iamprover 0.6.0

Formally verify security invariants over AWS IAM policies using an SMT solver (Z3), with counterexample traces.

iamprover

Formally verify security invariants over AWS IAM policies — with proofs, not pattern-matching.

Most IAM scanners grep for known misconfigurations. iamprover does something stronger: it encodes IAM policy-evaluation semantics into an SMT solver (Z3) and proves that your declared security invariants hold — or hands you a concrete counterexample (principal, action, resource) showing exactly how they break.

[FAIL] prod-data-read-restricted — Only the data-team role may read the prod-data bucket
    counterexample: arn:aws:iam::111122223333:role/ci-runner
        can perform  s3:getobject
        on resource  arn:aws:s3:::prod-data/A

[PASS] audit-logs-untouchable — No principal may perform any S3 action on the audit-logs bucket
[PASS] no-iam-mutation — No principal may mutate IAM (privilege-escalation surface)

2/3 invariants proven, 1 violated

The [PASS] lines are not "no findings" — they are proofs over all possible actions and resources, including every wildcard expansion.

Why

Individually-correct IAM policies compose into globally-unsafe states: a broad s3:Get* on one role quietly bypasses the least-privilege story your prod bucket policy tells. This tool grew out of research on exactly that failure mode — Security Invariants in Distributed Cloud Systems, which model-checks how per-service security enforcement breaks under cross-service composition. iamprover applies the same idea to real cloud policies: declare system-level invariants, verify them mechanically, get violation traces when they fail.

Install

pip install iamprover

Quickstart

1. Describe your principals and their policies (or point at a Terraform plan):

iamprover verify --account examples/account.json --invariants examples/invariants.yaml

2. Or gate a Terraform change in CI:

terraform show -json plan > plan.json
iamprover verify --tf-plan plan.json --invariants invariants.yaml   # exit 2 on violation

3. Or verify a live account — no Terraform required:

aws iam get-account-authorization-details > gaad.json
iamprover verify --gaad gaad.json --privesc --check-trust

4. Or use the GitHub Action to gate every pull request:

- uses: hashicorp/setup-terraform@v3
- run: terraform plan -out plan && terraform show -json plan > plan.json
- uses: UTKARSH698/iamprover@v0.4.0
  with:
    tf-plan: plan.json
    invariants: invariants.yaml
    privesc: "true"                # built-in privilege-escalation invariants
    privesc-unless: "arn:aws:iam::*:role/admin-*"

Invariants are declared in YAML:

invariants:
  - id: prod-data-read-restricted
    description: Only the data-team role may read objects in the prod-data bucket
    forbid:
      action: "s3:GetObject"
      resource: "arn:aws:s3:::prod-data/*"
    unless_principal:
      - "arn:aws:iam::111122223333:role/data-team"

  - id: no-passrole-lambda-escalation
    description: No single principal may both pass a role and create a Lambda
    forbid_chain:                  # fails only if ONE principal can do EVERY step
      - action: "iam:PassRole"
      - action: "lambda:CreateFunction"

Privilege-escalation invariants (v0.3)

--privesc enables a built-in catalog of the well-known AWS IAM escalation paths — policy-version rewrites, credential minting, policy attachment, trust-policy rewrites, code hijacking, and the iam:PassRole chains into Lambda, EC2, CloudFormation, Glue, and SageMaker:

iamprover verify --tf-plan plan.json --privesc \
    --privesc-unless "arn:aws:iam::111122223333:role/ops-admin"

Chains are verified compositionally: privesc-passrole-ec2 fails only if the solver finds a single principal allowed both iam:PassRole and ec2:RunInstances (each step checked as an independent request, so condition gates still count) — counterexamples list every step:

[FAIL] privesc-passrole-ec2 — Principal can launch an EC2 instance with a privileged instance profile ...
    counterexample: arn:aws:iam::111122223333:role/dev
        step 1: iam:passrole on *
        step 2: ec2:runinstances on *

Live accounts & cross-account trust (v0.4)

Point iamprover at a real account instead of a Terraform plan. --gaad ingests the output of aws iam get-account-authorization-details, flattening group memberships and managed-policy attachments and picking each policy's default version:

aws iam get-account-authorization-details > gaad.json
iamprover verify --gaad gaad.json --invariants invariants.yaml --privesc

--check-trust analyzes every role's trust policy for grants that reach outside its own account. External or public (Principal: "*") assume-role grants are flagged; a grant is "guarded" when scoped by sts:ExternalId, aws:PrincipalOrgID, aws:SourceAccount, or similar. Allowlist known partners with --trusted-account:

iamprover verify --gaad gaad.json --check-trust --trusted-account 444455556666

[TRUST-FAIL] arn:aws:iam::111122223333:role/partner-access
        assumable by arn:aws:iam::999988887777:root
        UNGUARDED — no ExternalId / org / source-account condition
[TRUST-INFO] arn:aws:iam::111122223333:role/vendor-scoped
        assumable by arn:aws:iam::444455556666:root
        guarded by   sts:ExternalId

Policy variables (${aws:username}, ${aws:PrincipalTag/team}, …) are widened to * in Action/Resource and treated as unknown in conditions — always in the over-approximating direction, so they never hide a violation. Tag-based condition keys are modeled as free request-context variables the solver searches over.

