# CVE-2026-45990: slub: fix data loss and overflow in krealloc()

> An integer overflow in the Linux kernel's krealloc function allows out-of-bounds writes, potentially leading to code execution or privilege escalation.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 27 May 2026
- **Updated:** 14 Jun 2026
- **Also known as:** BELL-CVE-2026-45990, DEBIAN-CVE-2026-45990, GHSA-q4r9-vxp8-26x5, UBUNTU-CVE-2026-45990

## What is CVE-2026-45990?

CVE-2026-45990 is a medium-severity vulnerability in Linux kernel, published on 27 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:

slub: fix data loss and overflow in krealloc()

Commit 2cd8231796b5 ("mm/slub: allow to set node and align in
k[v]realloc") introduced the ability to force a reallocation if the
original object does not satisfy new alignment or NUMA node, even when
the object is being shrunk.

This introduced two bugs in the reallocation fallback path:

1. Data loss during NUMA migration: The jump to 'alloc_new' happens
   before 'ks' and 'orig_size' are initialized. As a result, the
   memcpy() in the 'alloc_new' block would copy 0 bytes into the new
   allocation.

2. Buffer overflow during shrinking: When shrinking an object while
   forcing a new alignment, 'new_size' is smaller than the old size.
   However, the memcpy() used the old size ('orig_size ?: ks'), leading
   to an out-of-bounds write.

The same overflow bug exists in the kvrealloc() fallback path, where the
old bucket size ksize(p) is copied into the new buffer without being
bounded by the new size.

A simple reproducer:

	// e.g. add to lkdtm as KREALLOC_SHRINK_OVERFLOW
	while (1) {
		void *p = kmalloc(128, GFP_KERNEL);
		p = krealloc_node_align(p, 64, 256, GFP_KERNEL, NUMA_NO_NODE);
		kfree(p);
	}

demonstrates the issue:

  ==================================================================
  BUG: KFENCE: out-of-bounds write in memcpy_orig+0x68/0x130

  Out-of-bounds write at 0xffff8883ad757038 (120B right of kfence-#47):
   memcpy_orig+0x68/0x130
   krealloc_node_align_noprof+0x1c8/0x340
   lkdtm_KREALLOC_SHRINK_OVERFLOW+0x8c/0xc0 [lkdtm]
   lkdtm_do_action+0x3a/0x60 [lkdtm]
   ...

  kfence-#47: 0xffff8883ad756fc0-0xffff8883ad756fff, size=64, cache=kmalloc-64

  allocated by task 316 on cpu 7 at 97.680481s (0.021813s ago):
   krealloc_node_align_noprof+0x19c/0x340
   lkdtm_KREALLOC_SHRINK_OVERFLOW+0x8c/0xc0 [lkdtm]
   lkdtm_do_action+0x3a/0x60 [lkdtm]
   ...
  ==================================================================

Fix it by moving the old size calculation to the top of __do_krealloc()
and bounding all copy lengths by the new allocation size.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-45990?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45990?

Apply the vendor's patch.

## Is CVE-2026-45990 being exploited?

There is no known exploitation of CVE-2026-45990 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-2026-45990 and fix it if it is affected.

What it is: CVE-2026-45990 is a medium-severity vulnerability in Linux kernel, published on 27 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-2026-45990 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-2026-45990/ (Markdown: https://insights.sbomify.com/CVE-2026-45990/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45990
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45990
- OSV: https://osv.dev/vulnerability/CVE-2026-45990

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45990/
Summaries are generated and may contain mistakes; the official description above is the record.