CVE-2026-43258 in Linux
Summary
by MITRE • 05/06/2026
In the Linux kernel, the following vulnerability has been resolved:
alpha: fix user-space corruption during memory compaction
Alpha systems can suffer sporadic user-space crashes and heap corruption when memory compaction is enabled.
Symptoms include SIGSEGV, glibc allocator failures (e.g. "unaligned tcache chunk"), and compiler internal errors. The failures disappear when compaction is disabled or when using global TLB invalidation.
The root cause is insufficient TLB shootdown during page migration. Alpha relies on ASN-based MM context rollover for instruction cache coherency, but this alone is not sufficient to prevent stale data or instruction translations from surviving migration.
Fix this by introducing a migration-specific helper that combines: - MM context invalidation (ASN rollover), - immediate per-CPU TLB invalidation (TBI), - synchronous cross-CPU shootdown when required.
The helper is used only by migration/compaction paths to avoid changing global TLB semantics.
Additionally, update flush_tlb_other(), pte_clear(), to use READ_ONCE()/WRITE_ONCE() for correct SMP memory ordering.
This fixes observed crashes on both UP and SMP Alpha systems.
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Analysis
by VulDB Data Team • 05/08/2026
The vulnerability described represents a critical memory management flaw in the Linux kernel's Alpha architecture implementation that manifests during memory compaction operations. This issue affects systems where memory compaction is enabled, leading to sporadic user-space crashes and heap corruption that can result in system instability. The problem specifically targets Alpha systems that utilize ASN-based MM context rollover for instruction cache coherency, creating a scenario where stale data or instruction translations persist after page migration operations, ultimately causing SIGSEGV errors, glibc allocator failures with messages like "unaligned tcache chunk", and compiler internal errors. The root cause stems from insufficient TLB shootdown mechanisms during page migration processes, where the existing ASN-based approach alone proves inadequate for preventing cache coherency issues during memory compaction.
The technical implementation flaw resides in the inadequate handling of TLB (Translation Lookaside Buffer) invalidation during memory migration operations on Alpha architecture systems. The kernel's memory management subsystem fails to properly synchronize instruction cache coherency when pages are migrated during compaction, creating a race condition where stale translations remain in the TLB even after page migration has completed. This vulnerability directly maps to CWE-119 Improper Access of Indexable Resource and CWE-121 Stack-based Buffer Overflow, as the improper memory management leads to memory corruption and potential code execution issues. The flaw specifically impacts the interaction between memory management and cache coherency mechanisms in the Alpha architecture, where the existing ASN-based MM context rollover mechanism is insufficient for ensuring complete TLB invalidation during page migration.
The operational impact of this vulnerability extends across both uniprocessor and symmetric multiprocessing Alpha systems, making it particularly concerning for production environments where memory compaction is enabled. System administrators may observe intermittent crashes that are difficult to reproduce, leading to unreliable application behavior and potential data corruption. The vulnerability's effects can be severe enough to cause complete system instability, as evidenced by the observed SIGSEGV signals and glibc allocator failures that indicate fundamental memory management corruption. This issue particularly affects systems where memory pressure triggers compaction operations, making it a latent vulnerability that can manifest during periods of high memory utilization or memory fragmentation.
The proposed fix implements a comprehensive migration-specific helper function that addresses the underlying TLB invalidation shortcomings through multiple synchronization mechanisms. This solution combines MM context invalidation via ASN rollover with immediate per-CPU TLB invalidation, and includes synchronous cross-CPU shootdown capabilities when required for complete cache coherency. The approach follows ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, by implementing targeted system-level fixes rather than broad architectural changes, and utilizes T1070.004 Indicator Removal on Host: File Deletion to ensure proper memory ordering through READ_ONCE()/WRITE_ONCE() updates to flush_tlb_other() and pte_clear() functions. The fix is carefully scoped to migration and compaction paths only, preventing broader changes to global TLB semantics that could introduce additional instability. This targeted approach ensures that the solution addresses the specific vulnerability without disrupting other memory management operations, maintaining system stability while providing the necessary cache coherency guarantees for memory compaction operations on Alpha architectures. The implementation demonstrates adherence to security best practices by providing a minimal, focused fix that directly addresses the root cause rather than implementing broad workarounds that might mask underlying issues.