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CVE Record

CVE-2025-39997: ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free

In the Linux kernel, the following vulnerability has been resolved: ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free The previous commit 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at removal") patched a UAF issue caused by the error timer. However, because the error timer kill added in this patch occurs after the endpoint delete, a race condition to UAF still occurs, albeit rarely. Additionally, since kill-cleanup for urb is also missing, freed memory can be accessed in interrupt context related to urb, which can cause UAF. Therefore, to prevent this, error timer and urb must be killed before freeing the heap memory.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-39997 is a Linux kernel bug in the ALSA USB audio/MIDI removal path. A rare race can let kernel code touch memory after it has been freed, which can crash systems or create undefined kernel behavior. Public sources do not provide CVSS, impact scoring, or confirmed exploitation.

Executive priority

Treat as a patch-management item with uncertain severity. Prioritize fleets where USB audio/MIDI devices are used or allowed, especially workstations, labs, kiosks, and systems with physical USB access.

Technical view

The flaw is a use-after-free race in snd_usbmidi_free. The prior timer cleanup fix ran too late, after endpoint deletion, and URB cleanup was also missing. The fix requires killing the error timer and URBs before freeing related heap memory.

Likely exposure

Exposure is likely limited to Linux systems running affected kernels that use the ALSA USB audio/MIDI code path. The source bundle lists affected Linux versions including 6.16, 6.1.175, 6.16.11, 6.17.1, and 6.18, but distribution backports must be verified separately.

Exploitation context

The CVE is not listed as KEV, and the supplied sources do not claim active exploitation or provide public exploit evidence. Attack prerequisites are not fully described; the bug is tied to USB audio/MIDI device cleanup and interrupt-context URB handling.

Researcher notes

The strongest evidence is the kernel fix description: timer cleanup after endpoint deletion still left a rare UAF, and missing URB kill-cleanup allowed interrupt-context access to freed memory. No CVSS, CWE, or exploitability detail is provided.

Mitigation direction

  • Apply vendor or distribution kernel updates containing the stable fixes.
  • Prioritize systems using USB audio or MIDI peripherals.
  • Check distribution advisories because kernel backports may change version-based exposure.
  • Where feasible, limit untrusted USB audio/MIDI device use until patched.

Validation and detection

  • Inventory Linux kernel versions across exposed endpoints and servers.
  • Check whether ALSA USB audio/MIDI support is present or loaded.
  • Map installed kernels against vendor advisories and the listed stable commits.
  • Confirm patched kernels include timer and URB cleanup before memory free.
Prepared
Confidence
medium
Sources
9

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2025-39997 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
8Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux06513dd6d32c37d0364db8488cfdf3e14da238a8, efaf61052b8ff9ee8968912fbaf02c2847c78ede, 647410a7da46067953a53c0d03f8680eff570959, c611b9e55174e439dcd85a72969b43a95f3827a4, 0718a78f6a9f04b88d0dc9616cc216b31c5f3cf1, 0718a78f6a9f04b88d0dc9616cc216b31c5f3cf1, 0718a78f6a9f04b88d0dc9616cc216b31c5f3cf1, 62066758d2ae169278e5d6aea5995b1b6f6ddeb5, 6.1.167, 6.15.3unaffected
LinuxLinux6.16, 0, 6.1.175, 6.16.11, 6.17.1, 6.18affected
Weakness

CWE details

No CWE listed

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