Bounding layers: permission boundaries, SCPs, RCPs (v0.5)

Identity- and resource-based policies only grant access; permission boundaries, Service Control Policies (SCPs), and Resource Control Policies (RCPs) only bound it — each must independently contain a matching Allow or that path is closed, and an explicit Deny in any of them blocks access outright. A permission boundary bounds identity-based access only; an RCP bounds resource-based access only; an SCP bounds both, account-wide:

iamprover verify --account account.json --invariants invariants.yaml \
    --scp org-scp.json --scp ou-scp.json --rcp account-rcp.json

--scp/--rcp are repeatable — pass one file per applicable layer (e.g. one per OU level) and each is treated as an independent cap, so the effective bound is their intersection while a deny in any one of them still applies. Permission boundaries attach per-principal: set permission_boundary on a principal in an --account file, or they're resolved automatically from PermissionsBoundaryArn when using --gaad. Absent any of these, evaluation is identical to v0.4.

Whole-system reachability: transitive AssumeRole chains (v0.6)

Every invariant above checks one principal's direct permissions. But a principal with no direct access can still reach it by assuming a role that has it: --closure assume-role widens every invariant to also cover principals reachable through sts:AssumeRole chains, not just direct grants:

iamprover verify --gaad gaad.json --invariants invariants.yaml --closure assume-role

An edge exists between two principals when the source's identity policy grants an assume-role action on the target and the target's trust policy allows the source — both sides are checked independently, matching how AWS actually evaluates sts:AssumeRole. Guarded trust conditions (ExternalId, org id, source account) don't block the edge: a guard is a value the assuming principal must supply, not a barrier to whether the relationship exists, so it stays on the over-approximating side. Counterexamples show the full chain:

[FAIL] no-s3-read
    counterexample: arn:aws:iam::111122223333:role/a
        step 1: sts:assumerole on arn:aws:iam::111122223333:role/b
        step 2: s3:getobject on arn:aws:s3:::prod-data/x

Chain length is bounded by --max-hops (default 4) — AWS environments rarely need deep AssumeRole chains, so a bounded search gives predictable runtime on large live-account graphs while still catching realistic escalation paths. --closure is deliberately a mode, not a boolean, so future closure relations (e.g. iam:PassRole into service execution) can be added as new values without another flag.

What is modeled (v0.6)

• Allow/Deny with explicit-deny-overrides-allow and default deny
• Action / NotAction / Resource / NotResource with * and ? wildcards
• Case-insensitive action matching (as IAM does it)
• Condition blocks: StringEquals/Like (and Not/Arn variants), Bool, IpAddress/NotIpAddress (IPv4 CIDR, exact via bitvector encoding). The solver searches over all request contexts and counterexamples include the context (with context aws:multifactorauthpresent = true, …); invariants can pin context with a where: clause
• Resource-based policies (e.g. bucket policies) with Principal: "*" or exact ARNs, unioned with identity-based grants; --check-anonymous verifies invariants for an unauthenticated principal (catches public grants)
• Terraform plans: inline policies, managed policies via attachments (resolved by ARN or configuration reference), and aws_s3_bucket_policy
• Invariant exemptions by exact ARN or glob
• Multi-step forbid_chain invariants (one principal holding every step) and a built-in privilege-escalation catalog (--privesc)
• Live-account ingestion (--gaad) with group/managed-policy flattening; cross-account trust analysis (--check-trust); policy variables and tag-based condition keys
• Permission boundaries (identity-path bound), SCPs (identity- and resource-path bound), and RCPs (resource-path bound), each as an independent, intersecting cap (--scp/--rcp, repeatable)
• Whole-system reachability (--closure assume-role): invariants extend over principals reachable through bounded sts:AssumeRole chains, not just direct grants, with the chain shown in the counterexample

Soundness note: unsupported condition operators degrade safely — treated as always-true on Allow and always-false on Deny — so permissions are only ever over-approximated: iamprover may flag violations a condition would prevent (false positives), but within the modeled fragment it will not miss one (no false negatives). Trust the PASSes; investigate the FAILs.

Roadmap

• v0.3 — GitHub Action on the Marketplace · privilege-escalation chain detection (iam:PassRole → lambda:CreateFunction, iam:CreateAccessKey, …) as built-in invariants ✅ shipped
• v0.4 — live-account ingestion via aws iam get-account-authorization-details · cross-account trust analysis · policy variables and tag-based conditions ✅ shipped
• v0.5 — permission boundaries, SCPs, and RCPs as intersecting bounding layers ✅ shipped
• v0.6 — access-analyzer-style reachability across the full principal graph (transitive sts:AssumeRole chains) ✅ shipped
• v0.7+ — richer closure relations beyond sts:AssumeRole (e.g. iam:PassRole into service execution), moving from a principal-to-principal graph toward a full identity/capability/resource attack graph

Development

pip install -e ".[dev]"
pytest

License

Apache-2.0