# CVE-2026-6420: keylime Auth Bypass β€” Fixed in 7.14.2 🐍 🐍 PyPI Not in CISA KEV MEDIUM severity # CVE-2026-6420 β€” keylime MEDIUM CVE-2026-6420 is a medium-severity (CVSS 6.3) CWE-1241 vulnerability in keylime. A fix is available for keylime β€” see the affected versions and patch details below. Keylime: keylime: security bypass due to hardcoded tpm quote nonce Also known as[GHSA-q8w6-w55c-ccv5](/vulnerability/GHSA-q8w6-w55c-ccv5)PYSEC-2026-2548 Published May 6, 2026 Updated Nov 7, 2026 Affected 1 pkg Patched 1 / 1 Exploits None indexed Exploitation data as of Nov 10, 2026 Β· OSV.dev, NVD, FIRST.org (EPSS) ## Exploitation Status ### No confirmed exploitation observed yet - A successful exploit gives an attacker total control of the affected component, not partial access. - CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment. Exploitation and automatability from CISA’s SSVC triage for CVE-2026-6420. ## EPSS Exploitation Probability [via FIRST.org β†—](https://www.first.org/epss/) 0.1%probability of exploitation in next 30 days Lower Risk0.00% Lower risk than most CVEs2th percentile β€” riskier than 2% of all scored CVEsHighest risk 0.00%0.23%0.45%0.68%0.0%0.1%Jun 26Sep 26Nov 26 Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/). ## How urgent is this, really ## Where this sits among everything scored ## Real-World Exposure 1 pkg affected 🐍`keylime` Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages β€” download data is not available via public APIs for these ecosystems. ## Description ### 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 help gain access -- it only helps evade detection after root is obtained. No value against a machine the attacker already controls. UI None Fully automated after initial setup. S Unchanged AK signature binding confines impact to the single compromised agent. C High Compromised node continues receiving bootstrap keys, payloads, and secrets intended for trusted nodes. I High Verifier cannot distinguish a healthy system from a fully compromised one during the evasion window. A Low Only the compromised agent's revocation and incident response are suppressed; the system as a whole remains operational. The base score does not fully capture the operational severity: Keylime exists to detect machine compromise, so 8-33 minutes of undetected compromise is operationally critical. The fix is a one-line change and should be applied immediately regardless of the base score. #### Patches The fix restores the original random nonce generation (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) ``` Users should upgrade to the version containing this fix (7.14.2). #### Workarounds There is no complete workaround. The following existing mechanisms provide partial mitigation and are already active by default (no configuration needed): 1. **TPM clock monotonicity check** limits each distinct stockpiled quote to a single use, bounding the total evasion time. 2. **Push attestation timeout** (default 10s) prevents the attacker from going silent and constrains the quote generation window. Reducing `quote_interval` increases the attestation frequency but does not prevent the stockpiling attack. #### References - CWE-329: Generation of Predictable IV/Nonce (primary -- hardcoded nonce in cryptographic attestation protocol) - CWE-547: Use of Hard-Coded, Security-relevant Constants (hardcoded constant left in production code) - CWE-294: Authentication Bypass by Capture-replay (consequence -- enables replay attacks) - CWE-1241: Use of Predictable Algorithm in Random Number Generator - Introducing commit: [`2bf91197`](https://github.com/keylime/keylime/commit/2bf91197) via [PR #1814](https://github.com/keylime/keylime/pull/1814) - TCG TPM 2.0 Library Specification, Part 1, Section 18.4 (TPM2\_Quote) - IETF RATS Architecture (RFC 9334), Section 8 (Freshness) ## Affected Packages 1 total 1 fixed Ecosystem Package Vulnerable range Fix 🐍PyPI `keylime` β‰₯ 7.14.0&&< 7.14.2 7.14.2`pip install --upgrade 'keylime==7.14.2'` ## Detection & mitigation playbook Open-source dependency 1. ### Detect Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for keylime, including transitive dependencies β€” a direct dependency you never call can still pull in a vulnerable version. 2. ### Fix Update keylime to 7.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range β€” O3 confirms CVE-2026-6420 is resolved across your whole dependency graph. 3. ### Workarounds Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used. ## Fixing This On Your OS If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below β€” it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project. Red HatModerate Workaround published by Red Hat > 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: [Red Hat security advisory for CVE-2026-6420](https://access.redhat.com/security/cve/cve-2026-6420) (CC BY 4.0) Product Fixed in Advisory Red Hat Enterprise Linux 10 `keylime-0:7.14.1-5.el10_2.1` [RHSA-2026:28582](https://access.redhat.com/errata/RHSA-2026:28582) ## Frequently Asked Questions \## 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 attestatio O3 Security Β· Impact-Aware SCA ### Is CVE-2026-6420 in your dependencies? 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