Bug 2521456 (CVE-2026-74709)

Summary: CVE-2026-74709 kernel: xsk: clear metadata pointer when no timestamp is requested
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's xsk (AF_XDP sockets) component. A local attacker, by manipulating metadata flags after request processing, could cause the kernel to write a timestamp into the metadata area even when not explicitly requested. This could lead to unintended data modification within the metadata.
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Description OSIDB Bzimport 2026-08-22 15:46:31 UTC 
In the Linux kernel, the following vulnerability has been resolved:

xsk: clear metadata pointer when no timestamp is requested

User space can change metadata flags after request processing. Rereading
them during completion can therefore make the kernel write a timestamp
that was not requested when the packet was submitted.

Clear the metadata pointer during request processing unless timestamp
completion is requested. Completion handling can then use the pointer
itself instead of rereading the flags.

On the mlx5 multi-packet WQE path metadata is evaluated per batch:
xsk_tx_metadata_request() runs only for the descriptor that starts a
session, just like the checksum offload that is applied once through the
shared WQE. Only that descriptor's pointer is reset, so completion
handling can record a timestamp for the other descriptors of the session
regardless of their own XDP_TXMD_FLAGS_TIMESTAMP bit. The write stays
inside the metadata area; the single-WQE, other zero-copy, and generic
paths reset the pointer per descriptor and are unaffected.
Comment 1 Keith Grant 2026-08-24 17:45:30 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082237-CVE-2026-74709-bbb2@gregkh/T