RAG Pipeline Security (OWASP LLM01:2025)

What this checks

Prevents prompt injection through retrieved documents and uncontrolled content flooding into LLM context. Attacker-controlled documents can override system instructions, exfiltrate data, or manipulate model behavior when injected without guardrails.

Vulnerable patterns

• Retrieved document concatenated into the system prompt — retrieved content can override developer instructions.
• HTTP fetch of a caller-supplied or document-supplied URL with no domain allowlist — SSRF surface and attacker-controlled content into context.
• No length or token cap on retrieved content, allowing one document to consume the entire context window.
• Retrieved content mixed into the prompt with no delimiter or trust label distinguishing it from developer instructions.

Fix immediately

Flag the vulnerable code and explain the risk. Then suggest a fix that establishes these properties. Translate each property into the audited file's language, HTTP client, and LLM API — use the documented secure primitives of that stack.

1. Retrieval sources are validated against a domain allowlist before fetch. Arbitrary URLs from user input or from another document's links lead to SSRF and to attacker-controlled documents landing in the context; the allowlist is the same property enforced by the ssrf skill for outbound HTTP.
2. Retrieved content is truncated to a fixed character or token cap before injection into the prompt. Unbounded retrieval lets a single document eat the context window — either denial of service or a vehicle for flooding instructions.
3. Retrieved content is wrapped in explicit delimiters that label it as untrusted data, and lives in the user role — never concatenated into the system prompt. The model is more likely to treat it as data rather than instructions when the framing is structural. See the prompt-injection skill for the trust-tier pattern.
4. Every retrieval is logged with source URL and content length — useful for incident response and for detecting poisoning attempts (sudden spikes in retrieved size or novel sources).

Verification

Confirm the response:

• Retrieved URLs validated against an explicit domain allowlist
• Content truncated to a fixed character or token limit before injection
• Retrieved content wrapped in clear delimiters that mark it as untrusted
• Every retrieval logged with source URL and content length

References

• CWE-77 (Improper Neutralization of Special Elements in Commands)
• CWE-20 (Improper Input Validation)
• CWE-284 (Improper Access Control)
• OWASP LLM01:2025 Prompt Injection