CVE-2023-30683: Improper Access Control in Telecom Prior to SMR Aug-2023 Release 1 Allows Local Attackers to Call endCall API Without Permission

In this long read, we will be exploring CVE-2023-30683, an improper access control vulnerability found in the Telecom software prior to the SMR Aug-2023 Release 1. The vulnerability allows local attackers to call the "endCall" API without proper permissions. We will discuss the exploit details, share related code snippets, and provide links to original references for further understanding of the vulnerability.

Exploit Details

The CVE-2023-30683 vulnerability, identified in the National Vulnerability Database (NVD) [1], has a Common Vulnerability Scoring System (CVSS) score of 7.8. This score indicates the vulnerability is of high severity, and may have serious consequences when exploited.

The nature of this vulnerability is an improper access control issue in the Telecom software. This issue allows a local attacker to call the "endCall" API without obtaining proper permissions. An attacker exploiting this vulnerability could potentially disconnect ongoing calls or misuse the API in various other ways.

The root cause of the vulnerability lies in the absence of a security mechanism to check the caller's permissions before allowing access to the "endCall" API. In other words, any local user of the application with knowledge of the API's availability can call it without restrictions.

Code Snippet

The following code snippet demonstrates the absence of permission checks in an example "endCall" API implementation in Telecom:

public class CallController {
	...
	public void endCall(Call call) {
		// No permission check is present here
		call.disconnect();
	}
}

As seen in the code snippet above, the "endCall" method accepts a "Call" object, but there is no mechanism in place that verifies the caller's permission before proceeding to disconnect the call. Thus, it is possible for an attacker to exploit this oversight by simply invoking the "endCall" method without proper authorization.

Possible Fix

To address the vulnerability, developers can implement a permission check within the "endCall" method to ensure that only authorized users can access it. The following code snippet shows a possible fix:

public class CallController {
	...
	// Include a method that checks for the required permission
	private void checkPermission(Context context) throws SecurityException {
		if (context.checkCallingOrSelfPermission("android.permission.END_CALL") != PackageManager.PERMISSION_GRANTED) {
			throw new SecurityException("Permission denied: endCall");
		}
	}
	
	// Modify the endCall method to include a call to checkPermission
	public void endCall(Call call, Context context) {
		checkPermission(context);  // Add permission check
		call.disconnect();
	}
}

In this updated code snippet, the "checkPermission" method verifies if the caller has the necessary "android.permission.END_CALL" permission. If not, the method throws a "SecurityException," effectively blocking unauthorized access to the "endCall" API.

Original References

- CVE-2023-30683 entry in the NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-30683
- CVSS score for CVE-2023-30683: https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?name=CVE-2023-30683&vector=AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H&version=3.1

Conclusion

CVE-2023-30683 is an improper access control vulnerability in Telecom allowing local attackers to call the "endCall" API without the required permissions. By implementing a proper permission check mechanism within the API, developers can mitigate the vulnerability and prevent unauthorized access to sensitive actions such as ending calls. As demonstrated in this post, understanding and addressing such vulnerabilities is crucial to ensure the security of software applications and their users.

Timeline

Published on: 08/10/2023 02:15:00 UTC
Last modified on: 08/14/2023 16:12:00 UTC