Celesto (formerly SmolVM) vs Microsoft Execution Containers

Celesto (formerly SmolVM) 52

Framework reading for local software. No credential is needed for local use, and the local API server and dashboard each require a bearer token, and cloud keys carry named permissions (22 of 30). Each computer has its own guest kernel, browser and display access uses capability URLs with a read-only option, and raw VNC is off. Against that, outbound networking is open by default and the restricting modes are opt-in (12 of 20). The security doc warns against giving connection URLs to a model as page content, but there is no guidance on treating command or page output as untrusted (5 of 15). computer logs shows startup output, with no audit log of commands (5 of 15). SECURITY.md with GitHub private vulnerability reporting and a supported-versions table, Security sections in the changelog, no security.txt, bug bounty or certification (8 of 20). Total 52.

Microsoft Execution Containers 69

No credentials to issue or leak, because the library runs in the caller's process, so the middle band (20 of 30). Least privilege is the product's job. Egress, ingress and host loopback default to deny, filesystem access is limited to listed paths, UI access is denied when omitted, and validation rejects a policy the chosen backend can't enforce. The limits are documented. isolation_session cannot restrict networking, proxy routing is cooperative on Seatbelt and WSLC, the Windows DACL fallback that edits host file permissions is allowed by default, and --audit turns the sandbox off (17 of 20). The workload's output is untrusted content. The SDK keeps warnings and denial metadata out of stdout and stderr, but we found no guidance for an agent reading that output (8 of 15). Local JSON audit records for process exits, tier fallbacks, teardown and rejected configs through --log-file on the executors, and the deny-and-record capture. We found no equivalent switch documented for the in-process SDKs (10 of 15). SECURITY.md sends reports to MSRC, CodeQL runs in CI and the repository has a fuzzing pipeline. OSV lists no advisories for the npm, crates.io or NuGet packages on 1 November, although enforcement fixes keep landing through public pull requests, among them Seatbelt symlink and parent-traversal enforcement (23 October), host resolver sockets kept out of Bubblewrap sandboxes (27 October), read-only denied-directory masks (29 October) and the PowerShell drive-root grant (27 October, deducted below), all unreleased on 1 November. The security.txt on microsoft.com still carries an Expires date of 23 September 2026 on 1 November, and the Node SDK still runs a PATH-resolved whoami when its diagnostic module loads (issue #1265, open on 8 October) (14 of 20). 20+17+8+10+14 = 69.

Celesto (formerly SmolVM) 66

Read with the local-software lines, because the graded surface runs on the owner's machine. Installs from PyPI as celesto with Python 3.11 or newer on Linux and macOS stated, plus an install script (20). The repository has pytest, e2e, lint, TypeScript and smoke-test workflows and 38 test packages, but GitHub's API answered with a rate limit, so no run result was read (15 of 25, unchecked). 22 open issues and pull requests against about 188 commits in 90 days. The open bugs include a snapshot restore that can lose a VM's disk if interrupted and a thread-safety issue with five replies (18 of 25). A dated changelog with Security, Fixed, Added and Removed sections, and the rename to Celesto marked as a breaking release, though versions stay below 1.0 (13 of 15). Pre-1.0 per SECURITY.md (0). Total 66.

Microsoft Execution Containers 81

Read with the local-software lines, because MXC is a library the owner runs. Official packages on npm, NuGet and crates.io. Node.js 24 or later is stated and Windows 11 builds are listed per release, but the README gives no minimum host version for Linux or macOS (18 of 20). The Build workflow runs lint, Windows, Linux and macOS builds and SDK unit and integration tests on every push to main. Of the last 14 completed runs on main, 10 passed and 4 failed, and the newest (7 October 2026) passed, per the 8 October check, not re-read on 1 November because GitHub's web pages refused our reader. 47 commits on main from 17 to 30 October include CI fixes for nightly test failures (18 of 25). 38 open issues against 261 closed, ten of them labelled bug, and three outside reports from 24 September to 2 October with no reply, per the 8 October check, not re-read on 1 November (19 of 25). The changelogs follow Keep a Changelog with breaking changes marked, and the v1.0.0 release notes have a breaking-changes section. The Node and .NET changelogs still list the V1 changes under Unreleased on 1 November, with no 1.0.0 or 1.0.1 heading although 1.0.1 shipped on 17 October (11 of 15). Version 1.0.0, which the release notes call the first stable release, was published on 6 October 2026 and 1.0.1 on 17 October, and three backends are marked experimental (15). 18+18+19+11+15 = 81.

