CVE-2026-74388: ALSA: seq: oss: Fix UAF at handling events with embedded SysEx data
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 sndseqossmidiputc() called from sndseqossprocessevent()). 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 sndseqossmidicheckexitport()), 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 (snduselockt) 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 sndseqossprocessevent() 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 sndseqeventdup+0x40c/0x470 RIP: 0033:0x7f2cb66a6340 Read of size 6 Call trace: dumpstacklvl+0x73/0xb0 (?:?) printreport+0xd1/0x650 (?:?) srsoaliasreturnthunk+0x5/0xfbef5 (?:?) virtaddrvalid+0x1a7/0x340 (?:?) kasancompletemodereportinfo+0x64/0x200 (?:?) kasanreport+0xf7/0x130 (?:?) sndseqeventdup+0x40c/0x470 (?:?) kasancheckrange+0x10c/0x1c0 (?:?) asanmemcpy+0x27/0x70 (?:?) sndseqeventdup+0x9/0x470 (?:?) sndseqclientenqueueevent+0x139/0x240 (?:?) rawspinunlockirqrestore+0x4b/0x60 (?:?) sndseqkernelclientenqueue+0x102/0x120 (?:?) sndseqosswrite+0x416/0x4e0 (?:?) apparmorfilepermission+0x20/0x30 (?:?) odevwrite+0x3b/0x60 (?:?) vfswrite+0x1ce/0x850 (?:?) lockrelease+0xc8/0x2a0 (?:?) kasancheckwrite+0x18/0x20 (?:?) mutexunlockslowpath+0x129/0x510 (?:?) ksyswrite+0xe1/0x180 (?:?) mutexunlock+0x16/0x20 (?:?) odevioctl+0x65/0xc0 (?:?) x64syswrite+0x46/0x60 (?:?) x64syscall+0x7d/0x20d0 (?:?) dosyscall64+0xc1/0x360 (arch/x86/entry/syscall64.c:87) entrySYSCALL64afterhwframe+0x77/0x7f (?:?)
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.1.191 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.6.160 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.12.114 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 6.18.40 - Upgrade
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linux/Kernelto a version that resolves this vulnerability.Fixed in 7.1.5 - Upgrade
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.16~24.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38~24.04.4 - Upgrade
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ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1036.39 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1008.9 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 7.1.5-1 - Upgrade
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debian/linuxto a version that resolves this vulnerability.Fixed in 7.2.12-1Fixed in 7.2.14-1 - Compensating control
Extend the snd_use_lock_t refcount held by snd_seq_oss_process_event() until the sequencer dispatcher has processed the event, then release the refcount in the caller after dispatch; this keeps the original SysEx data.ext.ptr resources alive until snd_seq_event_dup() copies them.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-74388?
The severity of CVE-2026-74388 is rated as 55.
What type of vulnerability is identified in CVE-2026-74388?
CVE-2026-74388 is classified as a Use After Free vulnerability.
How does CVE-2026-74388 affect the Linux kernel?
CVE-2026-74388 affects the Linux kernel's ALSA sequencer by improperly handling events containing embedded SysEx data.
What is the recommended action for CVE-2026-74388?
It is recommended to update the Linux kernel to the patched version that resolves CVE-2026-74388.
When was CVE-2026-74388 published?
CVE-2026-74388 was published on August 15, 2026.