CVE-2026-59341
MediumCVSS 4.2Exploitation Probability (EPSS)
Low risk24th percentile - higher than 24% of all known CVEs
Summary
A vulnerability exists in the Sealed Secrets controller's unauthenticated POST endpoints /v1/verify and /v1/rotate. An attacker with internal network access can inject custom Go template logic into spec.template.data and use differential HTTP response codes (200 vs 409) as a decryption oracle to recover the full plaintext of any sealed secret. The issue is exacerbated by missing AEAD label binding for spec.template.data, allowing arbitrary modification of that field while keeping the ciphertext valid.
Risk Assessment
Any pod within the Kubernetes cluster or anyone with kubectl port-forward access can unauthenticatedly decrypt arbitrary sealed secrets, leading to exposure of passwords, API keys, and other sensitive data. This can result in full compromise of protected systems and privilege escalation within the cluster.
Recommendation
Update the Sealed Secrets controller to a version containing the fix as soon as possible (refer to the project's official advisory). Until patched, restrict network access to the controller's :8080 port to trusted components only and consider rotating all sealed secrets that may have been exposed.
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Original NVD description (English source)
A security vulnerability exists in the Sealed Secrets controller's unauthenticated POST endpoints. By submitting a modified payload containing custom Go template logic in spec.template.data, an attacker with internal network access can abuse the handler as a decryption oracle to recover the full plaintext of any sealed secret. The POST /v1/verify and /v1/rotate handlers call Unseal() to decrypt target secrets, then render any Go templates found in spec.template.data.* using the decrypted payload as the evaluation context (pkg/apis/sealedsecrets/v1alpha1/sealedsecret_expansion.go). Errors encountered during template execution are directly reflected in the resulting HTTP response status codes. Missing AEAD label binding: the spec.template.data field is omitted from the AEAD authenticated-data label binding ciphertext to metadata. As a result, an attacker can copy a target's valid metadata and encryptedData verbatim, satisfying AEAD decryption and label validation, while freely replacing spec.template.data with arbitrary template logic. Side-channel oracle: template execution errors map directly to HTTP response codes. HTTP 200 (OK) indicates template execution succeeded; HTTP 409 (Conflict) indicates template execution failed (e.g. via {{ fail "..." }}). By injecting conditional statements such as {{ if eq (substr 0 1 .password) "S" }}ok{{ else }}{{ fail "x" }}{{ end }}, an attacker receives an HTTP 200 status when a character guess is correct and an HTTP 409 when it is incorrect. This differential response leaks one character-equality bit per request, allowing full secret extraction over successive queries. Attack vector & prerequisites: unauthenticated; requires network access to the controller's internal service port (:8080). Although this service is not exposed to the public internet by default, it is accessible to any pod within the Kubernetes cluster or via a kubectl port-forward connection.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS