Mistral Vibe Fixes World-Readable Session Log Files
Mistral VibeMistral Vibe fixed a local file-permissions gap in v2.25.3: newly created session log files were previously readable by other users on the same POSIX machine, and are now restricted to the owning user. Session logs can capture prompts, file contents, and command output, so on a shared or multi-user machine the fix closes a real path for one account to read another's agent activity. It ships alongside the new /branch command and Git-aware @ file mentions in the same release.
Key Takeaways
- Session logs are now owner-only, no longer readable by other local accounts on POSIX systems once created in v2.25.3.
- Logs can hold sensitive content, including prompts, file contents, and shell command output from an agent session.
- Shared machines were exposed, since any other local user on the same box could previously open another account's session log.
- A genuine isolation fix, closing a cross-account read path rather than tweaking cosmetics or performance.
- Ships in the same release as
/branch, Mistral Vibe's v2.25.3, dated September 11, 2026. - No configuration required, the fix applies automatically to newly created session logs without an opt-in setting.
What Changed
Mistral Vibe tightened file permissions on session logs in version 2.25.3. New session log files are no longer readable by other users on POSIX systems, closing a gap where a local log file created by one account could previously be opened by any other account on the same machine.
Why It Matters
A Mistral Vibe session log is not a trivial artifact. It can capture the prompts a developer sent, the contents of files the agent read or edited, and the output of shell commands run during the session, any of which might include source code, credentials referenced in a command, or other sensitive material. On a shared development server, a CI runner with multiple service accounts, or any machine with more than one local user, a world-readable log file meant that session content was effectively visible to anyone else with a shell on that box, regardless of whether they were ever meant to see it.
A Trust-Boundary Fix, Not Polish
This falls squarely into the category of isolation fixes rather than routine cleanup: it is about who can read data across account boundaries on the same machine, not a cosmetic or performance change. Mistral Vibe did not describe the previous behavior as configurable or intentional, which suggests session logs had simply inherited default file permissions rather than being deliberately scoped to their owner from the start.