CVE-2026-74388 - Vulnerability Details

- ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data

Description

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

ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data

The OSS sequencer processes the input MIDI bytes into a sequencer
event to be dispatched later (in snd_seq_oss_midi_putc() called from
snd_seq_oss_process_event()). When it's a SysEx data, the event
record contains data.ext.ptr pointer to the original SysEx bytes, and
the referred data is copied into the pool afterwards at dispatching.
The problem is that, if the sequencer port gets closed concurrently
before the dispatch, the OSS sequencer core also releases the
resources (in snd_seq_oss_midi_check_exit_port()), while the pending
event may hold a stale pointer, eventually leading to a UAF at a later
dispatch.

Fortunately, there is already a refcounting mechanism (snd_use_lock_t)
for the OSS MIDI device access, and for addressing the issue above, we
just need to extend the refcount until the event gets dispatched.

This patch extends snd_seq_oss_process_event() to give back the
refcount object, which is in turn released after calling the sequencer
dispatcher with the given event in the caller side.

According to the original report, KASAN report as below:

KASAN slab-use-after-free in snd_seq_event_dup+0x40c/0x470
RIP: 0033:0x7f2cb66a6340
Read of size 6
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_seq_event_dup+0x40c/0x470 (?:?)
kasan_check_range+0x10c/0x1c0 (?:?)
__asan_memcpy+0x27/0x70 (?:?)
snd_seq_event_dup+0x9/0x470 (?:?)
snd_seq_client_enqueue_event+0x139/0x240 (?:?)
_raw_spin_unlock_irqrestore+0x4b/0x60 (?:?)
snd_seq_kernel_client_enqueue+0x102/0x120 (?:?)
snd_seq_oss_write+0x416/0x4e0 (?:?)
apparmor_file_permission+0x20/0x30 (?:?)
odev_write+0x3b/0x60 (?:?)
vfs_write+0x1ce/0x850 (?:?)
lock_release+0xc8/0x2a0 (?:?)
__kasan_check_write+0x18/0x20 (?:?)
__mutex_unlock_slowpath+0x129/0x510 (?:?)
ksys_write+0xe1/0x180 (?:?)
mutex_unlock+0x16/0x20 (?:?)
odev_ioctl+0x65/0xc0 (?:?)
__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: 2026-08-15

Score: 7.8 High

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

The flaw originates in the ALSA OSS sequencer of the Linux kernel during the processing of SysEx MIDI events. When a SysEx event is queued, the sequencer stores the original SysEx data in an event record. If the associated sequencer port is closed before the event is dispatched, the OSS core frees the original buffer while the queued event still holds a pointer to it. When the queued event is later dispatched, the stale pointer is dereferenced, producing a use‑after‑free condition in kernel memory. The KASAN report shows a slab-use‑after‑free in snd_seq_event_dup, indicating that kernel memory may be read after it has been freed.

Affected Systems

The vulnerability is present in all Linux kernel versions that include the ALSA OSS sequencer component and have not yet applied the patch that extends the reference count during event processing. Because no specific kernel release numbers are listed, any older kernel that shipped the unpatched ALSA OSS sequencer is potentially affected, including standard distributions that ship a kernel with the OSS sequencer enabled.

Risk and Exploitability

The CVSS score is 7.8, and the EPSS score is below 1%, suggesting a low likelihood of exploitation, and the vulnerability is not listed in the CISA KEV catalog. However, a successful exploitation of a kernel‑mode use‑after‑free can lead to memory corruption, kernel panic, or denial of service. The ability to trigger the flaw requires the attacker to supply a SysEx payload to the target system, which is typically possible for a local user or an application that has access to audio I/O, or from a connected MIDI device. This attack vector inference is based on the description of how the flaw is triggered, and is not explicitly stated in the official advisory.

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
`1da177e4c3f41524e886b7f1b8a0c1fc7321cac2`	affected	< 6dc781778b595be94c31395b2cb167f65145d91f
`1da177e4c3f41524e886b7f1b8a0c1fc7321cac2`	affected	< 7aad70cabd8f34cf11a9593fcd3f2ac3f5496943
`1da177e4c3f41524e886b7f1b8a0c1fc7321cac2`	affected	< 7c349b4f2a603202fb8c363bd2774a22ac2fddf3

Linux

affected

Version	Status	Constraints
`2.6.12`	affected	—
`0`	unaffected	< 2.6.12
`6.18.40`	unaffected	≤ 6.18.*
`7.1.5`	unaffected	≤ 7.1.*
`7.2`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,6dc781778b595be94c31395b2cb167f65145d91f)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,7aad70cabd8f34cf11a9593fcd3f2ac3f5496943)`	affected	code_commit	—
`[1da177e4c3f41524e886b7f1b8a0c1fc7321cac2,7c349b4f2a603202fb8c363bd2774a22ac2fddf3)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`2.6.12`	affected	semver	—
`[0,2.6.12)`	unaffected	semver	—
`[6.18.40,6.19.0)`	unaffected	semver	—
`[7.1.5,7.2.0)`	unaffected	semver	—
`[7.2-rc1,*]`	unaffected	generic	—

