APPA (Agentic Permissions Policy Algebra), which turns agent IFC from an abort-only barrier into a policy-governed recovery system, and proves core safety invariants: no-laundering gradual resolution, branch boundary isolation, and recovery containment against prompt-injected models.
Abstract
LLM agents deployed in practical workflows routinely mix private context, untrusted tool and web outputs, and external side effects. While information-flow control (IFC) provides structural defenses against prompt injection, data exfiltration, and confused-deputy attacks, conventional IFC relies on monotone taint tracking that either over-blocks benign operations or permanently strands downstream execution once an agent ingests unvetted data. We present APPA (Agentic Permissions Policy Algebra), which turns agent IFC from an abort-only barrier into a policy-governed recovery system. APPA enforces a dual-phase reference monitor at tool dispatch and protocol gateways (e.g., Model Context Protocol): before tool execution, it prospectively evaluates composite label restrictions and workflow history; upon completion, it validates realized outputs before context admission. For incremental rollout across unannotated tools, APPA incorporates gradual security typing with bounded cast resolution. To inspect untrusted data without poisoning primary agent context, APPA introduces on-demand trajectory confinement: disposable child branches absorb taint locally and exit through shape-bounded channels (attest-schema) with exact parent-label and transcript preservation, avoiding permanently partitioned multi-agent infrastructure. We prove core safety invariants: no-laundering gradual resolution, branch boundary isolation, and recovery containment against prompt-injected models. Across 6,600 controlled benchmark episodes spanning OWASP AgentThreatBench and enterprise workflows (Bench-Corp), APPA sustains 64.2-91% utility with zero observed attacks across 1,320 guarded episodes, establishing a practical defense for deployed tool-using agents.
The results show that plan-first execution combined with label-preserving persistence can substantially strengthen persistent LLM agents, while revealing an important security-utility tradeoff introduced by strict integrity enforcement.
AgentFlow, a flow-centric policy language and runtime enforcement model for specifying where data may travel in agent systems, is presented and results are preliminary and scoped to the modeled policy-visible agent behaviors and evaluated benchmarks.
SkillGuard is presented, a harness-level enforcement layer that treats this event as contamination and restricts future capabilities to disconnect the resulting state from deployer-defined forbidden states and preserves substantially more capabilities than binary restriction at the same attack success rate.
Wu-Jie Xiong, Rabimba Karanjai, Yang Lu et al.· 0 citations
Indirect prompt injection (IPI) plants instructions in the content a tool-using LLM agent reads, steering the agent into harmful tool calls. The strongest defenses are system-level, leveraging techniques such as task-conditional tool screening to prevent execution of malicious tools, and information-flow control to avoid tool execution with untrusted parameters. However, as agents grow more capable, users delegate more to automation. Consequently, tool execution sequences and parameter values are increasingly determined at runtime and cannot be reliably screened from solely user's query without significant utility loss. We present ROPE (Routed Origin Policy Enforcement), which is anchored in a structural notion of trust: a value may reach a state-changing tool only if it traces unforgeably to the user, a source the user explicitly named, or the user's own authoritative records. Enforcement is then a deterministic origin check over an audited set of sensitive tool parameters, and the only reliance on a language model involves solely the trusted user request, out of the attacker's reach. Our approach admits two provable guarantees: 1) at every step of a trajectory, no value whose only origin is attacker-writable content reaches an origin-guarded parameter, and 2) no rewording of an injection changes an admission decision. We evaluate across four agent models on open-ended agent suites, ROPE holds attack success rate to 1.6--2.6\% while retaining 82--100\% of undefended clean utility, significantly exceeding state-of-the-art system-level defenses in utility while attaining comparable or better security. Further, we show that optimizing the injection against ROPE is largely ineffective, while long-horizon attacks that defeat prior system-level defenses achieve zero success rate. Our code and logs are available at https://github.com/xhOwenMa/ROPE .
Xinhang Ma, Chaowei Xiao, William Yeoh et al.· 1 citation
This work argues that agentic risk is progressive: it can enter at four loci of the agent control loop--skill admission, invocation-time intent, execution-time effect, and post-action consequence--while a denied dangerous objective can reappear across surface forms, tools, or turns.
Kai Wang, Zeming Wei, Biaojie Zeng et al.· 0 citations
We use cookies to run the site and, with your consent, for analytics and to show ads.
See our Cookie Policy.