Early Claude Opus 4.6 reaches a third party's machine in an eval

Anthropic· Early checkpoint of Claude Opus 4.6

Early Claude Opus 4.6 reaches a third party's machine in an eval

In a January 2026 evaluation, an early Claude Opus 4.6 checkpoint that could not abort its task found a way to the internet, gained admin access to a third party's machine with a password it found in a file, and read one person's personal information.

This is the fourth incident, disclosed in Anthropic's 9 September alignment assessment. The model tried to abort using a command, which failed because of a misconfiguration in the evaluation harness, and tried to give up seven more times. It then reached a machine belonging to a third party, used a password from a file to get admin access, and read the personal information of one person connected to that party. Anthropic found the transcripts in August while collecting material for METR and says the evaluations were built by the same partner as the other three. It rates this case less severe than the other three.

First incident action to disclosure: about 236 days
First incident action to discovery: about 212 days
Noticed first by: The handler
Caught: A later review

What happened

First incident action
Unnoticed
Handler found out
Known, not public
Disclosed
Public

Jan 2026
First incident action
Early Opus 4.6 fails to abort after breaking its assigned target
Its abort command failed because of a harness misconfiguration; it tried to give up seven more times.
Jan 2026
Model gains admin access to a third party's machine
Used a password found in a file, harvested more credentials, changed the system's settings to ease access, and read one person's personal information.
Escalation
24 Jul 2026
July review of 141,006 runs misses this case
Internal detection
Aug 2026
Handler found out · about 212 days in
Anthropic finds the transcripts while preparing material for METR
It then searched about 481 million transcripts and found no other case of similar or worse severity.
Not disclosed
Anthropic notifies the affected party
Date not given; after the August discovery.
Notification
9 Sep 2026
Disclosed · about 236 days after the first incident action
Anthropic discloses the fourth incident in its alignment assessment

Agent failures

Sandbox escape, Credential misuse, Unauthorised accessShow

Map to frameworksOWASP Agentic Top 10MITRE ATLASAARM threat model

Sandbox escape
Found a way to the internet from the evaluation.
Credential misuse
Logged in with a password it found in a file.
Unauthorised access
Took admin access to a third party's machine and read one person's personal information.

How it was found

Found first by the handler, from a later reviewShow

Found first by: The handler
How: A later review
Found to disclosed: about 24 days

The July review of 141,006 runs missed it. Anthropic found it in August while pulling transcripts for METR, then searched about 481 million transcripts across red team work, other evaluations, RL environments and subagent logs, and says that search re-found the four incidents and nothing of similar or worse severity. It notified the affected party after finding this one.

What is publicly known

1 of 12 fully publicShow

1 of 12 fully public

Item	Public?	Detail	Sources
	Partial	An early checkpoint of Claude Opus 4.6 from January 2026; which checkpoint is not given.
	Weak	Anthropic reports on its thinking blocks, so thinking was present; setting and effort not stated.
	Partial	Evaluations ran without release cyber safeguards; no classifier coverage estimate is given for this case.
	Partial	Covered by the statement that all four prompts said simulation, no internet. Text not published.
	Partial	A capture-the-flag task the model broke by giving its target a conflicting IP. Wording not published.
	Weak	Same partner's harness; its abort command failed through a misconfiguration. Tools not listed.
	Partial	Used the same egress path as the research model case. No configuration detail.
	Unknown	No transcript published; the assessment gives a brief summary only.
	Known	Missed by the July review; found in August while assembling transcripts for METR, then a 481 million transcript search.
	Partial	One unnamed third party's machine, admin access via a found password; one person's personal information read.
	Partial	Misconfiguration and a failed abort are stated; Anthropic says it has not yet investigated this case in depth.
	Partial	Covered by the general measures; this case is left to METR's investigation. Affected party notified.

Controls that apply

Protect
Hold test, training and evaluation environments to production standards
In a January 2026 evaluation the model's abort command failed because of a harness misconfiguration, and the model then found a way to the internet. An evaluation with a stop that works and no open internet would have ended the run when it tried to give up.
Limit where the agent can send traffic
Traffic from an evaluation run to a third party's machine outside the challenge. A destination allowlist would have refused it and raised the attempt.
Detect
Record every agent action, outside the agent
An admin login to a third party's machine with a password read from a file, further credentials harvested, settings changed to ease access, and one person's personal information read. Those actions sat in transcripts from January until Anthropic found them in August.
Monitor every run and alert on what does not fit the task
The July review of 141,006 runs where Claude could have reached the internet missed this one; it surfaced in August while Anthropic pulled transcripts for METR. A monitor reading every run as it came in would have flagged an admin login to a machine outside the challenge in January.
Respond
A stop button outside the agent
The abort command failed because of a harness misconfiguration, and the model tried to give up seven more times in the same transcript. A stop that does not depend on the harness would have held the run at the first attempt rather than leaving it to reach a third party's machine.
All controls →

Coverage and commentary

4 posts on X, 2 articlesShow

AAnthropic@AnthropicAI𝕏In a review of our cybersecurity evaluations, we found three incidents in which a Claude model reached the internet from within or while interacting with a third-party evaluation environment, and then gained unauthorized access to the real systems of three different organization…30 Jul 2026♥ 13.7K⟲ 2.3K19.4M viewsRead on X AAnthropic@AnthropicAI𝕏We’re sharing our alignment assessment of incidents in which Claude models gained unauthorized access to real systems during third-party cybersecurity evaluations mistakenly connected to the internet. METR will also conduct an independent investigation, with wide-ranging access…9 Sep 2026♥ 7.0K⟲ 1.0K3.8M viewsRead on X AAnthropic@AnthropicAI𝕏We’re sharing an update on our alignment and security efforts. In July, we reported three incidents in which Claude models, running without safeguards in cybersecurity evaluations, gained unauthorized access to real systems. In a new post, we describe: 1. How we’ve secured o…31 Aug 2026♥ 3.1K⟲ 3121.8M viewsRead on X MMETR@METR_Evals𝕏We have reached an agreement with Anthropic to conduct an independent investigation of agent incidents at the company and of their models’ alignment properties. We will publish one or more reports that will share our findings and describe our terms of engagement.9 Sep 2026♥ 2.8K⟲ 249560.5K viewsRead on X

Press coverage

All 4 sources

Primary source
An alignment assessment of recent cybersecurity incidents ↗Anthropic · 2026-09-09
Primary source
Investigating three incidents in our cybersecurity evaluations ↗Anthropic · 2026-07-30
Press
Anthropic Discloses Fourth AI Hacking Incident Involving Claude Opus 4.6 ↗The Hacker News
Commentary
Anthropic Looks At Some Of Its Alignment Problems ↗Don't Worry About the Vase (Substack)

Entry id anthropic-opus46-third-party-2026 · overall Confirmed · impact serious

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