CVE-2026-64029 - Vulnerability Details

- ALSA: seq: Serialize UMP output teardown with event_input

Description

In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: Serialize UMP output teardown with event_input

seq_ump_process_event() borrows client->out_rfile.output without
synchronizing with the first-open and last-close transition in
seq_ump_client_open() and seq_ump_client_close().

The last output unuse can therefore drop opened[STR_OUT] to zero and
release the rawmidi file while an in-flight event_input callback is still
inside snd_rawmidi_kernel_write(). That leaves the rawmidi substream
runtime exposed to teardown before the write path has taken its own
buffer reference.

Add a per-client rwlock for the event_input-visible output file. Publish
a newly opened output file under the write side, and hold the read side
from the output lookup through snd_rawmidi_kernel_write(). The last
output close copies and clears the visible output file under the write
side, then drops the lock and releases the saved rawmidi file. Use
IRQ-safe rwlock guards because event_input can also be reached from
atomic sequencer delivery.

The buggy scenario involves two paths, with each column showing the
order within that path:

path A label: event_input path path B label: last unuse path
1. seq_ump_process_event() reads 1. seq_ump_client_close()
client->out_rfile.output. drops opened[STR_OUT] to zero.
2. snd_rawmidi_kernel_write1() 2. snd_rawmidi_kernel_release()
has not yet pinned runtime. closes the output file.
3. The writer continues using 3. close_substream() frees
the borrowed substream. substream->runtime.

This keeps the output substream and runtime alive for the full
event_input write while keeping rawmidi release outside the rwlock.

KASAN reproduced this as a slab-use-after-free in
snd_rawmidi_kernel_write1(), with allocation through
seq_ump_use()/snd_seq_port_connect() and free through
seq_ump_unuse()/snd_seq_port_disconnect().

Validation reproduced this kernel report:
KASAN slab-use-after-free in snd_rawmidi_kernel_write1+0x9d/0x400
RIP: 0033:0x7f5528af837f
Read of size 8
Call trace:
dump_stack_lvl+0x73/0xb0 (?:?)
print_report+0xd1/0x650 (?:?)
srso_alias_return_thunk+0x5/0xfbef5 (?:?)
__virt_addr_valid+0x1a7/0x340 (?:?)
kasan_complete_mode_report_info+0x64/0x200 (?:?)
kasan_report+0xf7/0x130 (?:?)
snd_rawmidi_kernel_write1+0x9d/0x400 (?:?)
__asan_load8+0x82/0xb0 (?:?)
update_stack_state+0x1ef/0x2d0 (?:?)
snd_rawmidi_kernel_write+0x1a/0x20 (?:?)
seq_ump_process_event+0xd4/0x120 (sound/core/seq/seq_ump_client.c:82)
__snd_seq_deliver_single_event+0x8a/0xe0 (?:?)
snd_seq_deliver_from_ump+0x2b2/0xd60 (?:?)
lock_acquire+0x14e/0x2e0 (?:?)
find_held_lock+0x31/0x90 (?:?)
snd_seq_port_use_ptr+0xa6/0xe0 (?:?)
__kasan_check_write+0x18/0x20 (?:?)
do_raw_read_unlock+0x32/0xa0 (?:?)
_raw_read_unlock+0x26/0x50 (?:?)
snd_seq_deliver_single_event+0x45c/0x4b0 (?:?)
snd_seq_deliver_event+0x10d/0x1b0 (?:?)
snd_seq_client_enqueue_event+0x192/0x240 (?:?)
snd_seq_write+0x2cd/0x450 (?:?)
apparmor_file_permission+0x20/0x30 (?:?)
security_file_permission+0x51/0x60 (?:?)
vfs_write+0x1ce/0x850 (?:?)
__fget_files+0x12b/0x220 (?:?)
lock_release+0xc8/0x2a0 (?:?)
__rcu_read_unlock+0x74/0x2d0 (?:?)
__fget_files+0x135/0x220 (?:?)
ksys_write+0x15a/0x180 (?:?)
rcu_is_watching+0x24/0x60 (?:?)
__x64_sys_write+0x46/0x60 (?:?)
x64_sys_call+0x7d/0x20d0 (?:?)
do_syscall_64+0xc1/0x360 (arch/x86/entry/syscall_64.c:87)
entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)

Published: 2026-07-19

Score: 7.8 High

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

The vulnerability is a race condition that leads to a use‑after‑free in the ALSA sequencer UMP output teardown path. Two execution paths allow the rawmidi substream runtime to be freed while a write callback is still executing, causing a kernel crash and a potential denial of service. The flaw is a classic race condition leading to a use‑after‑free (CWE‑364).

Affected Systems

The Linux kernel ALSA sequencer module is affected. All kernel releases that include the ALSA seq component prior to the commit that added an event_input‑visible output lock are vulnerable. No specific vendor or version list is supplied aside from Linux kernel.

