CVE-2015-5327 in Linux
Summary
by MITRE
Out-of-bounds memory read in the x509_decode_time function in x509_cert_parser.c in Linux kernels 4.3-rc1 and after.
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Analysis
by VulDB Data Team • 12/30/2022
The vulnerability identified as CVE-2015-5327 represents a critical out-of-bounds memory read flaw within the Linux kernel's X.509 certificate parsing functionality. This issue specifically affects the x509_decode_time function located in the x509_cert_parser.c source file, which is responsible for processing time fields within X.509 certificates. The vulnerability manifests in kernel versions 4.3-rc1 and subsequent releases, making it a regression that impacts a significant portion of the Linux kernel ecosystem. The flaw occurs during the parsing of X.509 certificate time fields, where the kernel fails to properly validate the bounds of memory access operations, potentially allowing maliciously crafted certificates to trigger memory corruption.
This vulnerability falls under the CWE-129 weakness category, which specifically addresses improper validation of array indices and out-of-bounds memory access. The technical implementation of the flaw involves the x509_decode_time function not properly checking the length of time fields within certificate data structures before attempting to read from memory locations. When processing malformed X.509 certificates, particularly those with truncated or improperly formatted time fields, the kernel's certificate parser attempts to access memory beyond the allocated buffer boundaries. This results in a kernel memory read operation that extends beyond the intended data structure, potentially exposing sensitive kernel memory contents or causing system instability.
The operational impact of CVE-2015-5327 extends beyond simple memory corruption, as it provides potential attack vectors for privilege escalation and system compromise. Attackers can leverage this vulnerability by presenting specially crafted X.509 certificates to systems that process certificate validation, such as those handling TLS connections, code signing verification, or certificate-based authentication. The out-of-bounds read could expose kernel memory contents, potentially revealing sensitive information such as cryptographic keys, memory addresses, or other confidential data. Additionally, the memory corruption could lead to denial of service conditions or potentially enable more sophisticated exploitation techniques. This vulnerability is particularly concerning in environments where certificate validation is frequently performed, such as web servers, network infrastructure devices, and systems handling secure communications.
Mitigation strategies for CVE-2015-5327 primarily focus on immediate kernel updates and system hardening measures. Organizations should prioritize applying the official kernel patches released by Linux kernel maintainers, which typically involve adding proper bounds checking to the x509_decode_time function and ensuring that memory access operations validate buffer boundaries before execution. System administrators should also implement certificate validation policies that limit the acceptance of certificates from untrusted sources and monitor for unusual certificate processing activities. The ATT&CK framework categorizes this vulnerability under the T1059 technique for system command execution, as exploitation could potentially lead to privilege escalation. Additional defensive measures include implementing kernel memory protection mechanisms such as stack canaries, address space layout randomization, and kernel page table isolation to complicate exploitation attempts. Network segmentation and monitoring solutions should be configured to detect and alert on suspicious certificate validation activities that might indicate exploitation attempts.