CVE-2023-54085 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix NULL pointer dereference on fastopen early fallback
In case of early fallback to TCP, subflow_syn_recv_sock() deletes the subflow context before returning the newly allocated sock to the caller.
The fastopen path does not cope with the above unconditionally dereferencing the subflow context.
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Analysis
by VulDB Data Team • 01/02/2026
The vulnerability CVE-2023-54085 represents a critical NULL pointer dereference issue within the Linux kernel's Multipath TCP implementation. This flaw specifically affects the MPTCP (Multipath TCP) subsystem which enables TCP connections to utilize multiple paths simultaneously for improved performance and reliability. The vulnerability manifests when the MPTCP implementation experiences an early fallback to standard TCP functionality, a scenario that occurs when certain conditions prevent the multipath connection from operating as intended.
The technical root cause of this vulnerability lies in the improper handling of subflow contexts during the fast open connection process. When an early fallback to TCP occurs, the function subflow_syn_recv_sock() executes a sequence of operations that includes deleting the subflow context before returning the newly allocated socket to the calling function. This deletion operation creates a situation where subsequent code paths attempting to access the subflow context through the fast open mechanism encounter a NULL pointer reference. The fast open path in MPTCP does not implement proper checks to handle this unconditional dereferencing of a potentially null subflow context, leading to a kernel panic or system crash.
The operational impact of this vulnerability extends beyond simple system instability, as it represents a potential denial of service condition that could be exploited by remote attackers. When triggered, the NULL pointer dereference causes the kernel to terminate abruptly, resulting in system crashes that can affect network connectivity and overall system availability. This vulnerability is particularly concerning in environments where MPTCP is actively used for high-performance networking, as it could be leveraged to disrupt critical network services or applications that depend on multipath connectivity. The vulnerability affects the kernel's network stack integrity and could potentially provide attackers with opportunities to gain unauthorized access to system resources or cause sustained service disruptions.
Mitigation strategies for CVE-2023-54085 should focus on applying the official kernel patches released by the Linux kernel development team, which address the specific NULL pointer dereference issue in the MPTCP fast open implementation. System administrators should prioritize updating their kernel versions to include the fix, particularly in production environments where MPTCP functionality is actively utilized. Additionally, monitoring network traffic patterns for unusual behavior that might indicate exploitation attempts can serve as an early warning system. The vulnerability aligns with CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. From an ATT&CK framework perspective, this vulnerability could be categorized under T1499.004 for network denial of service and potentially T1566.001 for initial access through network-based attacks that leverage kernel-level vulnerabilities. Organizations should also consider implementing network segmentation and access controls to limit potential exploitation vectors while applying the necessary kernel updates to fully remediate the vulnerability.