CVE-2024-26706 is a vulnerability identified in the Linux kernel specifically affecting the parisc architecture exception handler. The issue arises from the way the kernel's exception handler manages error codes when accessing user space memory. The handler is designed to store the error code -EFAULT into a specific register (%r29) as defined by ASM_EXCEPTIONTABLE_REG. However, if the compiler chooses to use a different register for the error code, the handler still writes -EFAULT into %r29, corrupting the data in the register actually used by the compiler. This leads to random data corruption during exception handling, particularly observed in the emulate_ldd() function. The root cause is a mismatch between the compiler's register allocation and the hardcoded register used by the fault handler to store error codes. The patch to fix this vulnerability involves extending the __ex_table by an additional 32-bit word that encodes the register chosen by the compiler for the error code. The fault handler then reads this information and correctly stores -EFAULT into the appropriate register, preventing data corruption. This approach is more flexible and reliable than the previous fixed-register assumption. However, this fix disables the BUILDTIME_TABLE_SORT configuration option due to the extended __ex_table size. This vulnerability is specific to the parisc architecture in the Linux kernel and does not affect other architectures. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

The vulnerability can cause random data corruption in kernel exception handling on parisc-based Linux systems. This corruption could lead to unpredictable kernel behavior, including potential system crashes, data integrity issues, or denial of service conditions. For European organizations running Linux on parisc architecture hardware—typically legacy or specialized systems—this could disrupt critical services or applications relying on stable kernel operations. Although parisc architecture is niche and less common in modern deployments, affected systems in industrial, research, or governmental environments could face operational instability. The data corruption could also complicate forensic analysis or debugging efforts, increasing incident response complexity. Since the vulnerability affects kernel-level exception handling, it could potentially be leveraged in combination with other vulnerabilities to escalate privileges or bypass security controls, although no direct exploit is known currently. Overall, the impact is moderate but could be significant in environments where parisc Linux systems are integral to operations.

European organizations should first identify any Linux systems running on parisc architecture, which are relatively rare and typically found in legacy or specialized environments. For these systems, applying the official Linux kernel patch that extends the __ex_table and corrects the register handling in the exception handler is critical. Since the patch disables BUILDTIME_TABLE_SORT, organizations should test the kernel build and deployment process to ensure compatibility and stability. Regular kernel updates from trusted Linux distributions should be monitored and applied promptly. Additionally, organizations should audit their systems for any signs of instability or data corruption that might indicate exploitation or manifestation of this vulnerability. Given the niche architecture, consider isolating parisc systems from critical networks or limiting their exposure to untrusted inputs. Implementing robust monitoring and logging around kernel exceptions can help detect anomalies early. Finally, maintain backups and recovery plans for affected systems to minimize downtime in case of failures related to this vulnerability.