CVE-2021-3594 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 udp_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.
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Analysis
by VulDB Data Team • 10/25/2024
The vulnerability identified as CVE-2021-3594 represents a critical security flaw within the SLiRP networking implementation of QEMU virtualization software. This issue manifests as an invalid pointer initialization problem that specifically impacts the udp_input() function within the SLiRP library. The flaw is particularly concerning because it can be triggered when processing UDP packets that are smaller than the expected udphdr structure size, creating a scenario where memory access violations can occur. The vulnerability resides in the fundamental packet processing logic of the virtual network stack, making it a core component of the virtualization environment's security posture. This type of issue falls under the CWE-467 category of "Use of sizeof() on a Pointer Type" and represents a classic buffer over-read condition that can be exploited for information disclosure.
The technical execution of this vulnerability occurs when QEMU's SLiRP implementation processes malformed UDP packets that do not meet the expected header size requirements. When a UDP packet arrives that is smaller than the udphdr structure, the initialization of pointers within the udp_input() function fails to properly validate the packet boundaries, leading to potential out-of-bounds memory reads. This condition allows a malicious guest operating system to craft specially crafted UDP packets that can cause the host system to read memory locations that should remain protected. The memory disclosure occurs through indirect access patterns where the flawed pointer initialization leads to unauthorized data exposure from the host's memory space. This vulnerability specifically affects libslirp versions prior to 4.6.0, indicating that the issue was present in older versions and was subsequently addressed in the updated library.
The operational impact of CVE-2021-3594 extends beyond simple information disclosure to potentially compromise the confidentiality of sensitive data within the virtualized environment. When a guest operating system successfully exploits this vulnerability, it can gain access to host memory contents, potentially exposing confidential information such as cryptographic keys, passwords, or other sensitive data that resides in memory. The attack vector is particularly dangerous because it can be executed from within a compromised guest environment, making it a significant concern for multi-tenant cloud deployments where isolation between virtual machines is critical. The vulnerability can be leveraged as part of a broader attack chain to escalate privileges or extract additional sensitive information from the host system. This aligns with ATT&CK technique T1059.001 for command and control communications and T1566 for credential access through network-based attacks.
Mitigation strategies for this vulnerability should prioritize the immediate upgrade of libslirp to version 4.6.0 or later, which contains the necessary patches to address the pointer initialization flaw. System administrators should also implement network segmentation and monitoring to detect unusual UDP packet patterns that might indicate exploitation attempts. Additional protective measures include configuring QEMU virtual machines with restricted network access, implementing network-based intrusion detection systems, and conducting regular vulnerability assessments of virtualization environments. The remediation process should also include reviewing and updating virtualization security policies to ensure that guest operating systems cannot easily craft malicious packets that exploit memory access vulnerabilities. Organizations should consider implementing memory protection mechanisms such as stack canaries and address space layout randomization to further reduce the impact of potential exploitation attempts. Regular security updates and patch management procedures should be enforced across all virtualization infrastructure to prevent similar vulnerabilities from being exploited in the future.