CVE-2019-19378 in Linux
Summary
by MITRE
In the Linux kernel 5.0.21, mounting a crafted btrfs filesystem image can lead to slab-out-of-bounds write access in index_rbio_pages in fs/btrfs/raid56.c.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2019-19378 represents a critical heap-based buffer overflow in the Linux kernel's btrfs filesystem implementation. This flaw exists within the index_rbio_pages function located in fs/btrfs/raid56.c, where improper bounds checking allows for out-of-bounds memory writes during the processing of crafted btrfs filesystem images. The issue specifically manifests when the kernel attempts to handle RAID56 stripe operations, creating a scenario where maliciously constructed filesystem metadata can trigger memory corruption. This vulnerability falls under the CWE-121 heap-based buffer overflow category, which is classified as a serious memory safety issue that can lead to arbitrary code execution or system crashes. The vulnerability affects Linux kernel versions up to and including 5.0.21, making it particularly concerning given the widespread adoption of these kernel versions in enterprise and server environments.
The technical exploitation of this vulnerability requires an attacker to create a specially crafted btrfs filesystem image that triggers the specific code path involving index_rbio_pages function. When the kernel mounts such a filesystem, the flawed memory handling causes a slab allocator out-of-bounds write operation, potentially corrupting adjacent memory regions in the kernel's heap. This type of vulnerability is particularly dangerous because it can be leveraged for privilege escalation attacks, allowing unprivileged users to execute arbitrary code with kernel privileges. The ATT&CK framework categorizes this as a privilege escalation technique through kernel memory corruption, specifically mapping to T1068 which involves exploiting vulnerabilities in operating system kernels. The vulnerability's impact is amplified by the fact that btrfs is a widely deployed filesystem in Linux environments, particularly in server and storage applications where the ability to mount arbitrary filesystem images might be possible through various attack vectors.
The operational impact of CVE-2019-19378 extends beyond simple system instability to potential complete system compromise. When exploited successfully, this vulnerability can lead to privilege escalation from unprivileged user to root level access, enabling attackers to gain complete control over affected systems. The memory corruption can result in kernel crashes, data corruption, or more sinisterly, provide a foothold for persistent backdoor installation. Organizations running Linux systems with kernel versions 5.0.21 or earlier are particularly at risk, as the vulnerability can be triggered through legitimate filesystem mounting operations. The exploitability of this vulnerability is enhanced by the fact that btrfs filesystems can be mounted by users with appropriate permissions, making it possible for attackers to construct malicious images and mount them on vulnerable systems. This creates a scenario where even a simple file transfer or system mount operation could result in system compromise, making the vulnerability particularly dangerous in multi-user or shared hosting environments. The vulnerability also impacts containerized environments where btrfs is used for storage backends, potentially allowing container escape attacks that could compromise entire host systems.
Mitigation strategies for CVE-2019-19378 primarily involve upgrading to patched kernel versions where the vulnerability has been addressed through proper bounds checking in the index_rbio_pages function. System administrators should prioritize kernel updates to versions that include the fix, which typically involves implementing additional validation checks for buffer sizes and proper memory boundary enforcement. Additionally, implementing filesystem access controls and restricting user mount capabilities can help reduce the attack surface, though this approach does not eliminate the vulnerability entirely. Network segmentation and monitoring for suspicious filesystem mounting activities can provide early detection of potential exploitation attempts. The fix implemented in patched kernels addresses the root cause by ensuring proper bounds checking before memory operations, preventing the slab allocator from writing beyond allocated memory regions. Organizations should also consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and kernel module signing to further reduce the exploitability of similar vulnerabilities. Regular security audits and vulnerability assessments should include checks for outdated kernel versions that may be susceptible to this and related memory corruption vulnerabilities.