CVE-2020-12656 in Linux
Summary
by MITRE
gss_mech_free in net/sunrpc/auth_gss/gss_mech_switch.c in the rpcsec_gss_krb5 implementation in the Linux kernel through 5.6.10 lacks certain domain_release calls, leading to a memory leak. Note: This was disputed with the assertion that the issue does not grant any access not already available. It is a problem that on unloading a specific kernel module some memory is leaked, but loading kernel modules is a privileged operation. A user could also write a kernel module to consume any amount of memory they like and load that replicating the effect of this bug
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/04/2024
The vulnerability identified as CVE-2020-12656 represents a memory leak flaw within the Linux kernel's rpcsec_gss_krb5 implementation, specifically in the gss_mech_free function located in net/sunrpc/auth_gss/gss_mech_switch.c. This issue affects Linux kernel versions through 5.6.10 and stems from the absence of proper domain_release calls during the cleanup process of GSS mechanisms. The flaw occurs when kernel modules are unloaded, resulting in memory that should be freed remaining allocated within the system's memory space.
The technical nature of this vulnerability aligns with CWE-401, which categorizes memory leaks as a common software weakness where allocated memory is not properly deallocated. The gss_mech_free function fails to invoke the necessary domain_release operations that would normally occur during the cleanup of GSS (Generic Security Services) mechanism contexts. This oversight creates a scenario where memory allocated for GSS mechanism handling persists in the kernel's memory management system even after the relevant kernel modules have been unloaded, leading to gradual memory consumption over time.
From an operational perspective, the impact of this vulnerability manifests as a gradual degradation of system performance through memory exhaustion, particularly in environments where kernel modules are frequently loaded and unloaded. While the vulnerability does not introduce new access privileges or bypass existing security controls, it represents a resource consumption issue that could potentially be exploited for denial-of-service attacks. The memory leak occurs within the kernel's RPC security framework, specifically affecting the Kerberos 5 authentication mechanism used in network services. The vulnerability is particularly concerning in high-availability systems or environments where kernel module operations are frequent, as the accumulated memory leak could eventually lead to system instability or resource exhaustion.
The security implications of CVE-2020-12656 are mitigated by the fact that kernel module loading is a privileged operation, requiring root or equivalent administrative privileges. This means that unauthorized users cannot directly exploit this vulnerability to gain additional access rights. However, the vulnerability does represent a potential vector for resource exhaustion attacks, where an attacker with privileged access could repeatedly load and unload kernel modules to consume system memory. The disputed nature of this vulnerability reflects the industry's understanding that while the memory leak is a legitimate technical issue, it does not represent a significant security escalation. The ATT&CK framework would classify this as a resource exhaustion technique rather than a privilege escalation, focusing on the gradual consumption of system resources rather than unauthorized access. Organizations should implement proper monitoring for memory usage patterns and kernel module loading activities to detect potential exploitation attempts. The recommended mitigation involves updating to a patched kernel version where the domain_release calls have been properly implemented, ensuring that all allocated memory is correctly freed during module unloading operations.