# Spec: Environment Variable Protection (Process-Level Env Scrubbing) Status: Draft Owner: PMG sandbox Related: `sandbox/util/dangerous.go` (`DANGEROUS_FILES`), `docs/sandbox.md` ## 1. Background Modern software supply chain worms increasingly steal credentials from the **process environment** rather than from files on disk. The SafeDep analysis of the Miasma / Mini Shai-Hulud toolkit () documents this directly: - The payload is **TypeScript executed via Bun**, with a build-time *"Env-scramble"* transform that rewrites `process.env.GITHUB_TOKEN` into `process.env[scramble("GITHUB_TOKEN")]`, hiding the variable **names** from static analysis. It skips only `NODE_ENV` and `TZ`. - A `Provider` abstraction harvests source-specific credentials from **AWS, Azure, GCP, Kubernetes, HashiCorp Vault, and password managers (1Password, Bitwarden)**, then a `Collector` + `Sender` chain exfiltrates them. - Persistence drops a **Python** hourly C2 agent (`GITHUB_MONITOR.py`). - Exfiltration rides **GitHub commit search / commits over `github.com:443`** — the same host PMG's npm profile already allowlists — so **network egress filtering cannot stop this exfil**. The only control that breaks the kill chain is *preventing the read* in the first place. When a developer runs `pmg npm install` (or `pip`, `uv`, etc.), any malicious install hook or transitive dependency inherits PMG's full environment, including `AWS_*`, `GITHUB_TOKEN`, `NPM_TOKEN`, `TWINE_PASSWORD`, and similar. PMG already blocks credential **files** by default (`DANGEROUS_FILES`); this spec extends the same default-deny philosophy to **environment variables**. ## 2. Goals and non-goals ### Goals - Scrub a default-deny list of sensitive environment variables from the child process environment before a package manager command is executed. - Make the deny list **configurable**, mirroring `DANGEROUS_FILES`: a built-in default that profiles can extend and selectively override. - Let each sandbox **profile re-allow ecosystem-specific variables** so package managers keep working without surprise friction (e.g. npm keeps `NPM_TOKEN`). - Work on **all platforms**, since it is plain environment filtering and does not depend on OS sandbox primitives (Seatbelt / Bubblewrap / Landlock). ### Non-goals (accepted risk for v1) - **We accept that a malicious payload run by a given ecosystem can steal that ecosystem's own publishing token.** A malicious JS package executed during `npm install` can still read `NPM_TOKEN` (the npm profile re-allows it), but **not** a PyPI token or an AWS key. Symmetrically, a malicious Python package cannot read `NPM_TOKEN` or `AWS_*`. This is a deliberate trade-off: the ecosystem's own auth token must be present for the package manager to function, and removing it would break legitimate publish/auth flows. - We do **not** attempt to defeat secrets read via other channels (process memory, `/proc`, files). Those are listed under Future Enhancements. - We do **not** introduce a full default-deny-all (allowlist-only) environment in v1. That is a future, higher-friction mode (see §9). ## 3. Design overview Two layers, exactly mirroring the `DANGEROUS_FILES` model: 1. **Built-in default deny list** — `DANGEROUS_ENV_VARS` in `sandbox/util`, an explicit, curated list of **known** credential variable names (e.g. `AWS_SECRET_ACCESS_KEY`, `GITHUB_TOKEN`, `TWINE_PASSWORD`). No generic `*_TOKEN` / `*_SECRET` catch-alls live in the default — they would clip legitimate build variables for every user. The list is a precise enumeration that grows one literal name at a time. 2. **Per-profile `environment:` section** — each sandbox policy may declare additional `deny` patterns and `allow` patterns. The **matching engine supports glob wildcards**, so a profile that wants aggressive coverage can opt into it explicitly (e.g. `deny: ["*_TOKEN", "AWS_*"]`) without that risk being imposed on everyone by default. `allow` suppresses matching built-in or profile denies (allow always wins), letting each ecosystem re-permit the variables its package manager legitimately needs. Enforcement is a single chokepoint: in `executor.ApplySandbox`, after the sandbox policy is resolved **and after the project overlay and runtime `--sandbox-allow` overrides have been merged into it**, the resolved environment policy is applied to `cmd.Env`, removing