Recently, a use-after-free vulnerability (CVE-2023-1195) has been discovered in the Linux kernel. This flaw is present in the reconn_set_ipaddr_from_hostname function in the fs/cifs/connect.c file. Researchers discovered that the Linux kernel fails to set the server hostname's free pointer to NULL, causing an invalid pointer request, which could potentially be exploited by attackers to cause denial-of-service or even execute arbitrary code on the affected system.

The problematic code snippet can be found in the fs/cifs/connect.c file

static int
reconn_set_ipaddr_from_hostname(struct TCP_Server_Info *server)
{
...
    memset(server->hostname, , server->hostname_len);
    memcpy(server->hostname, server->vals->domain_name,
        server->hostname_len);
    rc = addr.sockaddr.sockaddr_storage.ss_family == AF_UNSPEC;
    if (rc)
        rc = -EINVAL;
out:
    kfree(server->hostname);
    return rc;
}


In the above code snippet, the issue occurs when the kfree(server->hostname) is called without setting the server->hostname pointer to NULL after freeing it.

Original References

The vulnerability has been reported in the Linux kernel mailing list and can be found here. According to the original report by researcher Tobias Stöckmann, this flaw dates back to Linux kernel version 5.8..

The security patch addressing this vulnerability can be found in the kernel commit under the reference PATCH 2/3 cifs: make sure to NULL server->hostname after a failed reconnect. The fix, proposed by Aurelien Aptel, sets server->hostname pointer to NULL after freeing the allocated memory.

Exploit Details

A potential attacker could exploit this use-after-free vulnerability by injecting malicious code that manipulates the memory that was freed but not set to NULL, causing the kernel to access an invalid memory location. This could lead to denial-of-service (DoS) attacks and, in some cases, even allow the attacker to execute arbitrary code on the targeted system.

Mitigation

To mitigate this vulnerability, users are advised to apply the latest kernel patches for their Linux distribution. The patch in question is available in the Linux kernel repository and is expected to be included in future distribution updates. Users should also monitor the mailing lists and support channels for their specific distribution for further information on applying the patch.

Additionally, system administrators should ensure to always apply security updates promptly and follow best practices related to maintaining a secure environment, such as network segmentation, access control, and monitoring.

In conclusion, the CVE-2023-1195 vulnerability is a use-after-free flaw that stems from an oversight in the Linux kernel's hostname handling code. Affected users should apply the appropriate patches and follow standard security protocols to maintain system integrity.

Timeline

Published on: 05/18/2023 22:15:00 UTC
Last modified on: 05/26/2023 18:27:00 UTC