CVE-2026-34984: External Secrets Operator has DNS exfiltration via getHostByName in its v2 template engine
Summary
The v2 template engine in runtime/template/v2/template.go imports Sprig’s TxtFuncMap() and removes env and expandenv, but leaves getHostByName available to user-controlled templates. Because ESO executes templates inside the controller process, an attacker who can create or update templated ExternalSecret resources can trigger controller-side DNS lookups using secret-derived values, creating a DNS exfiltration primitive.
Impact This is a confidentiality issue. In environments where untrusted or lower-trust users can author templated ExternalSecret resources and the controller can perform DNS resolution, fetched secret material can be exfiltrated through DNS without requiring direct outbound access from the attacker’s workload.
Other sources
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.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-34984?
CVE-2026-34984 has been classified as a critical vulnerability due to its potential for DNS exfiltration.
How can I mitigate CVE-2026-34984?
To mitigate CVE-2026-34984, you should update to External Secrets Operator version 2.3.0 or later immediately.
What are the affected versions for CVE-2026-34984?
CVE-2026-34984 affects External Secrets Operator versions from 2.0.0 to 2.2.0.
What is the impact of CVE-2026-34984?
The impact of CVE-2026-34984 allows an attacker to exfiltrate sensitive information via user-controlled templates through the getHostByName function.
Is there a fixed version available for CVE-2026-34984?
Yes, the fixed version for CVE-2026-34984 is External Secrets Operator version 2.3.0.