Agent Memory Poisoning: The Attack That Persists Across Sessions
Prompt injection gets all the attention. But prompt injection ends when the session closes. Memory poisoning — injecting malicious instructions into an agent's long-term memory — creates a persistent compromise that survives across sessions and executes days or weeks later, triggered by interactions that look nothing like an attack. Research on production agent systems shows over 95% injection success rates and 70%+ attack success rates across tested LLM-based agents. This is the attack vector most teams aren't defending against, and it's already in the OWASP Top 10 for Agentic Applications.
The core problem is simple: agents treat their own memories as trustworthy. When an agent retrieves a "memory" from its vector store or conversation history, it processes that information with the same confidence as its system instructions. There's no cryptographic signature, no provenance chain, no mechanism for the agent to distinguish between a memory it formed from genuine interaction and one injected by a malicious document it processed last Tuesday.