Celesto (formerly SmolVM) 70

Apache-2.0 in LICENSE and on PyPI (30). The privacy policy of 30 October 2026 links a subprocessor registry and describes the CLI telemetry in the same terms as the docs, but gives no retention periods beyond as long as necessary. Stopped cloud disks are kept 30 days per the pricing page (18 of 30). The changelog marks removals and the breaking rename, and the glossary lists older names still accepted, with no written deprecation policy (10 of 20). Telemetry is disclosed in the README, CLI reference and privacy policy, with three opt-outs, but it is on by default after the notice (16 of 20). Total 74.

Microsoft Execution Containers 84

MIT for the repository and for the published npm package, whose LICENSE.md we compared with the repository's (30). Local software with no service behind it. The telemetry docs list what the optional Windows events contain (version, backend, bounded outcomes, policy fingerprints) and what they omit (commands, file paths, credentials, free-form error text), and the consent prompt links Microsoft's privacy statement. No retention period for those events is stated (24 of 30). The release notes name V1 as the compatibility boundary for 1.x under semver 2.0, breaking changes need a new versioned surface, and the schema docs mark retired contracts. No notice period with dates was found (12 of 20). Telemetry is disclosed in the README, off by default, opt-in for each run, subject to user consent and an administrative block, and absent on Linux and macOS (20). 30+24+12+20 = 86.

Celesto (formerly SmolVM) 81

0.1.13 on PyPI on 5 November 2026, tagged 6 November (30). 22 PyPI releases in the 90 days to 6 November (20). Most open issues are filed by maintainers. Outside reports such as the thread-safety issue got replies, and several recent ones have none yet; pull-request reply times were not read (15 of 25). The Python SDK is current, the TypeScript SDK is an alpha not published to npm (8 of 15). uv and Cargo lock files, CodeQL and publish workflows, with run results unread (8 of 10). Total 81.

Microsoft Execution Containers 92

v1.0.1 on npm and crates.io on 17 October 2026, 15 days before the check, still the newest release on 1 November (30). Four npm releases in the 90 days from 3 August, 0.8.0 on 22 August, 0.9.0 on 28 September, 1.0.0 on 6 October and 1.0.1 on 17 October (the npm dates per the 17 October check, crates.io and the tags re-read on 1 November) (20). 261 issues closed against 38 open, with issue forms, triage labels and fixes that land within days, and three outside bug reports filed between 24 September and 2 October with no comment, per the 8 October check, not re-read on 1 November (19 of 25). Official SDKs for Node.js, .NET and Rust, all at 1.0.1 (15). A package-lock check, CodeQL and Dependabot in CI, with 47 commits on main from 17 to 30 October. The npm package has no repository field and no provenance attestation, per the 17 October check (8 of 10). 30+20+19+15+8 = 92.

Celesto (formerly SmolVM) 69

A CLI and SDK add no tool definitions to an agent's context. Collected command output is capped at 8 MiB with streaming as the alternative (18 of 25). computer list, logs --follow and name lookups, with little filtering (10 of 20). JSON errors carry a recovery command where Celesto has one, and cloud errors carry stable codes, operation and computer context and recovery fields since 0.1.7 (18 of 20). State-changing cloud requests are never replayed automatically and computers are addressed by unique names, but there are no idempotency keys (10 of 20). with Computer() creates and deletes a computer with no parameters, with Python and an alpha TypeScript SDK (13 of 15). Total 69.

Microsoft Execution Containers 74

One request type with command as the only required field, and run returns stdout, stderr, the exit code, a timeout flag and warnings. We found no documented cap on captured output, and the npm package is a 37.7 MB tarball (18 of 25). spawn streams output and timeoutMs bounds a run, but there is no truncation or size control on captured output (10 of 20). MxcError carries one of 12 codes with optional operation, native code and remediation, and a deny-and-record mode lists blocked accesses on ProcessContainer (18 of 20). validate* calls dry-run every lifecycle step, and lifecycle state errors are typed (already_started, stale_id). Issue #1429, open since 6 October, reports a second deprovision returning success, per the 8 October check, not re-read on 17 October. Not an MCP server, so no tool annotations apply (13 of 20). Network, filesystem and UI policy default to deny, and official SDKs exist for Node.js, .NET and Rust (15). 18+10+18+13+15 = 74.