# CVE-2026-31774: io_uring/net: fix slab-out-of-bounds read in io_bundle_nbufs()

> A local attacker can trigger an integer overflow in the Linux kernel's io_uring subsystem, causing a slab-out-of-bounds read and potential system crash or memory leak.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 1 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-31774, DEBIAN-CVE-2026-31774, GHSA-w3xc-h2ch-2q3q, UBUNTU-CVE-2026-31774

## What is CVE-2026-31774?

CVE-2026-31774 is a high-severity vulnerability in Linux kernel, published on 1 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:

io_uring/net: fix slab-out-of-bounds read in io_bundle_nbufs()

sqe->len is __u32 but gets stored into sr->len which is int. When
userspace passes sqe->len values exceeding INT_MAX (e.g. 0xFFFFFFFF),
sr->len overflows to a negative value. This negative value propagates
through the bundle recv/send path:

  1. io_recv(): sel.val = sr->len (ssize_t gets -1)
  2. io_recv_buf_select(): arg.max_len = sel->val (size_t gets
     0xFFFFFFFFFFFFFFFF)
  3. io_ring_buffers_peek(): buf->len is not clamped because max_len
     is astronomically large
  4. iov[].iov_len = 0xFFFFFFFF flows into io_bundle_nbufs()
  5. io_bundle_nbufs(): min_t(int, 0xFFFFFFFF, ret) yields -1,
     causing ret to increase instead of decrease, creating an
     infinite loop that reads past the allocated iov[] array

This results in a slab-out-of-bounds read in io_bundle_nbufs() from
the kmalloc-64 slab, as nbufs increments past the allocated iovec
entries.

  BUG: KASAN: slab-out-of-bounds in io_bundle_nbufs+0x128/0x160
  Read of size 8 at addr ffff888100ae05c8 by task exp/145
  Call Trace:
   io_bundle_nbufs+0x128/0x160
   io_recv_finish+0x117/0xe20
   io_recv+0x2db/0x1160

Fix this by rejecting negative sr->len values early in both
io_sendmsg_prep() and io_recvmsg_prep(). Since sqe->len is __u32,
any value > INT_MAX indicates overflow and is not a valid length.

Weakness: CWE-125 (Out-of-bounds Read), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-31774?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31774?

Apply the vendor's patch.

## Is CVE-2026-31774 being exploited?

There is no known exploitation of CVE-2026-31774 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-2026-31774 and fix it if it is affected.

What it is: CVE-2026-31774 is a high-severity vulnerability in Linux kernel, published on 1 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-2026-31774 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-2026-31774/ (Markdown: https://insights.sbomify.com/CVE-2026-31774/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31774
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31774
- OSV: https://osv.dev/vulnerability/CVE-2026-31774

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31774/
Summaries are generated and may contain mistakes; the official description above is the record.