# CVE-2025-40281: sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto

> A shift-out-of-bounds error in the Linux kernel SCTP implementation allows remote attackers to cause a denial of service via crafted network packets.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Dec 2025
- **Updated:** 16 Jun 2026
- **Also known as:** BELL-CVE-2025-40281, DEBIAN-CVE-2025-40281, GHSA-mgqw-v2hw-3wq7, ROOT-OS-DEBIAN-12-CVE-2025-40281, ROOT-OS-DEBIAN-13-CVE-2025-40281, ROOT-OS-UBUNTU-2204-CVE-2025-40281, ROOT-OS-UBUNTU-2404-CVE-2025-40281, UBUNTU-CVE-2025-40281

## What is CVE-2025-40281?

CVE-2025-40281 is a vulnerability in Linux, published on 6 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto

syzbot reported a possible shift-out-of-bounds [1]

Blamed commit added rto_alpha_max and rto_beta_max set to 1000.

It is unclear if some sctp users are setting very large rto_alpha
and/or rto_beta.

In order to prevent user regression, perform the test at run time.

Also add READ_ONCE() annotations as sysctl values can change under us.

[1]

UBSAN: shift-out-of-bounds in net/sctp/transport.c:509:41
shift exponent 64 is too large for 32-bit type 'unsigned int'
CPU: 0 UID: 0 PID: 16704 Comm: syz.2.2320 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
  __dump_stack lib/dump_stack.c:94 [inline]
  dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
  ubsan_epilogue lib/ubsan.c:233 [inline]
  __ubsan_handle_shift_out_of_bounds+0x27f/0x420 lib/ubsan.c:494
  sctp_transport_update_rto.cold+0x1c/0x34b net/sctp/transport.c:509
  sctp_check_transmitted+0x11c4/0x1c30 net/sctp/outqueue.c:1502
  sctp_outq_sack+0x4ef/0x1b20 net/sctp/outqueue.c:1338
  sctp_cmd_process_sack net/sctp/sm_sideeffect.c:840 [inline]
  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1372 [inline]

## Which versions are affected by CVE-2025-40281?


## How do I fix CVE-2025-40281?

Apply the vendor's patch.

## Is CVE-2025-40281 being exploited?

There is no known exploitation of CVE-2025-40281 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40281 and fix it if it is affected.

What it is: CVE-2025-40281 is a vulnerability in Linux, published on 6 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40281 in the wild and no public exploit code.

Affected product: Linux. 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-2025-40281/ (Markdown: https://insights.sbomify.com/CVE-2025-40281/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40281
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40281
- OSV: https://osv.dev/vulnerability/CVE-2025-40281

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40281/
Summaries are generated and may contain mistakes; the official description above is the record.