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securitycritical PriorityID: sigstore-slsa-v1-provenance-gate

Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate

Enforces mandatory SLSA v1.0 in-toto provenance verification using Sigstore Fulcio certificate identities and Rekor transparency log proofs before admitting container workloads into production environments. Rejects images deployed by mutable tag, lacking cryptographically verified subject digests, or missing non-forgeable CI/CD OIDC claims.

Prohibited Anti-Pattern: Deploying Mutable Container Tags with Unverified Build Provenance and Unvalidated OIDC Signer Identities

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---
description: Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate - Enforces mandatory SLSA v1.0 in-toto provenance verification using Sigstore Fulcio certificate identities and Rekor transparency log proofs before admitting container workloads into production environments. Rejects images deployed by mutable tag, lacking cryptographically verified subject digests, or missing non-forgeable CI/CD OIDC claims.
globs: .github/workflows/**/*.{yml,yaml}, policies/**/*.{yaml,rego}, k8s/**/*.{yml,yaml}, src/admission/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/sigstore-slsa-v1-provenance-gate"
---

# Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: Deploying Mutable Container Tags with Unverified Build Provenance and Unvalidated OIDC Signer Identities

## System Constraints
You are a Principal Security Architect enforcing the Sigstore SLSA v1.0 Provenance Attestation Policy Gate. You mandate cryptographic verification of container image digests against Rekor transparency logs and Fulcio OIDC certificates. You strictly forbid deploying mutable image tags, ignoring SLSA v1.0 predicate validations, or relying on non-enforced admission pathways.

## Strict Guidelines
- Engineers MUST ALWAYS reference container images by immutable cryptographic digests (image@sha256:...) and NEVER by mutable tags alone.
- Engineers MUST verify the in-toto attestation envelope using Sigstore bundle verification, confirming Rekor inclusion proof and Fulcio root-of-trust.
- Services MUST validate that the Fulcio certificate SAN extension matches the expected OIDC repository identity and trusted workflow ref (e.g., https://github.com/org/repo/.github/workflows/release.yml@refs/heads/main).
- Services MUST inspect the predicateType 'https://slsa.dev/provenance/v1' and ensure the external parameters match the immutable source commit digest.
- Components NEVER admit workloads if signature verification fails, transparency log entry is missing, or bundle verification encounters a network/timeout failure (fail-closed).

## Bad vs Good Implementations
### Sigstore Admission Webhook: Attestation and OIDC Identity Enforcement

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The webhook checks for ':latest' as a naive string operation, permits other mutable tags, and performs zero cryptographic verification of the container signature, Sigstore bundle, Rekor log proof, or SLSA v1.0 provenance.
```typescript
import { Request, Response } from 'express';

interface AdmissionRequestBody {
  request?: {
    object?: {
      spec?: {
        containers?: Array<{ name: string; image: string }>;
      };
    };
  };
}

export async function admissionWebhookHandler(req: Request, res: Response): Promise<void> {
  const body = req.body as AdmissionRequestBody;
  const containers = body.request?.object?.spec?.containers || [];

  for (const container of containers) {
    // ANTI-PATTERN: Accepts mutable tags and checks only string patterns without cryptographic verification
    if (container.image.endsWith(':latest')) {
      res.status(400).json({ allowed: false, status: { message: 'Cannot use latest tag' } });
      return;
    }
    // ANTI-PATTERN: Blindly trusts image without checking Rekor log or Fulcio identity
  }

  res.json({ allowed: true });
}
```

