# CVE-2026-31662: tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG

> An attacker can cause a denial of service in the Linux kernel TIPC module by sending duplicate group ACK messages, leading to a counter underflow that blocks broadcasts.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-83798, BELL-CVE-2026-31662, DEBIAN-CVE-2026-31662, GHSA-895h-4xx6-r95p, ROOT-OS-DEBIAN-11-CVE-2026-31662, ROOT-OS-DEBIAN-12-CVE-2026-31662, ROOT-OS-DEBIAN-13-CVE-2026-31662, ROOT-OS-UBUNTU-2204-CVE-2026-31662, ROOT-OS-UBUNTU-2404-CVE-2026-31662, UBUNTU-CVE-2026-31662

## What is CVE-2026-31662?

CVE-2026-31662 is a high-severity vulnerability in Linux kernel, published on 24 Apr 2026. 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:

tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG

The GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements
bc_ackers on every inbound group ACK, even when the same member has
already acknowledged the current broadcast round.

Because bc_ackers is a u16, a duplicate ACK received after the last
legitimate ACK wraps the counter to 65535. Once wrapped,
tipc_group_bc_cong() keeps reporting congestion and later group
broadcasts on the affected socket stay blocked until the group is
recreated.

Fix this by ignoring duplicate or stale ACKs before touching bc_acked or
bc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and
prevents the underflow path.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound)), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-31662?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31662?

Apply the vendor's patch.

## Is CVE-2026-31662 being exploited?

There is no known exploitation of CVE-2026-31662 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-2026-31662 and fix it if it is affected.

What it is: CVE-2026-31662 is a high-severity vulnerability in Linux kernel, published on 24 Apr 2026. 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-2026-31662 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-2026-31662/ (Markdown: https://insights.sbomify.com/CVE-2026-31662/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31662
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31662
- OSV: https://osv.dev/vulnerability/CVE-2026-31662

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31662/
Summaries are generated and may contain mistakes; the official description above is the record.