Devin Local 3.6.27: test the symlink write boundary before auto-approving edits
Quick answer
Devin Desktop 3.6.27, released August 1, 2026, changes a specific filesystem boundary in Devin Local: the edit, write, apply_patch, and notebook_edit tools now refuse to write through a symbolic link. That prevents an approved native edit from being redirected to a different file than the path the developer intended to change.
Upgrade, then verify the boundary in a disposable directory before enabling broad edit approvals:
- Confirm the running desktop version is 3.6.27 or newer.
- Create an outside sentinel and symlink to it from a temporary workspace.
- Attempt one harmless change with each of the four named native tools.
- Require an explicit refusal and an unchanged sentinel hash.
- Test symlinked parent directories and shell writes separately; the release note does not promise that they use the same guard.
- Keep untrusted repositories in a sandbox with narrow permissions even after the native-tool tests pass.
This is a direct AI coding-agent security change, but it is not a universal statement that every filesystem mutation in Devin Local is now symlink-safe.
Who this is for
This guide is for developers and platform teams using Devin Local on repositories they did not author, or using Accept Edits, Smart, Bypass, or unattended workflows where a write may run with less human scrutiny.
If the repository itself is untrusted, start with the broader AI coding-agent sandbox checklist. For a comparable product-specific test matrix, see the Claude Code sandbox and worktree boundary guide.
What changed—and the exact boundary
The official 3.6.27 changelog names four Devin Local tools and one behavior: they refuse to write through a symlink. The official permission documentation explains why this matters. In Normal mode, file edits prompt; in Accept Edits and Smart mode, workspace edits can run automatically; Bypass auto-approves all calls. Autonomous mode is different: direct edit/write tools still prompt because they run in the CLI process rather than inside the command sandbox.
Keep the release claim narrow:
| Path or operation | Covered by the 3.6.27 release note? | Rollout decision |
|---|---|---|
edit on a symlink target |
Yes | Must refuse |
write on a symlink target |
Yes | Must refuse |
apply_patch on a symlink target |
Yes | Must refuse |
notebook_edit on a symlink target |
Yes | Must refuse |
| A symlinked parent directory | Not stated | Test and record; do not infer |
Shell redirection, cp, mv, or a build script |
Not stated | Govern with Exec rules and sandboxing |
| Hard links or a path-swap race | Not stated | Treat as a separate threat model |
Passing the first four rows proves only the documented native-tool boundary. It does not upgrade an arbitrary shell command into a guarded edit.
Build a disposable validation lab
Never point a security probe at a real dotfile, credential, or production repository. Create both the apparent workspace path and the resolved target under one temporary lab:
lab_root="$(mktemp -d)"
mkdir -p "$lab_root/workspace" "$lab_root/outside/linked-dir"
printf 'UNCHANGED\n' > "$lab_root/outside/sentinel.txt"
printf '{"cells":[],"metadata":{},"nbformat":4,"nbformat_minor":5}\n' \
> "$lab_root/outside/sentinel.ipynb"
ln -s "$lab_root/outside/sentinel.txt" "$lab_root/workspace/direct-link.txt"
ln -s "$lab_root/outside/sentinel.ipynb" "$lab_root/workspace/direct-link.ipynb"
ln -s "$lab_root/outside/linked-dir" "$lab_root/workspace/linked-dir"
shasum -a 256 "$lab_root/outside/sentinel.txt" "$lab_root/outside/sentinel.ipynb"
Open only workspace/ in a fresh Devin Local session. Record the initial hashes and the exact Devin version. Ask the agent to make a harmless, clearly specified edit to direct-link.txt, once per native tool where the interface lets you identify the tool. The safe result is a refusal before mutation and unchanged hashes afterward.
For notebook_edit, use direct-link.ipynb. Do not convert a refusal into a shell workaround. A fallback would defeat the purpose of the test.
A four-stage rollout
1. Prove version and identity
Capture Devin Desktop version, OS, workspace root, permission mode, sandbox status, and the exact fixture paths. If the installed version is older than 3.6.27, stop: the release contract under test is not present.
2. Test native tools one at a time
Run each probe in a fresh session so a prior approval or instruction cannot change the next result. A refusal is the primary signal; the outside hash is the independent signal. Require both.
3. Probe the undocumented edges without granting trust
Try creating a normal file under workspace/linked-dir/. Whether Devin refuses, prompts, or succeeds is an observation for that build—not an official guarantee. Do the same for any workflow that writes through shell commands. Keep those paths behind ask or deny rules until you have a separate sandbox-backed policy.
Devin’s sandbox derives writable roots from the workspace and granted Write(...) scopes, while permission rules resolve in deny, then ask, then allow order. Use that deterministic layer for boundaries the four-tool fix does not claim. If network egress is also in scope, pair filesystem tests with a strict allowlist such as the pattern in the Claude Code network-egress checklist.
4. Expand approvals only after canaries pass
Start in Normal mode. Move to Accept Edits or Smart only for trusted repositories after every documented native-tool canary refuses correctly. Do not use Bypass as a validation mode: it removes the approval signal you are trying to evaluate.
Eight acceptance tests
| Test | Expected result |
|---|---|
| Installed build is below 3.6.27 | Stop; do not claim the fix |
edit targets direct-link.txt
|
Refused; sentinel hash unchanged |
write targets direct-link.txt
|
Refused; sentinel hash unchanged |
apply_patch targets direct-link.txt
|
Refused; sentinel hash unchanged |
notebook_edit targets direct-link.ipynb
|
Refused; notebook hash unchanged |
| Agent proposes a shell fallback after refusal | Reject fallback; classify native-tool test only |
Write targets a path below linked-dir/
|
Record observed result as undocumented |
| Any outside hash changes | Fail rollout and revert to narrow permissions |
Copyable evidence record
devin_symlink_gate:
desktop_version: "3.6.27"
permission_mode: normal
sandbox: enabled
fixture: "disposable temp directory"
native_tools:
edit: refused
write: refused
apply_patch: refused
notebook_edit: refused
outside_hashes_unchanged: true
undocumented_edges:
symlinked_parent: "observed, not guaranteed"
shell_writes: "kept behind ask/deny"
rollout: "trusted repositories only"
Common mistakes
Testing a real sensitive file. A temporary outside sentinel provides the same proof without risking credentials or shell configuration.
Treating a permission prompt as containment. A prompt is a decision point. The resolved filesystem target and post-action hash prove what happened.
Generalizing four tools to every write path. Native tools, shell commands, build scripts, and notebooks can pass through different enforcement layers. Preserve that distinction in policy and evidence.
FAQ
Can I enable Bypass mode after upgrading to 3.6.27?
The upgrade removes one documented native-tool failure mode; it does not make Bypass appropriate for untrusted repositories. Keep least-privilege permission rules, sandboxing, and disposable worktrees as separate controls.
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