CVE-2019-17055 in Linux
Summary
by MITRE
base_sock_create in drivers/isdn/mISDN/socket.c in the AF_ISDN network module in the Linux kernel through 5.3.2 does not enforce CAP_NET_RAW, which means that unprivileged users can create a raw socket, aka CID-b91ee4aa2a21.
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Analysis
by VulDB Data Team • 12/29/2023
The vulnerability identified as CVE-2019-17055 resides within the Linux kernel's mISDN (multi-channel ISDN) subsystem, specifically in the base_sock_create function located in drivers/isdn/mISDN/socket.c. This flaw affects kernel versions through 5.3.2 and represents a significant privilege escalation risk that undermines the kernel's security model. The mISDN subsystem provides support for ISDN (Integrated Services Digital Network) protocols and operates within the AF_ISDN address family namespace, making it accessible to applications requiring ISDN communication capabilities. The vulnerability stems from the absence of proper capability checks during socket creation, specifically the failure to enforce CAP_NET_RAW capability requirements that should normally restrict access to raw socket creation.
The technical implementation of this vulnerability involves the mISDN network module's socket creation process failing to validate whether the requesting process possesses the necessary privileges to create raw sockets. In standard Linux security practices, raw socket creation requires the CAP_NET_RAW capability, which is typically restricted to privileged processes or those with elevated permissions. However, the base_sock_create function in the AF_ISDN module bypasses this validation, allowing any unprivileged user to create raw sockets through the mISDN subsystem. This represents a direct violation of the principle of least privilege and undermines the kernel's mandatory access controls that normally prevent unprivileged processes from accessing low-level network primitives. The flaw essentially creates a backdoor pathway through which non-privileged users can bypass kernel security boundaries and gain access to raw network socket functionality that should otherwise be restricted.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to leverage the mISDN subsystem for various malicious activities. An unprivileged user could potentially construct and send raw ISDN frames, perform network reconnaissance, or even craft sophisticated attacks that exploit the underlying ISDN protocol stack. The vulnerability is particularly concerning in environments where ISDN interfaces are present, as it allows for persistent access to network communication capabilities that could be used for data exfiltration, network monitoring, or as a foothold for further system compromise. This flaw can be exploited in both local and remote attack scenarios, depending on the system configuration and available attack vectors, making it a significant concern for system administrators and security professionals managing Linux-based systems with ISDN capabilities.
Mitigation strategies for CVE-2019-17055 should focus on immediate kernel updates to versions that address the capability validation issue, as well as operational security measures to limit exposure. System administrators should ensure that all Linux systems running kernel versions through 5.3.2 are updated to patched versions that properly enforce CAP_NET_RAW requirements for raw socket creation within the AF_ISDN module. Additionally, organizations should implement monitoring for unauthorized socket creation activities and consider disabling the mISDN subsystem entirely if ISDN interfaces are not actively required. The vulnerability aligns with CWE-276, which addresses improper privileges, and can be categorized under ATT&CK technique T1068, which involves exploiting privileges for privilege escalation. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of such vulnerabilities and ensure comprehensive defense-in-depth strategies are in place to protect against similar privilege escalation attacks.