CVE-2026-6420 — Keylime: keylime: security bypass due to hardcoded tpm quote nonce

Affected: keylime, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9

A flaw was found in Keylime. An attacker with root access on an enrolled monitored machine, where the Keylime agent runs, can exploit a vulnerability in the Keylime verifier. The verifier uses a hardcoded challenge nonce for Trusted Platform Module (TPM) quote attestation instead of a cryptographically random value. This allows the attacker to stockpile valid TPM quotes and replay them to evade detection after compromising the system. This issue affects only the push model deployment.

GHSA-q8w6-w55c-ccv5 — Keylime has a hardcoded attestation challenge nonce that allows replay attacks

Affected: PyPI: keylime

## CVE-2026-6420: Hardcoded attestation challenge nonce allows replay attacks

### Impact

The `CertificationParameters.generate_challenge()` method in the push attestation protocol uses a hardcoded challenge nonce instead of generating a cryptographically random value. This removes the nonce-based replay protection from TPM quote attestation.

An attacker with root access on a monitored agent node can exploit this by stockpiling valid TPM quotes (using `tpm2_quote` with the known nonce) before compromising the system, then replaying them to evade detection by the verifier. The push attestation timeout (~10s) constrains the generation window, but TPM throughput allows stockpiling ~50-200 quotes, enabling approximately 8-33 minutes of undetected compromise with default settings.

The attack is limited to a single agent node (AK signature binding prevents cross-agent replay). The pull-mode (legacy) attestation path is not affected.

**Affected versions:** >= 7.14.0, <= 7.14.1

**CVSS:** 6.3 Medium (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L`)

| Metric | Value | Rationale | |---|---|---| | AV | Local | Exploitation requires local access to the agent machine (stop agent, access TPM, run replacement). The network transmission of quotes to the verifier is normal protocol operation. | | AC | Low | Deterministic attack: publicly visible nonce, standard `tpm2-tools`, no race conditions. | | PR | High | Root on a legitimate enrolled node is required. The vulnerability does not hel…

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CVE-2026-6420 — Keylime: keylime: security bypass due to hardcoded tpm quote nonce

GHSA-q8w6-w55c-ccv5 — Keylime has a hardcoded attestation challenge nonce that allows replay attacks