CVE-2020-8557
Description
A flaw was found in Kubernetes, where the amount of disk space the /etc/hosts file can use is unconstrained . This flaw can allow attacker-controlled pods to cause a denial of service if they have permission to write to the node's /etc/hosts file.
Statement
In OpenShift Container Platform (OCP) there is LocalStorageCapacityIsolation feature gate functionality which prevents a denial of service (DoS) attack on the node by writing to the ephemeral storage.This feature is disabled by default in OCP 3.11 and can be enabled as per [1]. Even with enabled LocalStorageCapacityIsolation feature gate, OCP is affected by this vulnerability, therefore it is recommended to enable the feature gate and also upgrade to an OCP version which has a fix for this vulnerability.
[1] https://docs.openshift.com/container-platform/3.11/install_config/configuring_ephemeral.html
Mitigation
On OpenShift Container Platform (OCP) 3.11 and 4.x it's possible to set the allowPrivilegeEscalation Security Context Constraint to 'false' to prevent this. Note that this is set to 'true' by default, and setting it to false will prevent certain binaries which require setuid to stop working. On OCP 3.11 for example the 'ping' command will no longer work [1]. On OCP 4.x and later the 'ping' command will work with allowPrivilegeEscalation set to False, but other setuid binaries will not work.
[1] https://docs.openshift.com/container-platform/3.11/release_notes/ocp_3_11_release_notes.html
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.5 | 5.5 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
If an attacker can trigger the allocation of the limited resources, but the number or size of the resources is not controlled, then the most common result is denial of service. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment, i.e., the product may slow down, crash due to unhandled errors, or lock out legitimate users. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.
Access Control,Other
Technical Impact: Bypass Protection Mechanism; Other
In some cases it may be possible to force the product to "fail open" in the event of resource exhaustion. The state of the product -- and possibly the security functionality - may then be compromised.
Acknowledgements
Red Hat would like to thank the Kubernetes Product Security Committee for reporting this issue. Upstream acknowledges Kebe Liu (DaoCloud) as the original reporter.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