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Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

Install the latest Linux kernel release that incorporates the ALSA OSS sequencer patch from the distribution maintainers
If immediate updating is not feasible, disable the OSS sequencer driver via kernel configuration or module loading options to eliminate the vulnerable code path
Apply access restrictions to the ALSA sequencer interface, ensuring only trusted users or processes can send SysEx data

Generated by OpenCVE AI on August 21, 2026 at 23:37 UTC.

Tracking

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Advisories

No advisories yet.

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 0.00124.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/6dc781778b595be94c31395b2cb167f65145d91f
https://git.kernel.org/stable/c/7aad70cabd8f34cf11a9593fcd3f2ac3f5496943
https://git.kernel.org/stable/c/7c349b4f2a603202fb8c363bd2774a22ac2fddf3
https://lore.kernel.org/linux-cve-announce/2026081506-CVE-2026-74388-e1a2@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-74388
https://www.cve.org/CVERecord?id=CVE-2026-74388

History

Fri, 21 Aug 2026 00:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-825
References		https://lore.kernel.org/linux-cve-announce/2026081506-CVE-2026-74388-e1a2@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-74388 https://www.cve.org/CVERecord?id=CVE-2026-74388
Metrics	threat_severity `None`	threat_severity `Moderate`

Mon, 17 Aug 2026 12:30:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-416

Mon, 17 Aug 2026 06:00:00 +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'}`

Sat, 15 Aug 2026 06:15:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data The OSS sequencer processes the input MIDI bytes into a sequencer event to be dispatched later (in snd_seq_oss_midi_putc() called from snd_seq_oss_process_event()). When it's a SysEx data, the event record contains data.ext.ptr pointer to the original SysEx bytes, and the referred data is copied into the pool afterwards at dispatching. The problem is that, if the sequencer port gets closed concurrently before the dispatch, the OSS sequencer core also releases the resources (in snd_seq_oss_midi_check_exit_port()), while the pending event may hold a stale pointer, eventually leading to a UAF at a later dispatch. Fortunately, there is already a refcounting mechanism (snd_use_lock_t) for the OSS MIDI device access, and for addressing the issue above, we just need to extend the refcount until the event gets dispatched. This patch extends snd_seq_oss_process_event() to give back the refcount object, which is in turn released after calling the sequencer dispatcher with the given event in the caller side. According to the original report, KASAN report as below: KASAN slab-use-after-free in snd_seq_event_dup+0x40c/0x470 RIP: 0033:0x7f2cb66a6340 Read of size 6 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_seq_event_dup+0x40c/0x470 (?:?) kasan_check_range+0x10c/0x1c0 (?:?) __asan_memcpy+0x27/0x70 (?:?) snd_seq_event_dup+0x9/0x470 (?:?) snd_seq_client_enqueue_event+0x139/0x240 (?:?) _raw_spin_unlock_irqrestore+0x4b/0x60 (?:?) snd_seq_kernel_client_enqueue+0x102/0x120 (?:?) snd_seq_oss_write+0x416/0x4e0 (?:?) apparmor_file_permission+0x20/0x30 (?:?) odev_write+0x3b/0x60 (?:?) vfs_write+0x1ce/0x850 (?:?) lock_release+0xc8/0x2a0 (?:?) __kasan_check_write+0x18/0x20 (?:?) __mutex_unlock_slowpath+0x129/0x510 (?:?) ksys_write+0xe1/0x180 (?:?) mutex_unlock+0x16/0x20 (?:?) odev_ioctl+0x65/0xc0 (?:?) __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: oss: Fix UAF at handling events with embedded SysEx data
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/6dc781778b595be94c31395b2cb167f65145d91f https://git.kernel.org/stable/c/7aad70cabd8f34cf11a9593fcd3f2ac3f5496943 https://git.kernel.org/stable/c/7c349b4f2a603202fb8c363bd2774a22ac2fddf3

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-08-15T05:59:03.147Z

Updated: 2026-08-17T05:46:37.644Z

Reserved: 2026-08-15T05:44:03.891Z

Link: CVE-2026-74388

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-08-15T06:22:40.733

Modified: 2026-08-17T06:19:33.820

Link: CVE-2026-74388

Redhat

Severity : Moderate

Publid Date: 2026-08-15T00:00:00Z

Links: CVE-2026-74388 - Bugzilla

OpenCVE Enrichment

Updated: 2026-08-21T23:45:03Z

Weaknesses

CWE-416
Use After Free
CWE-825
Expired Pointer Dereference

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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