Risk and Exploitability

The CVSS score of 7.8 indicates high severity. The EPSS score is below 1% and the vulnerability is not listed in CISA KEV, suggesting limited public exploitation. Based on the description, it is inferred that an attacker would need to trigger an ALSA event_input while the client is concurrently closing the output file, which requires privilege to run applications that use the ALSA sequencer or to control audio devices. If successful, the kernel crash would deny service to the system. The lack of an active KEV listing does not eliminate risk but indicates a lower current exploitation probability.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`81fd444aa371261cd33f31d4ffd80faeeeab0cc9`	affected	< 8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb
`81fd444aa371261cd33f31d4ffd80faeeeab0cc9`	affected	< 0cb1ad795570167558530d6194297ac2396a1991
`81fd444aa371261cd33f31d4ffd80faeeeab0cc9`	affected	< 3aab4a58d23fb22dac5b558bbe5df1a8dad00b4b
`81fd444aa371261cd33f31d4ffd80faeeeab0cc9`	affected	< ef46b616a4c219185bbf10ebcbacb571583fd0e4
`81fd444aa371261cd33f31d4ffd80faeeeab0cc9`	affected	< 60a1969fae6209644698fca91c185d153674f631

Linux

affected

Version	Status	Constraints
`6.5`	affected	—
`0`	unaffected	< 6.5
`6.6.142`	unaffected	≤ 6.6.*
`6.12.92`	unaffected	≤ 6.12.*
`6.18.34`	unaffected	≤ 6.18.*
`7.0.11`	unaffected	≤ 7.0.*
`7.1`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[81fd444aa371261cd33f31d4ffd80faeeeab0cc9,8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb)`	affected	code_commit	—
`[81fd444aa371261cd33f31d4ffd80faeeeab0cc9,0cb1ad795570167558530d6194297ac2396a1991)`	affected	code_commit	—
`[81fd444aa371261cd33f31d4ffd80faeeeab0cc9,3aab4a58d23fb22dac5b558bbe5df1a8dad00b4b)`	affected	code_commit	—
`[81fd444aa371261cd33f31d4ffd80faeeeab0cc9,ef46b616a4c219185bbf10ebcbacb571583fd0e4)`	affected	code_commit	—
`[81fd444aa371261cd33f31d4ffd80faeeeab0cc9,60a1969fae6209644698fca91c185d153674f631)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`6.5`	affected	generic	—
`[0,6.5)`	unaffected	generic	—
`[6.6.142,6.7.0)`	unaffected	semver	—
`[6.12.92,6.13.0)`	unaffected	semver	—
`[6.18.34,6.19.0)`	unaffected	semver	—
`[7.0.11,7.1.0)`	unaffected	semver	—
`[7.1,*]`	unaffected	generic	—

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Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

Update the kernel to a version that includes the patch adding a per-client rwlock for the event_input‑visible output file, such as the commit series after 0cb1ad7 or 3aab4a5.
If a kernel upgrade is not immediately possible, disable or restrict the ALSA sequencer subsystem for untrusted processes, or unload the ALSA seq module from the running kernel if the subsystem is not required.
Monitor system logs for KASAN or BUG reports referencing ‘use‑after‑free’ in snd_rawmidi_kernel_write1 to detect undetected failures before a full crash occurs.

Generated by OpenCVE AI on August 4, 2026 at 06:09 UTC.

Tracking

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Advisories

Source	ID	Title
Ubuntu USN	USN-8593-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8603-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8618-1	Linux kernel vulnerabilities

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00125.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/0cb1ad795570167558530d6194297ac2396a1991
https://git.kernel.org/stable/c/3aab4a58d23fb22dac5b558bbe5df1a8dad00b4b
https://git.kernel.org/stable/c/60a1969fae6209644698fca91c185d153674f631
https://git.kernel.org/stable/c/8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb
https://git.kernel.org/stable/c/ef46b616a4c219185bbf10ebcbacb571583fd0e4
https://lore.kernel.org/linux-cve-announce/2026071903-CVE-2026-64029-4b58@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-64029
https://www.cve.org/CVERecord?id=CVE-2026-64029

History

Wed, 22 Jul 2026 12:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-364
References		https://lore.kernel.org/linux-cve-announce/2026071903-CVE-2026-64029-4b58@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-64029 https://www.cve.org/CVERecord?id=CVE-2026-64029
Metrics	threat_severity `None`	threat_severity `Moderate`

Mon, 20 Jul 2026 14:45:00 +0000

Type	Values Removed	Values Added
Metrics		cvssV3_1 `{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}`

