CVE-2018-19854 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel before 4.19.3. crypto_report_one() and related functions in crypto/crypto_user.c (the crypto user configuration API) do not fully initialize structures that are copied to userspace, potentially leaking sensitive memory to user programs. NOTE: this is a CVE-2013-2547 regression but with easier exploitability because the attacker does not need a capability (however, the system must have the CONFIG_CRYPTO_USER kconfig option).
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-19854 represents a critical information disclosure flaw in the Linux kernel affecting versions prior to 4.19.3. This issue manifests within the crypto user configuration API through the crypto_report_one() function and related implementations located in the crypto/crypto_user.c file. The flaw stems from incomplete initialization of kernel structures before they are copied to userspace, creating a scenario where sensitive kernel memory contents can be inadvertently exposed to unprivileged user programs. This regression from the previously addressed CVE-2013-2547 maintains the core vulnerability but reduces the attack prerequisites, making it more exploitable in certain environments.
The technical implementation of this vulnerability involves the improper handling of memory structures within the kernel's cryptographic subsystem. When crypto_report_one() and associated functions process cryptographic algorithm reports, they fail to completely zero out or initialize the structures before copying them to userspace. This incomplete initialization leaves residual data from kernel memory, potentially including cryptographic keys, internal kernel pointers, or other sensitive information, accessible to user-level applications. The vulnerability specifically requires the CONFIG_CRYPTO_USER kernel configuration option to be enabled, which provides the user-space interface for cryptographic operations but also exposes this information disclosure channel.
The operational impact of CVE-2018-19854 extends beyond simple information leakage, as the exposed kernel memory may contain critical cryptographic material that could aid in more sophisticated attacks. An attacker exploiting this vulnerability could potentially recover cryptographic keys, internal kernel data structures, or other sensitive information that might be used to bypass security controls or facilitate further exploitation. The vulnerability is particularly concerning in environments where cryptographic operations are frequently performed and where unprivileged users might have access to the system. The reduced exploitability requirements compared to CVE-2013-2547 mean that attackers no longer need specific capabilities to leverage this flaw, making it more accessible to a broader range of threat actors.
Mitigation strategies for this vulnerability primarily involve upgrading to kernel versions 4.19.3 or later where the issue has been addressed through proper structure initialization. System administrators should also consider disabling the CONFIG_CRYPTO_USER configuration option if the cryptographic user interface is not required, as this eliminates the attack surface entirely. Additionally, implementing proper access controls and monitoring for unusual cryptographic operations can help detect potential exploitation attempts. This vulnerability aligns with CWE-248, an information exposure weakness, and could be categorized under ATT&CK technique T1059 for execution through system commands, particularly when exploited to gain access to sensitive kernel memory contents. Organizations should prioritize patch management and kernel updates to remediate this vulnerability and maintain system security posture.