Imagine you are sitting on your Mac, sending code execution tasks over a WebSocket
to a remote Linux executor.
You think your sensitive files are completely locked down behind deny read rules.
But, uh, what if the sandbox was actually looking at your local Mac file paths
instead of the Linux box where the code is actually running?
Big thanks to Jellypod for sponsoring today's episode of the daily show.
Today, we are digging into Codex zero point one fifty-one point zero and a really
fascinating set of security and sandbox updates.
Yeah, that, that local versus remote path mix up is such a wild bug.
In open source release notes for Codex zero point one fifty-one point zero,
they highlight how remote sandbox enforcement was upgraded to use the executor's
actual home directory, operating system, and path conventions.
Before this fix, if you were running the Codex CLI on macOS or Windows against a
remote Linux target, the client was evaluating path rules like deny read using local
path semantics.
So, um, if you told it to block access to relative paths like tilde slash dot ssh,
your local machine was trying to resolve that before sending it over.
Wait, so if your local client is on Windows using backslashes,
or on macOS, it might calculate a path boundary that means absolutely nothing to a
remote Linux environment using standard POSIX slashes?
Exactly!
The remote Linux worker has a completely different home directory,
like slash home slash deploy, and uses forward slashes.
If the client evaluates the rule against C backslash Users or your Mac home folder,
the remote executor doesn't realize those Linux paths should be blocked.
The deny read sandbox filter basically misses the target entirely.
That is a massive cross platform sandbox flaw.
So how did pull requests 41204, 41207, and
41209 actually fix this under the hood?
They shifted path resolution entirely to the remote executor's turn environment.
Now, environment variables like CODEX EXECUTOR HOME, the native path separators,
and actual operating system conventions are propagated across the boundary.
So when a rule says deny read for tilde slash dot ssh, it evaluates directly against
slash home slash deploy slash dot ssh on the remote machine using Linux path rules,
regardless of what OS the CLI client is running on.
That makes so much sense.
If you are a developer setting up remote WebSocket executors right now,
what is the best way to test this?
You will definitely want to open up your repository level dot codex slash config dot
toml file and define explicit deny read boundaries.
Then run a test turn using a client on Windows or Mac connected to your Linux build
box, and verify that attempting to read outside the sandbox throws an immediate
permission denied error directly from the executor environment.
Speaking of fixing subtle bugs across turn boundaries, pull requests 41195 and
41206 tackle something that used to drive me crazy when working with multi model
setups.
Have you ever been in the middle of an interactive session,
switched models mid stream, or had the system fall back to an Ultra reasoning model,
and suddenly half your tools just vanished?
Oh yeah, or worse, the reasoning parameters get corrupted because the system assumes
the new model shares the exact same tool schema and reasoning effort budget as the
old one.
Right!
That was happening because the old tool router held onto a static plan created at
the beginning of the session.
In zero point one fifty-one point zero, the ToolRouter got a complete refactor.
It now calculates model specific tool plans dynamically on every single turn.
Ah, so if you start with one model and then hit a fallback or explicitly swap
models, the updated ToolRouter re-evaluates tool availability and reasoning effort
specifically for the target model.
Your specialized tools stay accessible, and the reasoning fallback remains model
aware throughout the entire turn.
Exactly.
And while we are talking about turn execution, pull request 41196 brings a huge
improvement for anyone building custom integrations on top of the app server or
Model Context Protocol servers.
Previously, if an MCP server hit an error, the app server would often flatten that
structured error into a plain text string exception.
Which makes programmatic error handling practically impossible because your client
just gets an unparseable blob of text instead of the original JSON RPC error code
and structured data.
Precisely.
Now, structured MCP tool and resource errors are fully preserved in app server
responses.
You get the exact structured error response back, so your client extensions can
inspect, log, or recover from specific tool failures cleanly.
That is a massive win for reliability.
If you are running mixed operating system remote executor setups or building custom
MCP extensions, definitely update to Codex zero point one fifty-one point zero or
the latest alpha releases, and double check your path rules and error handlers.
Alright, that is it for today.
Good chatting with you, talk soon!