denied variables before the child process is spawned. `ApplySandbox` is already the shared entry point for both the guard and proxy flows and runs before the direct and PTY launch paths, so one integration point covers every package-manager child PMG spawns — and it sits downstream of overlays and CLI overrides, so those compose for free. ``` os.Environ() -> shim.FilterPMGFromEnv() (existing: strips PMG_SHIM_PATH, ~/.pmg/bin) -> mergeEnv(overrides) (existing) -> [cmd.Env set in runner] -> executor.ApplySandbox(): resolve policy (includes environment:) applyProjectOverlay(policy, ...) (existing; now also env allow) applyRuntimeOverrides(policy, --sandbox-allow) (existing; now also env allow) cmd.Env = util.ScrubEnv(cmd.Env, policy.Environment) <-- NEW, last step apply OS sandbox -> exec child (direct / PTY / proxy) ``` ### Why enforcement is gated on sandbox being enabled To stay consistent with `DANGEROUS_FILES` (which only takes effect when the sandbox is enabled) and to honor "can be overridden by sandbox config," v1 enforces env scrubbing **only when the sandbox is enabled for the package manager**. If a profile is explicitly disabled for a PM, no scrubbing occurs — disabling the sandbox disables all of its protections, which is the existing, predictable contract. Making env scrubbing always-on regardless of sandbox state is called out as a future enhancement (§9) because it is independently valuable (it needs no OS sandbox support) but changes the current contract. ## 4. Configuration schema ### 4.1 Policy YAML (`sandbox/profiles/*.yml`) A new optional top-level `environment:` block on `SandboxPolicy`: ```yaml environment: # Extra variable-name patterns to scrub, in addition to the built-in # DANGEROUS_ENV_VARS default deny list. Case-insensitive globs are supported, # so a profile can opt into broad matching that the default list omits. deny: - MY_CUSTOM_SECRET - "*_TOKEN" # opt-in wildcard: not in the built-in default - "AWS_*" # Variable-name patterns to keep even if a built-in or profile deny would # otherwise scrub them. Allow always wins. Case-insensitive globs. allow: - NPM_TOKEN - NODE_AUTH_TOKEN - npm_config_* ``` Go types (in `sandbox/policy.go`): ```go type SandboxPolicy struct { // ... existing fields ... Environment EnvironmentPolicy `yaml:"environment" json:"environment"` } // EnvironmentPolicy controls which environment variables are scrubbed from // the child process. Deny extends the built-in DANGEROUS_ENV_VARS; Allow // suppresses matching denies (allow wins). Patterns are case-insensitive // name globs. type EnvironmentPolicy struct { Allow []string `yaml:"allow" json:"allow"` Deny []string `yaml:"deny" json:"deny"` } ``` Inheritance: `Environment.Allow` and `Environment.Deny` are unioned with the parent in `MergeWithParent` (same semantics as filesystem/network/process lists). No path expansion is needed in `ResolveProfile` (these are variable names, not paths), but the slices are deep-copied like the others. ### 4.2 `config.template.yml` Document the new section under the sandbox docs block, including the note about the accepted-risk trade-off and a pointer to this spec. No new top-level config key is required — env protection is part of the per-PM sandbox policy. ## 5. Built-in default deny list (`DANGEROUS_ENV_VARS`) Lives next to `DANGEROUS_FILES` in `sandbox/util/dangerous.go`. **The built-in list contains only explicit, known secret-bearing variable names — no generic `*_TOKEN` / `*_SECRET` style catch-alls.** Generic wildcards in the default list carry too much risk of silently clipping a legitimate build variable, and the false-positive blast radius would land on every user. We prefer a precise, auditable enumeration that we curate as new credential variables become known. Wildcards are intentionally **not** in the default list, but the **matching engine fully supports glob patterns** (see §7). Users who want broader, more aggressive coverage opt into it explicitly per profile via `environment.deny` (e.g. add `"*_TOKEN"` or `"AWS_*"` to a profile). This keeps the default safe and predictable while leaving aggressive matching one config line away for those who want it. Indicative starting set (curated; finalized in implementation review): ```go var DANGEROUS_ENV_VARS = []string{ // Cloud providers "AWS_ACCESS_KEY_ID", "AWS_SECRET_ACCESS_KEY", "AWS_SESSION_TOKEN", "AWS_SECURITY_TOKEN", "AZURE_CLIENT_SECRET", "AZURE_CLIENT_ID", "AZURE_TENANT_ID", "ARM_CLIENT_SECRET", "GOOGLE_APPLICATION_CREDENTIALS", "GCP_SERVICE_ACCOUNT_KEY", "CLOUDSDK_AUTH_ACCESS_TOKEN", "DIGITALOCEAN_ACCESS_TOKEN", // Package registry / publishing tokens "NPM_TOKEN", "NPM_AUTH_TOKEN", "NODE_AUTH_TOKEN", "NPM_CONFIG__AUTH", "TWINE_USERNAME", "TWINE_PASSWORD", "PYPI_TOKEN", "UV_PUBLISH_TOKEN", "FLIT_PASSWORD", "POETRY_PYPI_TOKEN_PYPI", "POETRY_HTTP_BASIC_PYPI_PASSWORD", "GEM_HOST_API_KEY", "CARGO_REGISTRY_TOKEN", // VCS / CI "GITHUB_TOKEN", "GH_TOKEN", "GH_ENTERPRISE_TOKEN", "GITLAB_TOKEN", "CI_JOB_TOKEN", // Secrets managers "VAULT_TOKEN", // Misc high-value "DOCKER_PASSWORD", "DOCKER_AUTH_CONFIG", "SNYK_TOKEN", "CODECOV_TOKEN", "OPENAI_API_KEY", "ANTHROPIC_API_KEY", "HUGGING_FACE_HUB_TOKEN", } ``` This list is deliberately a denylist of literal names. Adding a new known credential variable is a one-line change here; broadening to pattern matching is a per-profile opt-in, not a default. ### Protected essential variables (never scrubbed) A small hardcoded allowlist guards core process variables so a profile that opts into broad `deny` globs cannot accidentally break execution. These are never scrubbed regardless of deny patterns: ``` PATH, HOME, USER, LOGNAME, SHELL, PWD, OLDPWD, TERM, TMPDIR, TEMP, TMP, LANG, LC_*, TZ, DISPLAY, HOSTNAME, NODE_ENV ``` The built-in literal deny list does not touch these names; the protected set is the safety net for the moment a user adds a wildcard deny like `"*_TOKEN"` to a profile. ## 6. Per-profile allow lists (avoiding developer friction) Each restrictive profile gains an `environment.allow` block re-permitting only its ecosystem's legitimately required variables. This is the mechanism behind the accepted-risk trade-off in §2. - **`npm-restrictive.yml`** (npm, pnpm, yarn, bun, npx, pnpx): ```yaml environment: allow: - NPM_TOKEN - NPM_AUTH_TOKEN - NODE_AUTH_TOKEN - npm_config_* # npm lowercases config-derived vars - NPM_CONFIG_* - NODE_EXTRA_CA_CERTS ``` Result: a malicious JS install hook can read `NPM_TOKEN`, but `AWS_*`, `TWINE_*`/PyPI tokens, `GITHUB_TOKEN`, and `VAULT_*` remain scrubbed. - **`pypi-restrictive.yml`** (pip, uv, ...): ```yaml environment: allow: - TWINE_USERNAME - TWINE_PASSWORD - TWINE_REPOSITORY* - PIP_* - UV_* - POETRY_* ``` Result: a malicious Python package can read its PyPI publishing creds, but not `NPM_TOKEN` or `AWS_*`. - **`pnpm-restrictive.yml`**: same allow set as npm. - **`npx.yml`**: npm allow set (npx executes npm-ecosystem code). Each profile's allow list should be reviewed so it grants the **minimum** set of variables the package manager needs for auth, registry config, and TLS. ## 7. Runtime overrides (`--sandbox-allow`) and project overlays Every other resource type (read, write, exec, net-connect, net-bind) is tunable three ways that all converge on the resolved policy: the profile YAML, a one-off CLI `--sandbox-allow type=value`, and a persisted per-repo overlay (`pmg sandbox allow`, stored under `SandboxOverlayDir()`). Environment protection must be consistent with this model, otherwise a developer who hits a scrubbed variable would have no escape hatch short of editing a profile file. ### 7.1 New allow type: `env` Add `SandboxAllowEnv SandboxAllowType = "env"` to the existing enum in `config/config.go`, so users can write: ```bash pmg --sandbox-allow env=NPM_TOKEN npm install # one-off pmg sandbox allow env=NPM_TOKEN # persist for this repo ``` - `config/sandbox_allow.go` (`parseSingleOverride`) accepts the `env` type. **Crucially, the value is taken literally as a variable-name pattern and is NOT path-resolved or host:port-parsed** the way `read`/`write`/`net-*` values are. An `env` value is a name or glob (e.g. `NPM_TOKEN`, `npm_config_*`). - `sandbox/executor/apply.go` (`applyRuntimeOverrides`) gains an `env` case that appends the value to `policy.Environment.Allow`: ```go case config.SandboxAllowEnv: log.Infof("Sandbox override: allowing environment variable %s", override.Value) policy.Environment.Allow = append(policy.Environment.Allow, override.Value) ``` Unlike the filesystem cases, there is **no `removeExactMatch` on a deny list**: env uses allow-wins semantics (§8), so appending to `Allow` is sufficient to un-scrub a variable