CVE-2026-34984: External Secrets Operator has DNS exfiltration via getHostByName in its v2 template engine

Vulnerability summary

CVE-2026-34984 is a high (CVSS 7.1) vulnerability in external-secrets external_secrets_operator. EPSS estimates a 0.45% chance of exploitation in the next 30 days, higher than 37.9% of scored vulnerabilities.

Timeline

1. 14-04-2026
   PublishedVulnerability first disclosed.
2. 14-04-2026
   Last modifiedVulnerability information updated.

Description

External Secrets Operator reads information from a third-party service and automatically injects the values as Kubernetes Secrets. Versions 2.2.0 and below contain a vulnerability in runtime/template/v2/template.go where the v2 template engine removes env and expandenv from Sprig's TxtFuncMap() but leaves the getHostByName function accessible to user-controlled templates. Since ESO executes templates within the controller process, an attacker who can create or update templated ExternalSecret resources can invoke controller-side DNS lookups using secret-derived values. This creates a DNS exfiltration primitive, allowing fetched secret material to be leaked via DNS queries without requiring direct outbound network access from the attacker's workload. The impact is a confidentiality issue, particularly in environments where untrusted or lower-trust users can author templated ExternalSecret resources and the controller has DNS resolution capability. This issue has been fixed in version 2.3.0.

• CWE-200Exposure of Sensitive Information to an Unauthorized ActorThe product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.