CVE-2021-3592 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 bootp_input() function and could occur while processing a udp packet that is smaller than the size of the 'bootp_t' structure. A malicious guest could use this flaw to leak 10 bytes of uninitialized heap memory from the host. 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-2021-3592 represents a critical memory safety issue within the SLiRP networking implementation used by QEMU virtualization software. This flaw manifests in the bootp_input() function where improper handling of UDP packets leads to invalid pointer initialization. The vulnerability specifically occurs when processing UDP packets that are smaller than the expected bootp_t structure size, creating a condition where uninitialized heap memory becomes accessible to malicious actors. The technical nature of this issue places it firmly within CWE-457: Use of Uninitialized Variable, which directly relates to improper initialization of memory regions that can lead to information disclosure and potential exploitation. The vulnerability affects libslirp versions prior to 4.6.0, indicating that this was a recognized issue that required specific patching to resolve the memory handling inconsistency.
The operational impact of this vulnerability extends beyond simple information leakage, as it enables a malicious guest operating system to extract 10 bytes of uninitialized heap memory from the host system. This memory leakage could potentially contain sensitive information such as cryptographic keys, session tokens, or other confidential data that was previously stored in the uninitialized memory regions. The attack vector requires a compromised guest operating system with network access, making it particularly dangerous in multi-tenant virtualization environments where guest isolation is paramount. From an ATT&CK framework perspective, this vulnerability maps to T1059.001: Command and Scripting Interpreter - PowerShell and T1566.001: Phishing - Spearphishing Attachment, as it could enable attackers to establish persistent access through information gathering and privilege escalation techniques. The confidentiality threat level is particularly severe because heap memory often contains sensitive data structures, making this a prime target for attackers seeking to compromise system integrity.
The mitigation strategy for CVE-2021-3592 involves immediate upgrading of libslirp to version 4.6.0 or later, which contains the necessary patches to properly initialize memory pointers and validate packet sizes before processing. System administrators should also implement network segmentation and monitoring to detect anomalous packet behavior that might indicate exploitation attempts. Virtualization environments should enforce strict guest operating system isolation and consider implementing additional memory protection mechanisms such as heap randomization and stack canaries. The vulnerability highlights the importance of proper memory management in network stack implementations and serves as a reminder that seemingly minor initialization flaws can have significant security implications. Organizations using QEMU or related virtualization platforms should conduct thorough security assessments to identify other potential memory corruption issues and implement comprehensive monitoring to detect any exploitation attempts. This vulnerability underscores the critical need for rigorous input validation and proper memory initialization practices in network protocol implementations, particularly in virtualization environments where the attack surface is expanded by the presence of multiple guest operating systems sharing the same host resources.