Directory Traversal Affecting github.com/cilium/cilium package, versions >=1.13.0 <1.13.1>=1.12.0 <1.12.8<1.11.15

github.com/cilium/cilium is an open source software for providing and transparently securing network connectivity and loadbalancing between application workloads such as application containers or processes.

Affected versions of this package are vulnerable to Directory Traversal. An attacker with access to a Cilium agent pod can write to /opt/cni/bin due to a hostPath mount of that directory in the agent pod. By replacing the CNI binary with their own malicious binary and waiting for the creation of a new pod on the node, the attacker can gain access to the underlying node.

Kubernetes RBAC should be used to deny users and service accounts exec access to Cilium agent pods.

In cases where a user requires exec access to Cilium agent pods, but should not have access to the underlying node, no workaround is possible.

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

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