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shankar0123
b813660c74
Problem (CWE-306 Missing Authentication for Critical Function):
internal/service/scep.go PKCSReq skipped the shared-secret check when
s.challengePassword was empty. An unconfigured-but-enabled SCEP server
accepted any unauthenticated client reaching /scep and issued a
certificate against the configured issuer for any CSR with a valid
signature. No audit trail distinguished authenticated from
unauthenticated enrollments. This matches the two-layer fail-closed
pattern already used for C-2 (f549a7a): reject at startup AND reject
at the service boundary.
Fix (two layers, defense-in-depth):
Layer 1 — startup pre-flight in cmd/server/main.go:
preflightSCEPChallengePassword returns a non-nil error when SCEP is
enabled and CERTCTL_SCEP_CHALLENGE_PASSWORD is empty. main logs and
os.Exit(1)s before the SCEP service is constructed. Disabled SCEP is
unaffected. The helper is unit-testable in isolation.
Layer 2 — service-layer rejection in internal/service/scep.go:
PKCSReq refuses enrollment when s.challengePassword == "" even though
main already blocks this state — protects future call sites (tests,
library reuse, a REST-over-HTTPS wrapper). When a secret is
configured, the comparison now uses crypto/subtle.ConstantTimeCompare
so response time does not leak the configured secret through a
short-circuiting byte compare.
Files:
- cmd/server/main.go: preflightSCEPChallengePassword helper; call site
inside the `if cfg.SCEP.Enabled` block before issuer lookup; fatal
slog error references CWE-306 and names the env var so operators can
diagnose the startup failure without reading code.
- cmd/server/main_test.go: TestPreflightSCEPChallengePassword with five
table-driven subtests (disabled empty, disabled set, enabled empty
rejected, enabled set, single-char boundary). The enabled-empty case
asserts the error string contains both CERTCTL_SCEP_CHALLENGE_PASSWORD
and CWE-306 so the log message remains actionable.
- internal/config/config.go: SCEPConfig.ChallengePassword godoc now
states the field is REQUIRED when SCEP.Enabled and cross-references
preflightSCEPChallengePassword.
- internal/service/scep.go: imports crypto/subtle; PKCSReq rewritten
with the two-layer check; comment block cites H-2 / CWE-306 and the
constant-time rationale.
- internal/service/scep_test.go: existing tests that relied on the
vulnerable empty-password path now configure a secret on both sides.
TestSCEPService_PKCSReq_ChallengePassword_NotRequired is replaced by
TestSCEPService_PKCSReq_ChallengePassword_EmptyServerConfigRejected
which iterates ["", "any-value", "guess"] against an unconfigured
server and asserts "not configured" in the error. A new
TestSCEPService_PKCSReq_ChallengePassword_ConstantTimeLengthIndependence
exercises same-prefix-longer and wrong-case inputs to guard against a
regression from ConstantTimeCompare to a short-circuiting byte compare.
- internal/service/m11c_crypto_enforcement_test.go: four tests
(RejectsWeakKey, AcceptsStrongKey, MaxTTL_ForwardedToIssuer,
NoProfileRepo_PassesThrough) constructed NewSCEPService with an empty
challenge password and exercised PKCSReq through the now-rejected
vulnerable path. All four now configure "secret123" on both sides with
an inline H-2 comment; the crypto/MaxTTL/profile behavior they assert
is unchanged.
Wire-format / behavioral invariants preserved:
- RFC 8894 SCEP handler is untouched (internal/api/handler/scep.go and
internal/pkcs7/*): GetCACaps/GetCACert responses, PKIOperation request
parsing, and the PKCS#7 certs-only response format are byte-identical.
- RFC 7030 EST handler is untouched
(internal/api/handler/est.go + internal/pkcs7/*).
- Revocation idempotency composite key (H-1, migration 000012) untouched.
- AES-256-GCM config encryption (C-2) untouched.
- CRL DER bytes and OCSP response bytes unchanged.
Verification:
- go build ./... silent success
- go vet ./... silent success
- go test -race -count=1 ./internal/service/ ./cmd/server/
./internal/api/handler/ ./internal/integration/ all OK
- Coverage with comfortable headroom over CI gates:
service 67.8% (gate 55%)
handler 79.0% (gate 60%)
domain 92.7% (gate 40%)
middleware 80.0% (gate 30%)
cmd/server 1.6% (preflightSCEPChallengePassword: 100%)
internal/service/scep.go PKCSReq statement coverage: 100%.
- rg sweeps: no `s.challengePassword != ""` remains;
no `challengePassword != s.challengePassword` remains.
Operational note: operators with SCEP enabled but no challenge password
set will see a fatal startup error and a log line citing
CERTCTL_SCEP_CHALLENGE_PASSWORD and CWE-306 after upgrading. This is the
intended fail-closed behavior. Fix by either setting the env var to a
non-empty shared secret or setting CERTCTL_SCEP_ENABLED=false.
Audit report: certctl-audit-report.md (revision 5) logs this under
H-2 Resolution Log.