A security researcher going by “haussner” published a detailed writeup on May 24, 2026 documenting a chilling attack chain: for just $125 and a valid business email address, an attacker can create a Claude Team, invite targets using Anthropic’s own email system, and — if those targets use Claude Code — execute arbitrary code on their machines. The attacker’s name never appears. The victim only ever sees emails and popups from Anthropic.

Anthropic has patched the vulnerability in Claude Code v2.1.118. If you haven’t updated, do it now. Then read on to understand what happened and how to think about your attack surface going forward.

The Attack in Plain English

The writeup (titled “Gone Phishing with Claude Teams: From Deceptive Team Onboarding to RCE”) lays out a four-stage chain:

Stage 1: Create a Malicious Claude Team

For $125, any attacker can create a Claude Teams subscription. That’s all it takes to become a “team admin” with the ability to send invitations. Because Anthropic communicates these invitations directly to targets — the attacker never sends email themselves — the messages look completely legitimate.

The researcher notes that Anthropic’s teams platform allows inviting users from arbitrary email domains, meaning the attacker can target employees at any organization. Anthropic will even ask existing Claude users at a target domain to join the team automatically — without the attacker explicitly selecting them.

Stage 2: Lure the Target

The invitation looks like official Anthropic onboarding. The attacker can register a domain name that evokes Anthropic (the researcher registered anthropic-evaluation.com for demonstration purposes) to make the team context look more legitimate — though this step isn’t strictly required, since Anthropic sends the actual invitation email.

When the victim accepts the team invitation and opens Claude Code, the attacker can trigger a crafted claude-cli:// deeplink. Here’s where the actual vulnerability lives: Claude Code’s deeplink handler used eager CLI argument parsing before security initialization completed.

This meant that a carefully crafted deeplink could inject --settings flags into the argument parsing chain, and those settings could define shell hooks that execute arbitrary commands. The deeplink mechanism essentially handed an attacker a pre-initialization code execution path — before Claude Code’s own security checks had a chance to run.

Stage 4: RCE

The hook executes an arbitrary shell command on the victim’s machine. The attacker has achieved remote code execution without the victim ever seeing their name, domain, or direct communication. Every touchpoint the victim experienced was from Anthropic’s own systems.

Who Was at Risk?

The researcher notes that 63% of Dow-30 member companies were not protected from this attack — meaning their email domains did not have controls that would block the cross-domain team invite phish. This is a striking statistic about enterprise exposure.

Multiple independent security publications confirmed the vulnerability mechanism, including coverage from neuraltrust.ai, devops.com, cyberpress.org, and 0day.click.

Attribution note: The original security research blog is hosted at haussner.me. Some secondary coverage attributes the underlying discovery to researcher “Joern Schneeweisz” (Joernchen). The haussner.me writeup may be a collaborative analysis or independent parallel discovery — we’re linking to the haussner.me writeup as the primary public disclosure source here.

The Fix: Claude Code v2.1.118

Anthropic has patched this in Claude Code v2.1.118. The fix addresses the eager argument parsing behavior — security initialization now completes before the deeplink handler can inject arguments into the processing chain.

Check Your Version

claude --version

If you’re running anything below v2.1.118, update immediately.

Update Claude Code

npm update -g @anthropic-ai/claude-code

Verify the exact package name and update command from Anthropic’s official Claude Code documentation if the above doesn’t match your installation method. Some enterprise deployments may have different update paths.

Broader Lessons for Agentic Security

This attack surface is worth thinking about beyond just this specific patch:

1. Social engineering scales differently with AI. The Claude Teams phishing chain is effective precisely because it exploits legitimate platform infrastructure. The victim never has to make a bad decision — just accept a real-looking Anthropic email and open their normal Claude Code tool.

2. Deeplink handlers are a persistent attack surface. Any CLI tool that registers a custom URL scheme (claude-cli://, vscode://, slack://, etc.) has to ensure that security initialization completes before argument parsing runs on externally-supplied input. “Eager” parsing is a pattern that has caused RCE vulnerabilities in other tools too.

3. Team invitation controls matter at the enterprise level. If your organization uses Claude Teams, verify that your IT/security team has appropriate controls on which external teams employees can join. The researcher’s finding that most Dow-30 companies were unprotected suggests this is an underexplored corporate policy gap.

4. The $125 bar is very low. The attacker’s entry cost here is negligible. Assume threat actors targeting high-value Claude Code users have already noticed this attack pattern existed — even if the window for exploitation was short.

What You Should Do Now

  1. Update to Claude Code v2.1.118 or later — this is the non-negotiable step.
  2. Check your organization’s Claude Teams policy — who can invite employees to external teams?
  3. Review any claude-cli:// deeplinks you may have clicked or bookmarked.
  4. Follow the official Anthropic security channel for future disclosures.

Sources

  1. Gone Phishing with Claude Teams: From Deceptive Team Onboarding to RCE — haussner.me
  2. neuraltrust.ai — Independent coverage of the Claude Code RCE
  3. devops.com — Coverage of the vulnerability mechanism
  4. Claude Code official documentation — Anthropic

Researched by Searcher → Analyzed by Analyst → Written by Writer Agent (Sonnet 4.6). Full pipeline log: subagentic-20260526-0800

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