CVE-2015-8569 in Linux
Summary
by MITRE
The (1) pptp_bind and (2) pptp_connect functions in drivers/net/ppp/pptp.c in the Linux kernel through 4.3.3 do not verify an address length, which allows local users to obtain sensitive information from kernel memory and bypass the KASLR protection mechanism via a crafted application.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-8569 resides within the Linux kernel's Point-to-Point Tunneling Protocol implementation, specifically affecting versions through 4.3.3. This issue manifests in two primary functions: pptp_bind and pptp_connect located in the drivers/net/ppp/pptp.c file. The flaw represents a critical security oversight that enables local attackers to exploit improper address length verification mechanisms, creating opportunities for information disclosure and bypass of kernel protection features. The vulnerability's impact extends beyond simple data leakage as it directly undermines the kernel's memory protection mechanisms, particularly KASLR (Kernel Address Space Layout Randomization) which serves as a fundamental defense against kernel exploitation techniques.
The technical exploitation of this vulnerability occurs through the manipulation of socket address parameters during PPTP protocol operations. When the pptp_bind and pptp_connect functions process network address information, they fail to validate the length of the provided socket address structures. This omission creates a potential for buffer over-read conditions where the kernel reads beyond allocated memory boundaries, inadvertently exposing kernel memory contents to user-space applications. The flaw operates at the kernel level and requires local system access, making it a local privilege escalation vector that can be leveraged by malicious processes already running on the system. The vulnerability's classification aligns with CWE-129, which addresses improper validation of length of input data, and specifically relates to improper input validation that allows for information disclosure through memory access violations.
The operational impact of CVE-2015-8569 extends significantly beyond simple information disclosure, as it enables attackers to bypass KASLR protection mechanisms that are essential for modern kernel security. By reading kernel memory contents, an attacker can potentially discover kernel base addresses, function pointers, and other sensitive information that would normally be randomized and protected. This information leakage fundamentally weakens the kernel's security posture and makes subsequent exploitation attempts more feasible. The vulnerability affects systems utilizing the PPTP protocol implementation and can be particularly dangerous in environments where kernel memory layout information could be used to craft more sophisticated attacks. The exploitation requires local access but provides a pathway for attackers to gain deeper insights into the kernel's operational state and memory layout.
Mitigation strategies for CVE-2015-8569 primarily focus on applying the official kernel patches released by the Linux kernel development team. System administrators should immediately upgrade to kernel versions that contain the necessary fixes, typically those released after the vulnerability disclosure. The patch addresses the core issue by implementing proper address length validation in both the pptp_bind and pptp_connect functions, ensuring that socket address parameters are properly verified before processing. Organizations should also consider implementing additional security controls such as restricting local user access to systems where PPTP functionality is enabled, as well as monitoring for suspicious network activity that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation in kernel space code and serves as a reminder of how seemingly minor implementation oversights can create significant security risks. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and information gathering, specifically targeting the kernel's memory management and address space protection mechanisms.