Bug 2516843 (CVE-2026-74339)

Summary: CVE-2026-74339 kernel: ALSA: seq: Clear variable event pointer on read
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the ALSA (Advanced Linux Sound Architecture) sequencer component of the Linux kernel. A local attacker, by writing a direct variable event to itself, can read back a kernel memory address from the returned event header. This information disclosure could potentially be used to bypass Address Space Layout Randomization (ASLR) and facilitate further attacks.
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Description OSIDB Bzimport 2026-08-15 06:36:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: Clear variable event pointer on read

snd_seq_read() copies a queued variable-length event header to userspace
before expanding the payload. Queued variable-length events use
SNDRV_SEQ_EXT_CHAINED internally, and data.ext.ptr points at the first
extension cell.

The read side strips SNDRV_SEQ_EXT_* bits from data.ext.len before the
copy, but it leaves data.ext.ptr untouched. A userspace sequencer client
can therefore write a direct variable event to itself and read back the
extension-cell kernel address from the returned header.

Clear the temporary header pointer before copy_to_user(). The original
queued event remains unchanged and is still passed to
snd_seq_expand_var_event(), so payload expansion keeps using the
internal chain.
Comment 1 Keith Grant 2026-08-20 17:56:58 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081557-CVE-2026-74339-9cd8@gregkh/T