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

> Insufficient TLB shootdown during memory compaction on Alpha systems causes user-space memory corruption, leading to crashes or potential code execution.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-85863, BELL-CVE-2026-43258, DEBIAN-CVE-2026-43258, GHSA-rj9j-qfgp-687w, ROOT-OS-DEBIAN-11-CVE-2026-43258, ROOT-OS-DEBIAN-12-CVE-2026-43258, ROOT-OS-UBUNTU-2204-CVE-2026-43258, ROOT-OS-UBUNTU-2404-CVE-2026-43258, UBUNTU-CVE-2026-43258

## What is CVE-2026-43258?

CVE-2026-43258 is a high-severity memory corruption vulnerability in Linux kernel, published on 6 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-43258?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43258?

Apply the vendor's patch.

## Is CVE-2026-43258 being exploited?

There is no known exploitation of CVE-2026-43258 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43258 and fix it if it is affected.

What it is: CVE-2026-43258 is a high-severity memory corruption vulnerability in Linux kernel, published on 6 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43258 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43258/ (Markdown: https://insights.sbomify.com/CVE-2026-43258/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43258
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43258
- OSV: https://osv.dev/vulnerability/CVE-2026-43258

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43258/
Summaries are generated and may contain mistakes; the official description above is the record.