# CVE-2026-31662

> Vulnerability · severity: **HIGH** (CVSS 7.5).

## 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.

## Key facts

- **CVE ID:** CVE-2026-31662
- **Published:** 2026-04-24
- **CVSS severity:** HIGH
- **CVSS base score:** 7.5
- **CWE codes:** CWE-191

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31662

## Citation

> AI Analytics. CVE-2026-31662. Retrieved 2026-08-16 from https://api.ai-analytics.org/cve/CVE-2026-31662. Derived from NIST NVD. Licensed CC0.

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