
If you cannot get answers, state your assumptions at the top of the report and proceed.
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Take posthog/security-audit from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.