CVE-2021-3593 in QEMU
Summary
by MITRE • 06/16/2021
An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw exists in the udp6_input() function and could occur while processing a udp packet that is smaller than the size of the 'udphdr' structure. This issue may lead to out-of-bounds read access or indirect host memory disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw affects libslirp versions prior to 4.6.0.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 10/25/2024
The vulnerability identified as CVE-2021-3593 represents a critical security flaw within the SLiRP networking implementation used by QEMU virtualization software. This issue manifests as an invalid pointer initialization problem that specifically affects the udp6_input() function within the libslirp library. The vulnerability arises when processing UDP packets that are smaller than the expected udphdr structure size, creating a scenario where memory access patterns become unpredictable and potentially exploitable. The flaw demonstrates characteristics consistent with CWE-467, which describes the use of sizeof() on a pointer type rather than the object pointed to, leading to incorrect memory calculations and potential memory access violations.
The technical execution of this vulnerability occurs during network packet processing within the virtualized environment where guest operating systems communicate with the host system through SLiRP networking. When a malformed UDP packet is received that is smaller than the udphdr structure, the improper pointer initialization causes the system to read beyond the allocated memory boundaries. This results in out-of-bounds read access that can potentially expose sensitive host memory contents to the guest operating system, creating a significant confidentiality risk. The vulnerability specifically impacts versions of libslirp prior to 4.6.0, indicating that this was a known issue that required a specific version update to address the underlying memory management flaw.
From an operational perspective, this vulnerability poses a severe threat to data confidentiality within virtualized environments, as it allows guest operating systems to potentially access and disclose sensitive information from the host system's memory space. The attack vector typically involves sending specially crafted UDP packets to the virtual machine's network interface, which then triggers the vulnerable code path in the SLiRP implementation. This type of vulnerability aligns with ATT&CK technique T1059.001, which involves the use of command and scripting interpreters, though in this case the attack is more subtle and involves memory access rather than direct command execution. The impact extends beyond simple information disclosure, as the leaked memory could contain sensitive data such as encryption keys, passwords, or other confidential information that could be leveraged for further attacks.
The mitigation strategy for CVE-2021-3593 requires immediate updating of libslirp to version 4.6.0 or later, which contains the necessary patches to address the invalid pointer initialization issue. System administrators should prioritize patching QEMU installations that utilize SLiRP networking, particularly in environments where guest operating systems have network access to the host. Additional defensive measures include implementing network segmentation and access controls to limit the potential attack surface, monitoring for unusual network traffic patterns that might indicate exploitation attempts, and ensuring that virtualization environments are properly isolated. Organizations should also consider implementing network intrusion detection systems that can identify and alert on malformed UDP packets that might be attempting to exploit this vulnerability, as the issue represents a potential pathway for privilege escalation and data exfiltration attacks within virtualized computing environments.