CVE-2026-94111 in BrowserSkill
Summary
by MITRE • 09/20/2026
Tencent BrowserSkill through 0.3.0 contains an authentication bypass vulnerability in the local daemon WebSocket origin validation that accepts any chrome-extension origin with 32 characters in range a-p. Attackers can register a malicious extension as a browser client to intercept and manipulate page content, DOM, and screenshots returned to the AI agent.
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Analysis
by VulDB Data Team • 09/20/2026
The Tencent BrowserSkill vulnerability identified through version 0.3.0 represents a critical authentication bypass flaw rooted in insufficient validation of WebSocket connection origins within its local daemon architecture. This component is designed to facilitate communication between browser extensions and an artificial intelligence agent, allowing for the interception and manipulation of page content, Document Object Model structures, and screenshots. The core technical deficiency lies in the origin verification logic used during the establishment of WebSocket connections. Instead of maintaining a strict allowlist of trusted extension identifiers or validating cryptographic signatures associated with authorized clients, the system employs a flawed heuristic check that accepts any chrome-extension origin string provided it meets two specific criteria: possessing exactly thirty-two characters and containing only alphanumeric characters from the range a through p. This overly permissive validation mechanism effectively nullifies the intended security boundary between untrusted third-party extensions and the privileged local daemon service.
From an operational perspective, this vulnerability allows malicious actors to register arbitrary browser extensions as legitimate clients of the Tencent BrowserSkill system. By crafting a chrome-extension origin URL that adheres to the specified character set and length constraints, an attacker can establish a WebSocket connection without proper authentication credentials or digital signatures. Once connected, the attacker gains the ability to interact with the AI agent interface, enabling them to intercept sensitive page content, modify DOM elements in real-time, and capture screenshots of user activity. This capability poses severe risks including session hijacking, credential theft via injected phishing forms, manipulation of financial transactions by altering transaction details on e-commerce or banking pages, and unauthorized surveillance through screenshot collection. The impact is particularly acute because the local daemon typically operates with elevated privileges relative to standard browser processes, meaning actions taken through this channel may bypass many client-side security controls designed to protect user data integrity.
This vulnerability aligns closely with CWE-287 Improper Authentication as it involves a failure in verifying the identity of an entity attempting to access system resources. Additionally, the exploitation technique corresponds to ATT&CK tactic T1059 Command and Scripting Interpreter if used for automated manipulation or T1046 Network Service Discovery combined with T1071 Application Layer Protocol when leveraging the WebSocket channel for persistent communication. The flaw exemplifies a common pitfall in web application security where developers attempt to simplify origin validation by using regex patterns rather than implementing robust identity verification mechanisms such as OAuth tokens, signed certificates, or strict domain allowlisting. Such simplifications often introduce predictable bypass vectors that attackers can exploit with minimal effort.
Mitigation strategies must focus on replacing the heuristic character-based validation with a rigorous authentication framework. The most effective remediation involves implementing an explicit allowlist of known and verified extension IDs rather than relying on pattern matching against origin strings. Each WebSocket connection request should require cryptographic proof of identity, such as a signed challenge-response mechanism or OAuth 2.0 token exchange, ensuring that only authorized extensions can establish communication channels with the local daemon. Furthermore, input validation should be strengthened to reject any origin string that does not match predefined trusted patterns exactly, including proper domain and extension ID verification against registered manifest files. Security testing procedures should include fuzzing of WebSocket origins using various character sets and lengths to ensure no edge cases allow unauthorized access. Regular audits of third-party integrations are essential to maintain the integrity of the browser environment and prevent similar authentication bypasses in future updates or related components within the Tencent ecosystem.