regardless of whether it was denied by the built-in list or a profile `deny` glob. This is simpler than — and intentionally different from — the filesystem model, where deny shadows allow and so an exact deny entry must be removed. ### 7.2 Overlays Overlays already persist generic `OverlayAllow{Type, Value}` entries and replay them through `applyRuntimeOverrides` via `ToAllowOverrides()`. Once `env` is a valid allow type, overlays carry env allowances with **no overlay schema change** (`OverlaySchemaVersion` stays 1) — `pmg sandbox allow env=NPM_TOKEN` writes an `env` entry that is applied on every run in that repo. The overlay `Value` is stored and replayed verbatim, which is correct here precisely because env values are not path-normalized. ### 7.3 Allow-only, and governed by lockdown - Overrides and overlays are **allow-only** by design (they widen access). There is deliberately no `--sandbox-allow`/overlay form that *adds* a deny; tightening is done in the profile `environment.deny`. This matches every existing type. - The `env` allow override is **security-sensitive** (it re-exposes a credential), so it inherits the existing governance unchanged: `--sandbox-allow` is already a managed/governed flag, so under `global_lockdown` a CLI `env=` allow is refused, and `applyProjectOverlay` already ignores overlays when `cfg.IsLocked()`. A locked managed baseline can therefore **forbid un-scrubbing** a variable, which is the desired property for centrally managed fleets. No additional governance code is needed; the spec only requires that the new type flow through these existing checks (covered by tests in §10). ### 7.4 No violation-driven auto-suggestion The `read`/`write`/`exec` flows can suggest an override after a sandbox *violation* (`BuildAllOverrides` / `overrideSuggestion`). Env scrubbing produces **no such violation**: the variable is simply absent, and the child may later fail for an unrelated-looking reason (e.g. "npm ERR! 401 Unauthorized"). We do **not** fabricate a synthetic violation for env. Instead, discoverability comes from audit logging (§9): the scrubbed variable **names** are logged, so a user who sees an auth failure can find the "scrubbed NPM_TOKEN" line and run `--sandbox-allow env=NPM_TOKEN`. The docs (`docs/sandbox.md`) must spell out this remediation explicitly since there is no automatic suggestion. ## 8. Matching semantics - Matching is on the variable **name** (the substring left of the first `=` in each `KEY=VALUE` entry). - Patterns are **case-insensitive** globs (reuse `sandbox/util` glob matching; Miasma-style scrambling targets conventionally uppercase names, but case-insensitivity removes a trivial bypass and matches lowercase `npm_config_*`). - An entry is **scrubbed** (removed entirely, not blanked) iff: `matches(effectiveDeny) AND NOT matches(allow) AND NOT isProtectedEssential`. - `effectiveDeny = DANGEROUS_ENV_VARS ∪ policy.Environment.Deny` (the latter already merged from inheritance; deny is profile-only — overlays/CLI cannot add denies, see §7.3). - `allow = policy.Environment.Allow`, which by the time `ScrubEnv` runs already includes profile allows **plus** any overlay and `--sandbox-allow env=` entries merged in by `applyProjectOverlay` / `applyRuntimeOverrides`. **Allow wins over deny** (built-in or profile). - Removal (vs. setting empty) is intentional: absence is the cleanest "not set" signal and avoids tools that treat empty-string specially. ### Proposed API (in `sandbox/util`) ```go type EnvScrubOptions struct { Allow []string // profile environment.allow (already merged) Deny []string // profile environment.deny (already merged) } type EnvScrubResult struct { Env []string // kept entries (KEY=VALUE) Removed []string // removed variable NAMES only (never values), for audit } // ScrubEnv removes sensitive variables from env per the built-in // DANGEROUS_ENV_VARS list extended by opts.Deny and suppressed by opts.Allow. func ScrubEnv(env []string, opts EnvScrubOptions) EnvScrubResult ``` This parallels `GetMandatoryDenyPatterns` and keeps all matching logic in `sandbox/util` where `DANGEROUS_FILES` already lives, so the linter and tests have a single source of truth. ## 9. Audit and observability - `ScrubEnv` returns the **names** of removed variables (never values). - `executor.ApplySandbox` logs the scrubbed count at info and the names at debug, and threads them into the existing sandbox `ExecutionResult` so they can be surfaced in the event log alongside other sandbox decisions. - Emitting "credential variable present and scrubbed during install" into the eventlog gives defenders a signal that a package run had access to (and was denied) sensitive variables — useful even when nothing malicious is observed. ## 10. Testing - `sandbox/util`: table-driven tests for `ScrubEnv` covering deny match, allow suppression, protected-essential preservation, case-insensitivity, profile glob denies, and removal-vs-blank. Use `testify` `assert`/`require` per repo conventions. - `sandbox/policy_test.go`: `Environment` merge under inheritance (union of allow/deny, parent + child). - `executor`: env is scrubbed when sandbox enabled; untouched when the policy is disabled for the PM; PTY and direct paths both receive the scrubbed slice. - Profile fixtures: assert npm profile keeps `NPM_TOKEN` and drops `AWS_*` / `TWINE_PASSWORD`; pypi profile keeps `TWINE_*` and drops `NPM_TOKEN` / `AWS_*` (encodes the §2 accepted-risk contract as a regression test). - **Override parsing** (`config/sandbox_allow_test.go`): `env=NPM_TOKEN` parses to `SandboxAllowEnv` with the value kept verbatim (no path resolution); a glob value like `env=npm_config_*` is preserved. - **Override application** (`sandbox/executor`): `--sandbox-allow env=AWS_PROFILE` un-scrubs an otherwise-denied variable; allow-wins holds even against a profile `deny` glob. - **Overlay round-trip**: an `env` allow saved to an overlay is replayed on the next run and un-scrubs the variable, with `OverlaySchemaVersion` unchanged. - **Governance**: under `global_lockdown`, a CLI `--sandbox-allow env=` is refused and an overlay `env` entry is ignored, so a locked baseline keeps the variable scrubbed. ## 11. Rollout / compatibility - Backward compatible: profiles without an `environment:` block still get the built-in `DANGEROUS_ENV_VARS` default deny once sandbox is enabled. Existing configs need no change. - The built-in deny list is literal known names only, so false positives are unlikely. If a niche build step relied on one of those exact names, the escape hatches are the per-PM `environment.allow`, a one-off `--sandbox-allow env=NAME`, or a persisted overlay — all surfaced by the audit log of scrubbed names so the cause is obvious. - Document in `docs/sandbox.md`: the default deny list, the per-profile allow mechanism, the `--sandbox-allow env=` / `pmg sandbox allow env=` escape hatch and its remediation message, and the accepted-risk trade-off. ## 12. Future enhancements Captured from the broader analysis; out of scope for v1 but natural follow-ups. 1. **Always-on (sandbox-independent) enforcement.** Scrub env even when the OS sandbox is unavailable or disabled, since env filtering needs no platform primitive. Highest-value extension; deferred only to avoid changing the current "sandbox off = no protection" contract without explicit opt-in. 2. **Default-deny-all (allowlist-only) env mode.** An opt-in strict tier (`environment.default_deny: true`) that starts from an empty environment and passes only an allowlist (`PATH`, `HOME`, `npm_config_*`, proxy/CA vars, ...), implemented via `--clearenv`/`--setenv` on Linux. Best suited to CI, where the environment is narrow and knowable. Strongest defense against novel variable names but higher friction. 3. **Linux `/proc` hardening.** The Miasma worm dumps GitHub Actions runner memory via `/proc` to obtain "secrets not exposed as env vars." Pair env scrubbing with PID-namespace isolation (already `unsharePID: true`) plus masking other processes' `environ`/`mem` (e.g. `hidepid`/minimal proc mount) so scrubbing cannot be sidestepped through `/proc`. 4. **Sandbox-detection hardening.** Miasma fingerprints analysis environments via known fake env vars; ensure PMG does not inject identifiable markers into the child environment that aid evasion. 5. **Audit-only mode.** A non-enforcing mode that logs which sensitive variables *would* be scrubbed, to size impact before turning enforcement on. 6. **Egress note (defense-in-depth only).** Network allow/deny is explicitly *not* a primary control for this threat because exfil rides allowlisted `github.com`; keep it as layered defense, not a substitute for scrubbing.