Netflix Lemur up to 1.9.2 ACME Client /api/1/authorities setup_acme_client_no_retry acme_url certificate validation

Summaryinfo

A vulnerability identified as problematic has been detected in Netflix Lemur up to 1.9.2. This impacts the function setup_acme_client_no_retry of the file /api/1/authorities of the component ACME Client. This manipulation of the argument acme_url causes certificate validation. The identification of this vulnerability is CVE-2026-70666. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Netflix Lemur up to 1.9.2. It has been declared as problematic. Affected by this vulnerability is the function setup_acme_client_no_retry of the file /api/1/authorities of the component ACME Client. The manipulation of the argument acme_url with an unknown input leads to a certificate validation vulnerability. The CWE definition for the vulnerability is CWE-295. The product does not validate, or incorrectly validates, a certificate. As an impact it is known to affect integrity. The summary by CVE is:

Lemur manages TLS certificate creation. Prior to 1.9.3, an authority-role member could update acme_url through PUT /api/1/authorities/ without revalidation and direct setup_acme_client_no_retry to an attacker-controlled ACME server. ACME directory and order responses contain newNonce, newOrder, authorizations, and finalize URLs chosen by that server. The Lemur ClientV2 followed those URLs without requiring their host to match the configured directory host, allowing JWS-signed requests to internal services or cloud metadata endpoints. The issue required an ACME authority and a user authorized for that authority, but did not require global administrator privileges. The fix revalidates updates and introduces _PinnedClientNetwork to enforce a single allowed host for the complete ACME flow. This issue is fixed in version 1.9.3.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-70666 since 08/04/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1587.003 according to MITRE ATT&CK.

Upgrading to version 1.9.3 eliminates this vulnerability.

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Productinfo

Vendor

• Netflix

Name

• Lemur

Version

• 1.9.0
• 1.9.1
• 1.9.2

Website

• Product: https://github.com/Netflix/lemur/

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