How the CVE Works:
Libcontainer, a library used for container management, is vulnerable to a capabilities elevation issue when creating tenant containers. The tenant builder in libcontainer accepts a list of capabilities to be added to the tenant container’s specification. The logic in the code adds the provided capabilities to all capabilities of the main container if they are present in the spec. If not, it sets the provided capabilities as the tenant container’s capabilities. This behavior can lead to unintended elevation of privileges, as highlighted in GHSA-f3fp-gc8g-vw66. The issue arises because inherited capabilities are set without proper validation, allowing a tenant container to gain higher privileges than intended. Fixes in runc and crun address this by ensuring inherited capabilities are not set on tenant containers unless explicitly allowed.
DailyCVE Form:
Platform: Libcontainer
Version: Pre-fix versions
Vulnerability: Capabilities Elevation
Severity: Moderate
Date: Mar 21, 2025
What Undercode Say:
Exploitation:
- An attacker can exploit this vulnerability by crafting a tenant container with elevated capabilities, bypassing restrictions.
- By passing specific capabilities to the tenant builder, an attacker can inherit higher privileges from the main container.
- Exploitation requires direct use of libcontainer’s tenant builder with user-provided capabilities.
Protection:
- Avoid passing user-provided capabilities to the tenant builder.
- Validate and filter capabilities before setting them on tenant containers.
- Update to patched versions of libcontainer or use runc/crun, which address this issue.
Commands:
1. Check Capabilities:
`grep CapEff /proc/self/status`
This command shows the effective capabilities of the current process.
2. Filter Capabilities:
Use `capsh` to drop unnecessary capabilities:
`capsh –drop=CAP_SYS_ADMIN — -c “your_command”`
3. Verify Container Capabilities:
Inspect container capabilities using:
`docker inspect –format ‘{{.HostConfig.CapAdd}}’`
Code Snippets:
1. Capability Filtering in Go:
func filterCapabilities(caps []string) []string {
allowedCaps := []string{"CAP_NET_BIND_SERVICE", "CAP_CHOWN"}
var filteredCaps []string
for _, cap := range caps {
if contains(allowedCaps, cap) {
filteredCaps = append(filteredCaps, cap)
}
}
return filteredCaps
}
2. Prevent Capabilities Elevation:
Ensure tenant containers do not inherit capabilities:
func createTenantContainer(spec Spec) {
spec.Process.Capabilities = nil // Do not set inherited caps
}
3. Audit Capabilities in Containers:
Use `libcap` to audit capabilities:
capsh --print
Analytics:
- Impact: Moderate, as it requires specific conditions for exploitation.
- Affected Systems: Systems using libcontainer directly with tenant containers.
- Mitigation Rate: High, with proper filtering and updates.
By following these steps, you can mitigate the risks associated with this vulnerability and secure your container environments.
References:
Reported By: https://github.com/advisories/GHSA-5w4j-f78p-4wh9
Extra Source Hub:
Undercode
