CVE-2023-3773 in Linux
Summary
by MITRE • 07/25/2023
A flaw was found in the Linux kernel’s IP framework for transforming packets (XFRM subsystem). This issue may allow a malicious user with CAP_NET_ADMIN privileges to cause a 4 byte out-of-bounds read of XFRMA_MTIMER_THRESH when parsing netlink attributes, leading to potential leakage of sensitive heap data to userspace.
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Analysis
by VulDB Data Team • 11/12/2025
The vulnerability identified as CVE-2023-3773 resides within the Linux kernel's IP framework, specifically within the XFRM subsystem responsible for packet transformation operations. This subsystem handles the processing of network packets through various security mechanisms including encryption, authentication, and tunneling operations. The flaw manifests as a boundary condition error in the netlink attribute parsing logic that governs how the kernel processes configuration requests from userspace applications. The vulnerability is particularly concerning because it operates within the core networking infrastructure that manages secure communications between networked systems.
The technical implementation of this vulnerability stems from improper validation of the XFRMA_MTIMER_THRESH attribute during netlink message processing. When a malicious user with CAP_NET_ADMIN capabilities submits a crafted netlink message containing this specific attribute, the kernel's parsing routine fails to properly bounds-check the data structure access. This results in a 4-byte out-of-bounds read operation that accesses memory locations beyond the intended buffer boundaries. The XFRMA_MTIMER_THRESH attribute controls timer thresholds for the transformation subsystem, but the parsing code does not adequately validate the attribute's length or content before performing memory accesses. This type of flaw falls under CWE-129 Input Validation and CWE-787 Out-of-bounds Read, representing a classic buffer overread vulnerability that can expose sensitive kernel memory contents.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides an attacker with access to potentially sensitive heap data that may contain kernel memory structures, cryptographic keys, or other confidential information. The requirement for CAP_NET_ADMIN privileges limits the attack surface to users who already possess significant network administration capabilities, but this privilege escalation path remains concerning for systems where such capabilities are granted to untrusted users or where privilege boundaries are not properly enforced. The 4-byte read operation may expose small but potentially valuable fragments of kernel memory that could be used in subsequent attacks or for information gathering purposes. According to ATT&CK framework, this vulnerability aligns with T1068 Privilege Escalation and T1552 Credential Access, as it could potentially lead to the extraction of sensitive data from kernel memory spaces.
Mitigation strategies for CVE-2023-3773 should focus on both immediate patching and operational security improvements. The primary solution involves applying the kernel patches released by the Linux kernel security team that correct the bounds-checking logic in the XFRM subsystem's netlink attribute parsing code. Organizations should prioritize updating their kernel versions to patched releases, particularly in environments where CAP_NET_ADMIN capabilities are granted to users who cannot be fully trusted. Additionally, implementing proper privilege separation and limiting the scope of CAP_NET_ADMIN capabilities can reduce the attack surface. Network administrators should also consider monitoring for suspicious netlink attribute usage patterns and implementing runtime protections that can detect anomalous memory access patterns. The vulnerability demonstrates the importance of rigorous input validation in kernel subsystems and highlights the need for comprehensive security testing of core networking components.