CVE-2015-4037 in QEMU
Summary
by MITRE
The slirp_smb function in net/slirp.c in QEMU 2.3.0 and earlier creates temporary files with predictable names, which allows local users to cause a denial of service (instantiation failure) by creating /tmp/qemu-smb.*-* files before the program.
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Analysis
by VulDB Data Team • 05/20/2022
The vulnerability described in CVE-2015-4037 resides within the QEMU virtualization software version 2.3.0 and earlier, specifically within the slirp_smb function located in the net/slirp.c file. This flaw represents a classic predictable temporary file creation issue that can be exploited to disrupt system operations. The vulnerability manifests when QEMU creates temporary files using predictable naming conventions, specifically those following the pattern /tmp/qemu-smb.- which can be easily anticipated by local attackers. The issue stems from insufficient randomness in the temporary file generation process, allowing malicious users to preemptively create files with identical names before QEMU attempts to create them, thereby causing instantiation failures and subsequent denial of service conditions. This vulnerability falls under the category of predictable temporary file generation as classified by CWE-377, which is a well-documented weakness in software security practices.
The technical implementation of this vulnerability involves the slirp_smb function's approach to creating temporary files for SMB (Server Message Block) protocol handling within the QEMU network stack. When QEMU initializes SMB functionality, it generates temporary files in the /tmp directory using deterministic naming patterns that do not incorporate sufficient entropy or randomization. Attackers can exploit this predictability by creating their own temporary files with the same naming convention before QEMU attempts to create its own files. This race condition scenario results in QEMU's file creation operations failing, leading to instantiation failures that ultimately cause the virtualization environment to become unresponsive or crash. The vulnerability is particularly concerning because it requires no elevated privileges to exploit, as it only requires local access to create temporary files in the /tmp directory.
The operational impact of CVE-2015-4037 extends beyond simple denial of service to potentially compromise the entire virtualization environment. When QEMU fails to create necessary temporary files for SMB functionality, it can cause the guest operating system to lose network connectivity or experience complete system instability. This vulnerability is especially dangerous in production environments where QEMU instances may be running critical applications or services that depend on network connectivity. The attack vector is straightforward and effective, as local users can simply create the required files in the /tmp directory to trigger the denial of service condition. The vulnerability affects QEMU versions up to and including 2.3.0, representing a significant security gap in virtualization software that could be exploited by any local user with access to the system.
Mitigation strategies for CVE-2015-4037 should focus on addressing the root cause of predictable temporary file creation within the QEMU codebase. The primary solution involves implementing proper randomization in temporary file naming conventions to ensure that generated filenames cannot be easily predicted by attackers. This approach aligns with the principle of least privilege and secure coding practices recommended by various security frameworks including the OWASP Secure Coding Practices. System administrators should upgrade to QEMU versions that have patched this vulnerability, specifically versions beyond 2.3.0 where the temporary file creation logic has been improved to use proper randomization. Additionally, implementing proper file system permissions and access controls for the /tmp directory can help mitigate potential exploitation, though this represents a secondary defense mechanism. The vulnerability also highlights the importance of proper input validation and secure temporary file handling practices as outlined in the MITRE ATT&CK framework under the technique of privilege escalation through file system manipulation. Organizations should also consider implementing monitoring and alerting mechanisms to detect unusual patterns of temporary file creation that might indicate exploitation attempts.