CVE-2026-63983 Details
Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: fix packet loop on netem when duplicate is on When netem duplicates a packet it re-enqueues the copy at the root qdisc. If another netem sits in the tree the copy can be duplicated again, recursing until the stack or memory is exhausted. The original duplication guard temporarily zeroed q->duplicate around the re-enqueue, but that does not cover all cases because it is per-qdisc state shared across all concurrent enqueue paths and is not safe without additional locking. Use the skb tc_depth field introduced in an earlier patch: - increment it on the duplicate before re-enqueue - skip duplication for any skb whose tc_depth is already non-zero. This marks the packet itself rather than mutating qdisc state, therefore it is safe regardless of tree topology or concurrency.
A vulnerability in the Linux kernel's network scheduling component, specifically within the netem (network emulator) module, has been addressed. This issue arose when netem duplicated a packet, re-enqueuing the copy at the root queue discipline (qdisc). If another netem instance was in the tree, the copy could be duplicated again, leading to excessive recursion that could exhaust system stack or memory resources. The initial safeguard against duplication only temporarily reset the per-qdisc duplicate state, which was not safe for concurrent enqueue operations. The vulnerability has been fixed by utilizing the skb (socket buffer) tc_depth field to track packet duplication more reliably. The tc_depth is incremented for duplicates before re-enqueuing, and any packet with a non-zero tc_depth is skipped, ensuring safe handling regardless of tree structure or concurrency.
Users can upgrade to the patched version of the Linux kernel available in the Linux kernel stable tree to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No CVSS 3.x data is available for this CVE.
No data available for CVSS Version 2.0 on this CVE.
No SSVC data is available for this CVE.
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Weakness Enumeration
No weakness enumeration is available for this CVE.
Affected Products
No affected product data is available for this CVE.
Change History
1 change record found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 19, 2026 | New CVE Received | kernel.org |