CVE-2023-42669: Samba's "rpcecho" Development Server Vulnerability and Exploitation

A security vulnerability has recently been discovered in the "rpcecho" development server within Samba, a non-Windows RPC server used to test different elements of Samba's DCE/RPC stack. This vulnerability, identified as CVE-2023-42669, could potentially lead to service disruptions and a complete denial-of-service (DoS) attack on the Active Directory Domain Controller (AD DC).

The Vulnerability

The CVE-2023-42669 security vulnerability stems from an issue in the "dcesrv_echo_TestSleep()" function, which can be blocked indefinitely under specific conditions due to a "sleep()" call. The problem arises from the fact that the "rpcecho" service only has one worker in the main RPC task, causing calls to the "rpcecho" server to be blocked for a given duration when exploited.

Original references

- Samba's official advisory: https://www.samba.org/samba/security/CVE-2023-42669.html
- Repository with affected code: https://github.com/samba-team/samba

Here is a sample of the affected code in the "dcesrv_echo_TestSleep()" function

static void dcesrv_echo_TestSleep(struct dcesrv_call_state *dce_call,
				   TALLOC_CTX *mem_ctx,
				   struct echo_TestSleep *r)
{
	sleep(r->in.seconds);
	r->out.seconds = r->in.seconds;
}

As we can see, the function makes a "sleep()" call and waits for a specific time based on the value of "r->in.seconds".

The Exploit

Both authenticated users and attackers can exploit this vulnerability by making calls to the "rpcecho" server, requesting it to block for a specific time and effectively deadlock most services. This leads to a complete denial of service on the AD DC and has a significant impact on all other services since "rpcecho" runs in the main RPC task.

Mitigation and Resolution

To mitigate and protect against this vulnerability, users and administrators are advised to update their Samba installations to a patched version. Samba has released security updates to address this vulnerability and prevent malicious actors from exploiting it. You can find the updated versions here: https://www.samba.org/samba/download/

Additionally, it is also recommended to restrict access to the "rpcecho" server only to trusted and authorized users, further reducing the risk of exploitation.

Conclusion

In conclusion, the CVE-2023-42669 vulnerability found in Samba's "rpcecho" development server can potentially lead to service disruptions and denial of service attacks. Users and administrators are strongly advised to update their Samba installations and implement necessary security measures to protect their systems and networks from exploitation. Be proactive in keeping your environment and software up-to-date to mitigate the risk against emerging threats like this vulnerability.

Timeline

Published on: 11/06/2023 07:15:09 UTC
Last modified on: 11/24/2023 09:15:08 UTC