CVE-2017-7482 in Linux
Summary
by MITRE
In the Linux kernel before version 4.12, Kerberos 5 tickets decoded when using the RXRPC keys incorrectly assumes the size of a field. This could lead to the size-remaining variable wrapping and the data pointer going over the end of the buffer. This could possibly lead to memory corruption and possible privilege escalation.
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Analysis
by VulDB Data Team • 12/09/2022
The vulnerability described in CVE-2017-7482 represents a critical buffer overflow condition within the Linux kernel's handling of Kerberos 5 tickets through the RXRPC key management system. This flaw exists in kernel versions prior to 4.12 and specifically affects how the system processes authentication tickets during remote procedure calls. The issue manifests when the kernel attempts to decode Kerberos 5 tickets, where an incorrect assumption about field sizes leads to improper buffer boundary calculations. This misassessment occurs in the cryptographic key handling subsystem that manages remote authentication operations, creating a scenario where memory corruption can occur during legitimate authentication processes.
The technical implementation of this vulnerability stems from a classic buffer overflow exploit pattern where the size-remaining variable becomes corrupted through integer wrapping, causing the data pointer to extend beyond the allocated buffer boundaries. This type of flaw falls under the CWE-121 category of Stack-based Buffer Overflow, though the specific manifestation in the kernel context creates unique operational characteristics. The RXRPC subsystem, designed for remote procedure call operations, processes authentication tokens that are parsed without proper bounds checking against the assumed field sizes. When an attacker crafts a malformed Kerberos ticket with specifically calculated field dimensions, the kernel's parsing routine fails to validate the buffer boundaries properly, allowing the data pointer to traverse into adjacent memory regions.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation within the kernel space. Attackers who can influence the creation or processing of RXRPC keys through network-based attacks or local manipulation can exploit this flaw to execute arbitrary code with kernel privileges. The vulnerability's exploitation requires careful crafting of Kerberos tickets to trigger the specific buffer wrapping condition, making it moderately difficult to exploit but highly significant in terms of potential damage. This flaw directly relates to the ATT&CK technique T1068, which describes the exploitation of legitimate credentials for privilege escalation, as the vulnerability allows attackers to leverage existing authentication mechanisms to gain elevated system access. The impact is particularly severe because it affects the core kernel authentication infrastructure, potentially compromising the entire system's security posture.
Mitigation strategies for CVE-2017-7482 primarily involve upgrading to kernel versions 4.12 or later where the buffer handling logic has been corrected to properly validate field sizes and prevent integer wrapping conditions. System administrators should also implement network segmentation to limit exposure to RXRPC services and ensure that Kerberos authentication is properly configured with appropriate access controls. Additional protective measures include monitoring for unusual authentication patterns that might indicate exploitation attempts and implementing kernel hardening techniques such as stack canaries and address space layout randomization. The fix implemented in kernel 4.12 specifically addresses the field size assumption by introducing proper bounds checking and ensuring that the size-remaining variable cannot wrap under normal processing conditions, thereby preventing the memory corruption that enables privilege escalation. Organizations should prioritize this patch deployment as it addresses a fundamental security weakness in the kernel's cryptographic subsystem that could be exploited by sophisticated attackers to gain complete system control.