CVE-2026-74640

CVE CVE-2026-74640EUVD EUVD-2026-64577Published 2026-08-22T15:32:18.000ZLast changed 2026-08-25T05:41:01.000ZCVSS 7.8

What the advisory describes

In the Linux kernel, the following vulnerability has been resolved: ALSA: FCP: fix OOB write in fcp_meter_ctl_get() fcp_ioctl_set_meter_map() bounds the user-supplied Level Meter map size by the driver's own limit of 255 if (map.map_size < 1 || map.map_size > 255 || map.meter_slots < 1 || map.meter_slots > 255) return -EINVAL; and passes it to fcp_add_new_ctl() as the control's channel count, where it is stored as elem->channels. Every control read writes into struct snd_ctl_elem_value, whose integer array is declared long value[128], so the limit is 128, not 255. fcp_meter_ctl_get() stores one 64-bit word per channel into that array with no bound of its own: for (i = 0; i < elem->channels; i++) { int idx = private->meter_level_map[i]; int value = idx < 0 ? 0 : le32_to_cpu(resp[idx]); ucontrol->value.integer.value[i] = value; } snd_ctl_elem_read_user() serves that object from memdup_user(_control, sizeof(*control)), 1224 bytes on LP64 out of kmalloc-2048. offsetof(struct snd_ctl_elem_value, value) is 72, so element i is written at byte 72 + 8 * i and element 144 already lands past the allocation. At map_size 255 the last store ends at byte 2112, 888 bytes past the object and 64 bytes into the adjacent slab object. The stored words come from the device and meter_level_map[] selects which word lands in which slot, so extent and contents are both controlled. The core does not catch this. snd_ctl_check_elem_info() is reached only from __snd_ctl_elem_info(), which snd_ctl_elem_read() calls under CONFIG_SND_CTL_DEBUG; without that option snd_ctl_skip_validation() is a compile-time true. __snd_ctl_add_replace() validates kcontrol->count and never inspects elem->channels. Installing an oversized map needs CAP_SYS_RAWIO, but the control outlives the hwdep descriptor that created it, so the out-of-bounds stores are issued by any process able to read controls on /dev/snd/controlC0. KASAN on 7.2.0-rc5 (arm64), triggered by an unprivileged control read: BUG: KASAN: slab-out-of-bounds in fcp_meter_ctl_get Write of size 8 at addr ffff000017af04c8 by task fcp_trigger/185 __asan_store8 fcp_meter_ctl_get snd_ctl_elem_read snd_ctl_ioctl Allocated by task 185: memdup_user snd_ctl_ioctl The buggy address is located 0 bytes to the right of allocated 1224-byte region [ffff000017af0000, ffff000017af04c8) Bound the map size by the ABI limit rather than by 255, and bound the store loop at the sink so it cannot run past the value array whatever elem->channels holds. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Source: EUVD (ENISA), in the words of the advisory.

Products the advisory names

These come from the advisory itself, not from any check we performed.

• Linux — Linux 46757a3e7d50dac923888e7fbe68377736f13c70 <bb61dc2ae59026f76db26e1909746908bc5b6f31; patch: 7.2; 46757a3e7d50dac923888e7fbe68377736f13c70 <bb30e35c36ed00f24fa39aded811f64230a913b0; patch: 6.18.45; 46757a3e7d50dac923888e7fbe68377736f13c70 <620f1e52a46f604635efd0fb78138afd6a513b5d; patch: 0; patch: 7.1.9; 6.14

The versions shown are the advisory's own. Patchlage compares no version numbers and derives no judgement from them — which version is installed is something a person has to look up.

Carried in the product catalogue

An estate covering these products can be recorded in Patchlage. An advisory about them appears in the next morning's situation report.

• Linux — Linux

Patchlage reports hits and suspected hits. About everything else this system says nothing — neither this page nor the situation report ever claims that an estate is safe.