CVE-2023-4622 in Linux
Summary
by MITRE • 09/06/2023
A use-after-free vulnerability in the Linux kernel's af_unix component can be exploited to achieve local privilege escalation.
The unix_stream_sendpage() function tries to add data to the last skb in the peer's recv queue without locking the queue. Thus there is a race where unix_stream_sendpage() could access an skb locklessly that is being released by garbage collection, resulting in use-after-free.
We recommend upgrading past commit 790c2f9d15b594350ae9bca7b236f2b1859de02c.
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Analysis
by VulDB Data Team • 02/14/2025
The vulnerability identified as CVE-2023-4622 represents a critical use-after-free condition within the Linux kernel's af_unix networking implementation. This flaw exists in the unix_stream_sendpage() function which handles stream socket operations in the Unix domain socket family. The vulnerability stems from improper synchronization mechanisms during socket data transmission, creating a race condition that can be exploited by local attackers to escalate privileges. The issue specifically affects the handling of socket buffer management where data is appended to the peer's receive queue without adequate locking mechanisms.
The technical exploitation occurs through a race condition between the unix_stream_sendpage() function and the garbage collection process that releases socket buffer objects. When the sendpage function attempts to append data to the last socket buffer in a peer's receive queue, it accesses the socket buffer without proper locking, while garbage collection may simultaneously free that same buffer. This creates a window where the function references memory that has already been deallocated, resulting in a use-after-free condition that can be leveraged for arbitrary code execution. The vulnerability is classified as a CWE-416 Use After Free, which is a well-known class of memory safety issues that can lead to privilege escalation and system compromise.
From an operational perspective, this vulnerability poses significant risk to Linux systems as it enables local privilege escalation from user-level processes to kernel-level privileges. The exploitation requires local system access but does not need network connectivity or additional attack vectors, making it particularly dangerous in multi-user environments or systems where users might have limited access. Attackers can leverage this flaw to gain root privileges and potentially establish persistent backdoors or escalate their access to other system resources. The vulnerability affects all Linux kernel versions that include the problematic commit, making it widespread across numerous distributions and deployment scenarios.
The recommended mitigation strategy involves upgrading the kernel to a version that includes the fix for commit 790c2f9d15b594350ae9bca7b236f2b1859de02c, which implements proper locking mechanisms around socket buffer access operations. System administrators should prioritize patching affected systems and monitor for exploitation attempts through kernel logs and system monitoring tools. Additional mitigations include implementing strict user access controls, disabling unnecessary socket functionality, and maintaining comprehensive system logging to detect potential exploitation attempts. This vulnerability demonstrates the importance of proper synchronization in kernel-level code and aligns with ATT&CK technique T1068 for Local Privilege Escalation, specifically targeting kernel vulnerabilities for privilege elevation. Organizations should also consider implementing kernel hardening measures such as stack canaries and control flow integrity to further reduce the exploitability of similar memory corruption vulnerabilities.