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GHSA-pmqp-h87c-mr78 CVE-2019-11253 GO-2022-0703

XML Entity Expansion and Improper Input Validation in Kubernetes API server

High Go
Severity
7.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
25.94%
Chance of exploitation in the next 30 days. Higher than 97.98% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-20 Improper Input Validation
CWE-776 Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
Fix
1.13.12
Upgrade k8s.io/kubernetes to this version or later

Description

Improper input validation in the Kubernetes API server in versions v1.0-1.12 and versions prior to v1.13.12, v1.14.8, v1.15.5, and v1.16.2 allows authorized users to send malicious YAML or JSON payloads, causing the API server to consume excessive CPU or memory, potentially crashing and becoming unavailable. Prior to v1.14.0, default RBAC policy authorized anonymous users to submit requests that could trigger this vulnerability. Clusters upgraded from a version prior to v1.14.0 keep the more permissive policy by default for backwards compatibility.

Specific Go Packages Affected

k8s.io/kubernetes/pkg/apiserver

Affected versions

Go

PackageVulnerableFixed in
k8s.io/kubernetes
>= 1.0.0, < 1.13.12
1.13.12
k8s.io/kubernetes
>= 1.14.0, < 1.14.8
1.14.8
k8s.io/kubernetes
>= 1.15.0, < 1.15.5
1.15.5
k8s.io/kubernetes
>= 1.16.0, < 1.16.2
1.16.2
k8s.io/kubernetes
>= 1.0.0, < 1.13.12
>= 1.14.0, < 1.14.8
>= 1.15.0, < 1.15.5
>= 1.16.0, < 1.16.2
1.13.12
1.14.8
1.15.5
1.16.2

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

k8s.io/kubernetes Go → 1.13.12

go
go get k8s.io/kubernetes@v1.13.12 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Weakness

CWE-20: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How to prevent it
  • Architecture and Design: Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
  • Architecture and Design: Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
  • Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
  • Implementation: Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
  • Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
  • Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
  • Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

CWE-776: Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

The product uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities.

How to prevent it
  • Operation: If possible, prohibit the use of DTDs or use an XML parser that limits the expansion of recursive DTD entities.
  • Implementation: Before parsing XML files with associated DTDs, scan for recursive entity declarations and do not continue parsing potentially explosive content.

References

Advisories

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
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GHSA-4x4m-3c2p-qppc
Kubernetes Nodes can delete themselves by adding an OwnerReference
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GHSA-hj2p-8wj8-pfq4
kubernetes allows nodes to bypass dynamic resource allocation authorization checks
Low Also affects k8s.io/kubernetes
GO-2025-3547
Kubernetes kube-apiserver Vulnerable to Race Condition
Low Also affects k8s.io/kubernetes
GHSA-3wgm-2gw2-vh5m
Kubernetes GitRepo Volume Inadvertent Local Repository Access
Medium Also affects k8s.io/kubernetes
GHSA-vv39-3w5q-974q
Kubernetes allows Command Injection affecting Windows nodes via nodes/*/logs/query API
Medium Also affects k8s.io/kubernetes
GHSA-jgfp-53c3-624w
Node Denial of Service via kubelet Checkpoint API
Medium Also affects k8s.io/kubernetes
GHSA-27wf-5967-98gx
Kubernetes kubelet arbitrary command execution
High Also affects k8s.io/kubernetes
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