CVE-2026-49821

Fission: Cross-namespace Environment reference in Package allows build-time command execution and SA token exfiltration in github.com/fission/fission

### Summary Fission's `buildermgr` controller processed `Package` CRDs without verifying that `Package.spec.environment.namespace` matched `Package.metadata.namespace`. ### Details An attacker with `packages.fission.io/create` in their own namespace could set `spec.environment.namespace` to any other tenant's namespace. The controller then used its high-privilege service account to fetch the Environment cross-namespace and dispatch the build command into the **victim namespace's** builder pod. The build command's stdout is written verbatim into `Package.status.buildlog`. By running malicious code through an npm `preinstall` lifecycle hook (or any equivalent build step), the attacker could read the victim namespace's `fission-builder` Bearer token from inside that builder pod and surface it through the build log — then use the leaked token to read every Secret and ConfigMap in the victim namespace. ### Impact Cross-tenant compromise: a package author in one namespace could execute code inside another tenant's builder pod and exfiltrate that namespace's `fission-builder` service-account token, giving namespace-wide secret and configmap read in the victim namespace. ### Fix Fixed in [#3379](https://github.com/fission/fission/pull/3379) and released in [v1.24.0](https://github.com/fission/fission/releases/tag/v1.24.0). Two checks in series: - **Admission webhook** (`pkg/webhook/package.go::Validate`) rejects `Package.spec.environment.namespace != Package.metadata.namespace`. An empty namespace is still accepted; the controllers default it to the package's own namespace. - **Controller belt-and-braces:** the same check is repeated in `pkg/buildermgr/pkgwatcher.go::build` and `pkg/buildermgr/common.go::buildPackage` before the cross-namespace `Environments(...).Get` call, so a stale Package CR or a webhook-bypass cluster (`failurePolicy=Ignore`) cannot exploit the primitive either. ### Behavioural change Packages that explicitly set `spec.environment.namespace` to a different namespace are now rejected at admission. Empty-string remains accepted (resolves to the package's own namespace, the same as the prior implicit behaviour).