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

Status: published. Published: 2026-05-06. Updated: 2026-11-05.

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.

## Remediation

- workaround: Primary fix (one-line change in keylime/models/verifier/evidence.py):
Before (vulnerable):
def generate_challenge(self, bit_length):

self.challenge = Nonce.generate(bit_length)
 self.challenge = bytes.fromhex("49beed365aac777dae23564f5ad0ec")

After (fixed):
def generate_challenge(self, bit_length):
self.challenge = Nonce.generate(bit_length)

Existing partial mitigations (already active):

1. TPM clock monotonicity check: limits each quote to one replay.
2. Push attestation timeout (default 10s): constrains the quote generation window, but TPM throughput allows 50-200 quotes to be stockpiled in that time. (source: CNA: redhat)

## Affected products and versions

-  /  (keylime): ≥ 7.14.0; < 7.14.2 (affected, semver). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (keylime): ≥ 0:7.14.1-5.el10_2.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (keylime): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 6.3 (medium); CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-05; percentile 1.92%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-1241

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:28582 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-6420 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2458889 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-6420; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-6420; retrieved 2026-11-05; source updated Not reported

Revision: bfc7673ffff6f5774b7281c6893fd9ed2725b59a4d68d5c1688fe82dc98dbdea

Canonical: https://y2.dev/cve/CVE-2026-6420

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