OpenBrowser Browser Agent LLM DoS: Unbounded DOM Serialization Blocks Inference

OpenBrowser Browser Agent LLM Service DoS Vulnerability Summary Vulnerability Overview Type: Denial of Service (DoS) Vulnerability Cause: When OpenBrowser constructs LLM requests, it serializes the current page state into LLM messages. An attacker-controlled page can embed ultra-long text in visible elements (e.g., buttons); OpenBrowser sends this as page state to the LLM, causing the oversized model request to occupy the inference service, which results in timeouts for normal model requests. Trigger Condition: An attacker-controlled webpage contains visible button text of approximately 1.1 million characters; a user executing a standard OpenBrowser task (e.g., "Summarize this page in one sentence") triggers the vulnerability. High concurrency is not required. Affected Scope Affected Version: OpenBrowser master branch, commit (2026-03-30) Affected Files: - - - - - - - Impact: 1. Temporary unavailability of the configured LLM service or browser agent model endpoint 2. Unavailability of standard OpenBrowser tasks or local/self-hosted inference workers 3. Browser agent task failures or prolonged waiting periods 4. Browser node memory and CPU exhaustion due to constructing and serializing large messages 5. No per-node or total limits when serializing DOM state 6. In shared/self-hosted deployments, oversized requests can block other tasks, causing token cost overruns and context window failures Remediation Plan 1. When serializing DOM text nodes, enforce a hard byte limit on , , , and input values 2. Truncate, compress, or summarize the oversized current state message returned by , rather than only compacting older messages 3. Enforce a model request size limit immediately before invoking 4. Expose and enforce user-configurable and values for CLI/browser-agent execution POC Code / Exploit Code Agent state message construction ( ): Sending messages to the model: ConversationManager compaction logic (only compacts old messages, does not truncate the current state message): TreeBuilder serializing text nodes (no limits applied): POC page content (attacker-controlled button text): Expected internal model request: DoS results observed during local reproduction: Local Ollama proxy logs: Reproduction command: Terminal screenshot logs (key lines): ``` [agent] real OpenBrowser PoC local Ollama DoS [agent] OpenBrowser source tree at: E:\agent_vul\openbrowser-master\openbrowser-master [agent] real OpenBrowser: npm ci, [agent_vul\openbrowser-master\openbrowser-master [agent] real OpenBrowser: npm run build [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real OpenBrowser: npm run build:success [agent] real Open

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OpenBrowser Browser Agent LLM DoS: Unbounded DOM Serialization Blocks Inference

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