CVE-2017-18075 in Linux
Summary
by MITRE
crypto/pcrypt.c in the Linux kernel before 4.14.13 mishandles freeing instances, allowing a local user able to access the AF_ALG-based AEAD interface (CONFIG_CRYPTO_USER_API_AEAD) and pcrypt (CONFIG_CRYPTO_PCRYPT) to cause a denial of service (kfree of an incorrect pointer) or possibly have unspecified other impact by executing a crafted sequence of system calls.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability identified as CVE-2017-18075 resides within the Linux kernel's crypto subsystem, specifically in the pcrypt.c file that implements the pcrypt algorithm implementation for the AF_ALG interface. This flaw affects Linux kernel versions prior to 4.14.13 and represents a critical memory management issue that can be exploited by local users with access to the AF_ALG-based AEAD interface and pcrypt functionality. The vulnerability stems from improper handling of memory deallocation operations when freeing cryptographic instances, creating a scenario where the kernel attempts to free memory using an incorrect pointer reference.
The technical flaw manifests when the pcrypt implementation processes cryptographic operations through the AF_ALG interface, which is designed to provide userspace access to kernel crypto algorithms. When certain sequences of system calls are executed in a specific order, the kernel's memory management routines fail to properly track the memory allocation state of cryptographic instances. This results in a situation where the kfree function attempts to release memory that either has already been freed or was never properly allocated, leading to kernel memory corruption. The vulnerability is classified as a use-after-free condition that can be triggered through crafted system call sequences, making it particularly dangerous as it operates at kernel level where such flaws can lead to system instability or potential privilege escalation.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially lead to more severe consequences including system crashes, data corruption, or in some scenarios, privilege escalation depending on the exploitation vector. Local attackers with access to the AF_ALG-based AEAD interface and pcrypt configuration can leverage this flaw to disrupt system operations or potentially gain elevated privileges. The vulnerability affects systems running Linux kernel versions where both CONFIG_CRYPTO_USER_API_AEAD and CONFIG_CRYPTO_PCRYPT are enabled, which is common in many enterprise and server deployments that require advanced cryptographic capabilities. This makes the vulnerability particularly concerning as it can be exploited in environments where cryptographic operations are frequently performed and where local access is possible.
Mitigation strategies for CVE-2017-18075 primarily involve upgrading to Linux kernel version 4.14.13 or later, which contains the necessary patches to properly handle memory deallocation for cryptographic instances. System administrators should also consider disabling unnecessary cryptographic modules when they are not required, particularly the CONFIG_CRYPTO_PCRYPT configuration option if the pcrypt functionality is not needed. Additionally, monitoring systems should be implemented to detect unusual patterns of system calls related to the AF_ALG interface, as this can help identify potential exploitation attempts. From a security perspective, this vulnerability aligns with CWE-415 which describes double free conditions and CWE-416 which covers use after free errors, both of which are fundamental memory safety issues that can lead to system compromise. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques as it can potentially be leveraged to gain elevated system privileges through kernel memory corruption, making it a significant concern for security operations teams responsible for maintaining kernel security posture.