Sun, 19 Jul 2026 15:45:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: Serialize UMP output teardown with event_input seq_ump_process_event() borrows client->out_rfile.output without synchronizing with the first-open and last-close transition in seq_ump_client_open() and seq_ump_client_close(). The last output unuse can therefore drop opened[STR_OUT] to zero and release the rawmidi file while an in-flight event_input callback is still inside snd_rawmidi_kernel_write(). That leaves the rawmidi substream runtime exposed to teardown before the write path has taken its own buffer reference. Add a per-client rwlock for the event_input-visible output file. Publish a newly opened output file under the write side, and hold the read side from the output lookup through snd_rawmidi_kernel_write(). The last output close copies and clears the visible output file under the write side, then drops the lock and releases the saved rawmidi file. Use IRQ-safe rwlock guards because event_input can also be reached from atomic sequencer delivery. The buggy scenario involves two paths, with each column showing the order within that path: path A label: event_input path path B label: last unuse path 1. seq_ump_process_event() reads 1. seq_ump_client_close() client->out_rfile.output. drops opened[STR_OUT] to zero. 2. snd_rawmidi_kernel_write1() 2. snd_rawmidi_kernel_release() has not yet pinned runtime. closes the output file. 3. The writer continues using 3. close_substream() frees the borrowed substream. substream->runtime. This keeps the output substream and runtime alive for the full event_input write while keeping rawmidi release outside the rwlock. KASAN reproduced this as a slab-use-after-free in snd_rawmidi_kernel_write1(), with allocation through seq_ump_use()/snd_seq_port_connect() and free through seq_ump_unuse()/snd_seq_port_disconnect(). Validation reproduced this kernel report: KASAN slab-use-after-free in snd_rawmidi_kernel_write1+0x9d/0x400 RIP: 0033:0x7f5528af837f Read of size 8 Call trace: dump_stack_lvl+0x73/0xb0 (?:?) print_report+0xd1/0x650 (?:?) srso_alias_return_thunk+0x5/0xfbef5 (?:?) __virt_addr_valid+0x1a7/0x340 (?:?) kasan_complete_mode_report_info+0x64/0x200 (?:?) kasan_report+0xf7/0x130 (?:?) snd_rawmidi_kernel_write1+0x9d/0x400 (?:?) __asan_load8+0x82/0xb0 (?:?) update_stack_state+0x1ef/0x2d0 (?:?) snd_rawmidi_kernel_write+0x1a/0x20 (?:?) seq_ump_process_event+0xd4/0x120 (sound/core/seq/seq_ump_client.c:82) __snd_seq_deliver_single_event+0x8a/0xe0 (?:?) snd_seq_deliver_from_ump+0x2b2/0xd60 (?:?) lock_acquire+0x14e/0x2e0 (?:?) find_held_lock+0x31/0x90 (?:?) snd_seq_port_use_ptr+0xa6/0xe0 (?:?) __kasan_check_write+0x18/0x20 (?:?) do_raw_read_unlock+0x32/0xa0 (?:?) _raw_read_unlock+0x26/0x50 (?:?) snd_seq_deliver_single_event+0x45c/0x4b0 (?:?) snd_seq_deliver_event+0x10d/0x1b0 (?:?) snd_seq_client_enqueue_event+0x192/0x240 (?:?) snd_seq_write+0x2cd/0x450 (?:?) apparmor_file_permission+0x20/0x30 (?:?) security_file_permission+0x51/0x60 (?:?) vfs_write+0x1ce/0x850 (?:?) __fget_files+0x12b/0x220 (?:?) lock_release+0xc8/0x2a0 (?:?) __rcu_read_unlock+0x74/0x2d0 (?:?) __fget_files+0x135/0x220 (?:?) ksys_write+0x15a/0x180 (?:?) rcu_is_watching+0x24/0x60 (?:?) __x64_sys_write+0x46/0x60 (?:?) x64_sys_call+0x7d/0x20d0 (?:?) do_syscall_64+0xc1/0x360 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
Title		ALSA: seq: Serialize UMP output teardown with event_input
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/0cb1ad795570167558530d6194297ac2396a1991 https://git.kernel.org/stable/c/3aab4a58d23fb22dac5b558bbe5df1a8dad00b4b https://git.kernel.org/stable/c/60a1969fae6209644698fca91c185d153674f631 https://git.kernel.org/stable/c/8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb https://git.kernel.org/stable/c/ef46b616a4c219185bbf10ebcbacb571583fd0e4

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-07-19T15:39:20.368Z

Updated: 2026-08-05T12:38:23.130Z

Reserved: 2026-07-19T07:54:57.028Z

Link: CVE-2026-64029

Vulnrichment

No data.

NVD

No data.

Redhat

Severity : Moderate

Publid Date: 2026-07-19T00:00:00Z

Links: CVE-2026-64029 - Bugzilla

OpenCVE Enrichment

Updated: 2026-08-04T06:15:04Z

Weaknesses

CWE-364
Signal Handler Race Condition

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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