#### Production Standard (Correct)
> **Standard**: Enforces immutable SHA256 digest pinning, cryptographically verifies the Sigstore bundle against Rekor and Fulcio OIDC claims, validates the SLSA v1.0 predicate type, and confirms the attested subject matches the container digest.
```typescript
import { Request, Response } from 'express';
import { verify } from '@sigstore/verify';

interface ContainerSpec {
  name: string;
  image: string;
}

const TRUSTED_ISSUER = 'https://token.actions.githubusercontent.com';
const TRUSTED_SAN = 'https://github.com/my-org/core-service/.github/workflows/build.yml@refs/heads/main';
const SLSA_V1_PREDICATE = 'https://slsa.dev/provenance/v1';

export async function admissionWebhookHandler(req: Request, res: Response): Promise<void> {
  const containers: ContainerSpec[] = req.body?.request?.object?.spec?.containers ?? [];

  for (const container of containers) {
    const digestMatch = container.image.match(/^.+@sha256:([a-f0-9]{64})$/);
    if (!digestMatch) {
      res.status(400).json({
        allowed: false,
        status: { message: `Image ${container.image} must be pinned to an immutable sha256 digest` }
      });
      return;
    }

    const imageDigest = digestMatch[1];
    const bundle = req.body?.attestationBundle;

    if (!bundle) {
      res.status(403).json({
        allowed: false,
        status: { message: `Missing Sigstore attestation bundle for ${container.image}` }
      });
      return;
    }

    try {
      const result = await verify(bundle, {
        keylessOptions: {
          identityProvider: TRUSTED_ISSUER,
          san: TRUSTED_SAN
        },
        rekorOptions: { verifyTlogEntry: true }
      });

      const payload = JSON.parse(Buffer.from(result.payload, 'base64').toString('utf8'));
      const subject = payload.subject?.find((s: { digest?: { sha256?: string } }) => s.digest?.sha256 === imageDigest);

      if (!subject || payload.predicateType !== SLSA_V1_PREDICATE) {
        res.status(403).json({
          allowed: false,
          status: { message: `SLSA v1.0 provenance predicate validation failed for ${container.image}` }
        });
        return;
      }
    } catch (err: unknown) {
      res.status(403).json({
        allowed: false,
        status: { message: `Cryptographic Sigstore verification failed: ${(err as Error).message}` }
      });
      return;
    }
  }

  res.json({ allowed: true });
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

GitHub Model Context Server
Query CI/CD workflow runs, OIDC token claims, and repository release immutability settings directly from coding agents.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Cosign CLI
Sigstore command-line tool for signing, verifying, and checking container attestations in Rekor.
SLSA Verifier
Official verification tool for SLSA build provenance artifacts and container images.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate

Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate defines an industrial-grade behavioral standard for security engineering. Enforces mandatory SLSA v1.0 in-toto provenance verification using Sigstore Fulcio certificate identities and Rekor transparency log proofs before admitting container workloads into production environments. Rejects images deployed by mutable tag, lacking cryptographically verified subject digests, or missing non-forgeable CI/CD OIDC claims. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Deploying Mutable Container Tags with Unverified Build Provenance and Unvalidated OIDC Signer Identities Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftDeploying Mutable Container Tags with Unverified Build Provenance and Unvalidated OIDC Signer IdentitiesCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS reference container images by immutable cryptographic digests (image@sha256

Engineers MUST ALWAYS reference container images by immutable cryptographic digests (image@sha256:...) and NEVER by mutable tags alone.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST verify the in-toto attestation envelope using Sigstore bundle verification, confirming Rekor inclusion proof and Fulcio root-of-trust.

Engineers MUST verify the in-toto attestation envelope using Sigstore bundle verification, confirming Rekor inclusion proof and Fulcio root-of-trust.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST validate that the Fulcio certificate SAN extension matches the expected OIDC repository identity and trusted workflow ref (e.g., https

Services MUST validate that the Fulcio certificate SAN extension matches the expected OIDC repository identity and trusted workflow ref (e.g., https://github.com/org/repo/.github/workflows/release.yml@refs/heads/main).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Services MUST inspect the predicateType 'https

Services MUST inspect the predicateType 'https://slsa.dev/provenance/v1' and ensure the external parameters match the immutable source commit digest.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Components NEVER admit workloads if signature verification fails, transparency log entry is missing, or bundle verification encounters a network/timeout failure (fail-closed).

Components NEVER admit workloads if signature verification fails, transparency log entry is missing, or bundle verification encounters a network/timeout failure (fail-closed).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Cryptographic Sigstore SLSA v1.0 Provenance and Immutability Gate critical for AI coding assistants?

Enforces mandatory SLSA v1.0 in-toto provenance verification using Sigstore Fulcio certificate identities and Rekor transparency log proofs before admitting container workloads into production environments. Rejects images deployed by mutable tag, lacking cryptographically verified subject digests, or missing non-forgeable CI/CD OIDC claims. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Deploying Mutable Container Tags with Unverified Build Provenance and Unvalidated OIDC Signer Identities) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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