CVE-2020-25643 in Linux
Summary
by MITRE • 10/06/2020
A flaw was found in the HDLC_PPP module of the Linux kernel in versions before 5.9-rc7. Memory corruption and a read overflow is caused by improper input validation in the ppp_cp_parse_cr function which can cause the system to crash or cause a denial of service. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
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Analysis
by VulDB Data Team • 11/16/2020
The vulnerability identified as CVE-2020-25643 resides within the HDLC_PPP module of the Linux kernel, representing a critical memory corruption flaw that affects systems running kernel versions prior to 5.9-rc7. This issue manifests through improper input validation within the ppp_cp_parse_cr function, which serves as a crucial component in the Point-to-Point Protocol implementation. The flaw operates at the kernel level, making it particularly dangerous as it can be exploited to compromise system stability and security. The vulnerability falls under the category of memory safety issues and is classified as a read overflow condition that can lead to unpredictable system behavior.
The technical exploitation of this vulnerability occurs when the ppp_cp_parse_cr function fails to properly validate input data during PPP control protocol parsing operations. This improper validation allows maliciously crafted input packets to trigger memory corruption through a read overflow condition, where the function attempts to read beyond allocated memory boundaries. The flaw demonstrates characteristics consistent with CWE-125, which describes out-of-bounds read vulnerabilities, and CWE-787, which covers out-of-bounds write conditions that can result in memory corruption. Attackers can leverage this weakness by sending specially crafted PPP control packets that exploit the input validation gap, potentially causing kernel memory corruption that leads to system crashes or denial of service conditions.
The operational impact of CVE-2020-25643 extends beyond simple system availability concerns to encompass data confidentiality and integrity threats. When exploited, the vulnerability can cause system crashes that result in complete denial of service for network connectivity services relying on PPP protocols. The memory corruption aspect presents risks to data integrity as corrupted memory regions may contain sensitive information or system state data. Network infrastructure devices such as routers, firewalls, and network access servers that utilize PPP connections are particularly vulnerable, as these systems often serve as critical points of network access and control. The vulnerability can be especially problematic in environments where continuous network availability is essential, as the denial of service impact can disrupt critical network services and potentially provide attackers with opportunities for further exploitation.
Mitigation strategies for CVE-2020-25643 primarily focus on kernel version upgrades to 5.9-rc7 or later releases where the vulnerability has been addressed through proper input validation implementation. System administrators should prioritize patching affected systems, particularly those running older kernel versions that support PPP functionality. Network monitoring should be enhanced to detect anomalous PPP traffic patterns that might indicate exploitation attempts. Additionally, implementing network segmentation and access controls can limit the potential impact of exploitation attempts. The vulnerability's classification under ATT&CK technique T1071.004 for application layer protocol manipulation highlights the need for network traffic inspection capabilities. Organizations should also consider implementing intrusion detection systems that can identify suspicious PPP control packet structures and monitor for potential exploitation attempts, as the flaw represents a significant threat to network infrastructure availability and security.