CVE-2026-50570
Fission v1.24.0 added PodSpec safety validation for tenant-facing Environment and Function CRDs (ValidatePodSpecSafety / ValidateContainerSafety admission webhook + sanitizeContainerSecurityContext executor merge layer), but the
capability check was implemented as a fixed denylist of six Linux capabilities (SYS_ADMIN, NET_ADMIN, SYS_PTRACE, SYS_MODULE, DAC_READ_SEARCH, DAC_OVERRIDE). The denylist omitted **CAP_SYS_TIME**, among others. As a result, a tenant
who could create a Function or Environment CRD could request securityContext.capabilities.add: ["SYS_TIME"], pass Fission's admission validation and merge-layer sanitization, and run attacker-controlled code with CAP_SYS_TIME in the
resulting function or runtime container.
Demonstrated consequence: cross-tenant node integrity damage via CAP_SYS_TIME. The Linux real-time clock is not namespaced — time namespaces virtualize only MONOTONIC and BOOTTIME, never REALTIME — so a tenant container holding
CAP_SYS_TIME could call clock_settime(CLOCK_REALTIME) and rewrite the shared node wall clock. That corrupts TLS / certificate validity windows, Kubernetes lease renewal, token expiry, scheduling, and time-series for every workload on
the node.
The denylist also omitted SYS_RAWIO, BPF, SYS_RESOURCE, and MAC_ADMIN. Those are documented as evidence that the denylist is structurally incomplete (their practical impact is kernel-, LSM-, or device-cgroup-dependent and is not
exercised in this report).
The deeper structural problem: a denylist on capabilities.add cannot constrain capabilities the OCI runtime grants by default — DAC_OVERRIDE is in the OCI default cap set and reaches the container regardless of any add check,
partially mooting the denylist for its own entries. A capability allowlist (with drop:["ALL"] to remove the default set) is the only model that addresses both problems.
Affected
- Project: github.com/fission/fission
- Versions: <= 1.24.0
- Audited commits: v1.24.0 tag (ce617120) and current HEAD at audit
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Exploitation outlook
- Low exploitation risk0.27% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 20% of all EPSS-scored CVEs.
Advisory coverage (1)
External references
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