Supply Chain Hardening Skill for Claude

Supply-chain hardening

Defends a journalism toolchain against the dominant npm/bun supply-chain attack pattern: a maintainer account or CI pipeline is compromised, a malicious version ships, and machines install it before anyone notices. Recent example: the Mini Shai-Hulud TanStack attack (2026-05-11) compromised 84 versions across 42 @tanstack/* packages and exfiltrated AWS / GCP / Vault / GitHub / SSH credentials via a postinstall script.

The defense is layered and intentionally simple:

• Install-time cooldown — only install package versions older than N days (default 7). This is the primary defense. By the time the cooldown expires, the security community has almost always flagged a compromised version and the registry has yanked it.
• Sandboxed pre-install scan — when the cooldown has to be bypassed (CVE patch, fresh dep, urgent install), run the candidate tarball through a static-analysis scan that looks for the diagnostic signatures of supply-chain malware. The scan runs inside bwrap/firejail/unshare so a malicious package can't escape the inspection.
• --ignore-scripts at install — postinstall is the #1 attack vector. Skip lifecycle scripts on every cooldown-bypass install.

These three together would have blocked the Mini Shai-Hulud TanStack attack on a stock laptop with no human in the loop.

Configure the cooldown

Verified config keys (npm v11+ and bun 1.3+):

| Manager | File | Key | Units | Exclusion key |

|---|---|---|---|---|

| npm | ~/.npmrc (or project .npmrc) | min-release-age | days | none yet — proposed in npm/cli#8994 |

| bun | ~/.bunfig.toml (or project bunfig.toml) | [install] minimumReleaseAge | seconds | [install] minimumReleaseAgeExcludes = [] (exact names, no globs) |

Minimal config:

# ~/.npmrc
min-release-age=7

# ~/.bunfig.toml
[install]
minimumReleaseAge = 604800  # 7 days
minimumReleaseAgeExcludes = []

Requires npm 11+. Older npm silently ignores unknown keys, so the config looks correct but does nothing. Check with npm --version and npm config get min-release-age (should echo 7, not null).

Per-command bypass

When the cooldown blocks an install you actually want:

npm install <pkg>@<version> --min-release-age=0 --ignore-scripts
bun add     <pkg>@<version> --minimum-release-age=0 --ignore-scripts

The bun add --minimum-release-age=0 CLI flag works in 1.3+ even though the docs don't list it — it follows bun's bunfig key → kebab-case flag convention.

Always pair the bypass with --ignore-scripts. Postinstall is the most common payload-execution path in supply-chain malware (Mini Shai-Hulud, event-stream, ua-parser-js, coa, all used it). Native modules that legitimately need postinstall can have the script run manually after a human-readable review:

(cd node_modules/<pkg> && cat package.json | jq .scripts) # eyeball it
(cd node_modules/<pkg> && npm run postinstall)            # run if it checks out

When to scan before bypassing

The scan is for the dangerous moment: you've decided to bypass the cooldown and need a sanity check. The skill ships a reference script (scripts/hotpatch.example.sh) implementing the heuristics. Adapt it to your machine — Bash assumes bwrap (Linux); macOS users substitute sandbox-exec or skip the sandbox layer with the trade-off documented.

Static checks the scan should perform (each backed by a real attack):

| Check | Diagnostic of | Severity |

|---|---|---|

| optionalDependencies / dependencies containing github: or git+ URLs | Mini Shai-Hulud (delivered payload via github:tanstack/router#<sha> ref) | RED |

| Large JS file at package root not referenced by main/module/exports/bin/files | Planted payload pattern (router_init.js in Mini Shai-Hulud) | RED |

| Unpacked size >3x the prior stable version | Bulk payload smuggling | RED |

| fileCount delta of 1–4 paired with >2x size jump | Single planted file | RED |

| preinstall/install/postinstall/prepare scripts present | Lifecycle-script attack vector (event-stream, ua-parser-js, etc.) | YELLOW |

| JS files referencing .ssh/, .aws/, .npmrc, GITHUB_TOKEN, AWS_SECRET, kube config | Credential exfiltration | YELLOW |

| Version flagged deprecated in npm registry with "security"/"compromised"/"malicious" wording | Maintainer/registry yank | RED |

| OSV.dev returns known vulnerabilities for <pkg>@<version> | Disclosed CVE | RED (severity-dependent) |

Why prerelease versions are skipped from the size-delta baseline: dev/beta/rc versions have wildly different sizes than stable releases and produce false positives.

What the cooldown does *not* catch

Be honest about the limits with whoever you're configuring this for:

• Old packages with new malicious versions still in the cooldown window are blocked, but if the bad version *also* passes the cooldown (rare but possible — a compromise that goes >7 days undetected), the cooldown alone won't help. The scan catches most of those.
• Transitive deps. A clean <pkg> you install can pull in a compromised transitive. Defenses: scan against the *resolved* tree (npm audit, osv-scanner), and keep the cooldown active globally so transitive resolution also waits.
• npm ci against an existing lockfile. The cooldown applies during *resolution*, not installation of already-pinned versions. If your lockfile pins a compromised version, npm ci will install it. Mitigation: scan lockfiles in CI with osv-scanner --lockfile=package-lock.json.
• Pre-existing compromised packages in node_modules. Hardening protects future installs, not past ones. Audit existing deps separately (npm audit, osv-scanner, manual review of recently-published deps in your tree).

Quick-start workflow for a new machine

• Verify npm >= 11: npm --version. If older, upgrade (sudo npm i -g npm@latest or tarball-swap if self-upgrade races).
• Write ~/.npmrc and ~/.bunfig.toml with the config above.
• Verify: npm config get min-release-age returns 7. cat ~/.bunfig.toml shows the [install] block.
• Copy scripts/hotpatch.example.sh to ~/.claude/hotpatch.sh (or wherever fits). Make executable. Run ./hotpatch.sh --self-test against the synthetic Mini Shai-Hulud fixture (also shipped) to confirm the heuristics fire.
• Document the bypass workflow somewhere your team will find it. The whole skill assumes the bypass is *rare* and *reviewed*, not the default.

Threat model: what this defends and what it doesn't

| Defends against | Doesn't defend against |

|---|---|

| Maintainer account compromise (npm token theft) | Targeted attack tailored to wait through the cooldown |

| CI/CD pipeline hijack (Mini Shai-Hulud, valid OIDC tokens, SLSA-attested malice) | Compromise of a transitive dep already pinned in a lockfile |

| Typosquatting (lookalike package names) — when paired with npm pkg fix and lockfile review | Malicious code in your own dev dependencies that you authored |

| Postinstall payload execution (cooldown + --ignore-scripts = belt and suspenders) | Runtime supply-chain attacks (e.g., dynamic loading of bad code from a CDN) |

| Drive-by npm install of a brand-new transitive | Compromise of the registry itself (very rare; out of scope) |

Further reading

• Original Mini Shai-Hulud StepSecurity analysis (TanStack attack, 2026-05-11): <https://www.stepsecurity.io/blog/mini-shai-hulud-is-back-a-self-spreading-supply-chain-attack-hits-the-npm-ecosystem>
• npm min-release-age config: <https://docs.npmjs.com/cli/v11/using-npm/config>
• bun minimumReleaseAge config: <https://bun.com/docs/runtime/bunfig>
• OSV.dev API (free, unauth): <https://osv.dev/docs/#tag/api>
• Earlier Shai-Hulud worm context: <https://github.com/advisories?query=shai-hulud>