A flaw was found in the USB redirector device (usb-redir) of QEMU. Small USB packets are combined into a single, large transfer request, to reduce the overhead and improve performance. The combined size of the bulk transfer is used to dynamically allocate a variable length array (VLA) on the stack without proper validation. Since the total size is not bounded, a malicious guest could use this flaw to influence the array length and cause the QEMU process to perform an excessive allocation on the stack, resulting in a denial of service.
The CVSS score for CVE-2021-3527 is 5.5, indicating a medium severity level. This vulnerability poses a significant risk to organizations using affected versions of QEMU, as it could lead to service interruptions.
Organizations should prioritize patching immediately. The vulnerability affects QEMU versions up to 6.0.0, and remediation is essential to avoid potential denial of service conditions.
As of now, there are no known exploits or public proofs of concept available for this vulnerability. However, the potential for exploitation remains a concern, particularly in environments where untrusted guests can interact with the USB redirector.
Vulnerability Details
CVE-2021-3527 affects the USB redirector device in QEMU, which concatenates small USB packets into larger transfer requests. This method, while intended to improve performance, leads to the creation of variable-length arrays on the stack without adequate size validation. The flaw is classified under CWE-770, indicating an issue with improper handling of input data.
The vulnerability was published on May 26, 2021, and is officially classified as medium severity, with a CVSS v3.1 score of 5.5. The attack vector is local, requiring low complexity and low privileges, with no user interaction necessary.
Technical Analysis
The root cause of the vulnerability lies in the processing of USB transfer requests in the QEMU USB redirector. When small USB packets are combined for efficiency, the resultant size is used to allocate memory on the stack. Without checks to limit the size of this allocation, a guest could manipulate the process to request an excessive amount of memory, leading to a denial of service through stack exhaustion.
The attack vector is local, meaning that an attacker would need access to the QEMU environment. The attack complexity is low, as it does not require advanced skills or detailed knowledge of the system. Furthermore, the attacker requires low privileges, as the vulnerability does not necessitate special access rights to exploit.
Risk & Impact Analysis
Risk to organizations includes the potential for denial of service, which could disrupt operations and lead to downtime. Given that the availability impact is classified as high, organizations must assess their exposure to this vulnerability, especially if they are operating untrusted guest environments.
The urgency assessment for this vulnerability is classified as medium. While there is no immediate threat of exploitation, organizations should not delay in applying patches as a preventive measure.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
CVE-2021-3527 affects the following versions: QEMU versions prior to 6.0.0, Red Hat Enterprise Linux 8.0, and Debian Linux 9.0 and 10.0.
Mitigation & Remediation
To mitigate this vulnerability, organizations should apply patches as they become available. The specific patches for QEMU can typically be found in the official repositories. If immediate patching is not possible, organizations should consider implementing network controls to restrict access to untrusted guests.
Penetration testing can also help identify further vulnerabilities in the environment.
Detection Guidance
Organizations should monitor logs for unusual memory allocation patterns and errors related to stack overflows. Additionally, behavioral anomalies in guest interactions with USB devices should be noted.
AppSecure Threat Intelligence Insight
CVE-2021-3527 highlights the importance of validating input sizes in stack allocations to prevent denial of service vulnerabilities. This incident serves as a reminder for security teams to review their configurations and ensure that untrusted inputs are correctly handled.
Understanding penetration testing methodology can provide valuable insights into securing systems against such vulnerabilities.
Designing an effective vulnerability management program will also help organizations to proactively identify and remediate weaknesses.
Cloud penetration testing strategies can further enhance security posture against potential exploits.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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