GHSA-wxrw-gvg8-fqjp Sliver has DNS C2 OTP Bypass that Allows Unauthenticated Session Flooding and Denial of Service

• Go github.com/bishopfox/sliver: < 1.6.12 → fixed in 1.6.12

Summary The DNS C2 listener accepts unauthenticated `TOTP` bootstrap messages and allocates server-side DNS sessions without validating OTP values, even when `EnforceOTP` is enabled. Because sessions are stored without a cleanup/expiry path in this flow, an unauthenticated remote actor can repeatedly create sessions and drive memory exhaustion. Vulnerable Component • `server/c2/dns.go:84-90` (`EnforceOTP` stored but not enforced in bootstrap) • `server/c2/dns.go:378-390` (`TOTP` requests routed directly to bootstrap) • `server/c2/dns.go:490-521` (`handleHello` allocates session without OTP validation) • `server/c2/dns.go:495` (`sessions.Store` with no lifecycle control in this path) • `client/command/jobs/dns.go:46-52` (operator-facing `EnforceOTP` control implies auth gate) • `implant/sliver/transports/dnsclient/dnsclient.go:896-900` (`otpMsg` sends `TOTP` with `ID=0`) • `protobuf/dnspb/dns.proto:22` (documents TOTP in `ID` field) Attack Vector • Network-accessible DNS listener • No authentication required • Low-complexity repeated DNS query loop • Trigger path: `DNSMessageType_TOTP` bootstrap handling Proof of Concept Preconditions • DNS listener is reachable • DNS C2 job is active Reproduction Steps 1. Send repeated DNS queries with a minimal protobuf message of type `TOTP`. 2. Observe repeated session allocation/issuance behavior. 3. Continue requests to increase active in-memory session state. Example ```bash while true; do dig +short @ baa8. A >/dev/null done ``` `baa8` is a base32 payload for a minimal TOTP-type protobuf message. Observable Indicators • Repeated bootstrap/session-allocation log entries from `handleHello` • Rising memory usage in the Sliver server process • Service slowdown or instability under sustained request volume Impact • Unauthenticated remote denial of service (availability) • Resource exhaustion through unbounded session growth in DNS bootstrap path • Estimated CVSS v3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` (7.5 High)