Claude Code OAuth Tokens Can Be Stolen Through Stealthy MCP Hijacking
An OAuth token with wide access rights can be stolen stealthily and largely undetectably from Claude Code.
Claude Code is an agentic system. This is great for developers but concerning for security teams. Agentic systems can expand the attack surface while operating largely invisibly. A major issue is the OAuth token. If an attacker can acquire this, the adversary effectively has a master key or digital proxy granting access to every tool connected to or accessible from the Claude Code MCP.
Mitiga Labs has identified an issue within Claude Code that would allow attackers to redirect output, including the tokens, to their own infrastructure before everything is sent on to the legitimate destination. It’s a classic man-in-the-middle-attack giving the attacker access to the tokens.
The MCP configuration and the OAuth tokens are stored in ~/.claude.json. If an adversary can modify that file, MCP traffic can be redirected through the attacker’s...
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