UBUNTU-CVE-2026-80838

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UBUNTU-CVE-2026-80838

Summary:

Details: In the Linux kernel, the following vulnerability has been resolved: vxlan: keep the last remote linked during FDB flush A non-nexthop FDB entry is expected to have at least one remote while it remains reachable through the FDB hash table. A filtered bulk flush violates this invariant when every remote matches: It unlinks the last remote in vxlan_fdb_dst_destroy() and only afterwards tells vxlan_flush() to destroy the parent FDB entry. An RCU reader can find the parent during this interval. first_remote_rcu() then applies list_entry_rcu() to the empty list head, producing an invalid remote pointer that the receive learning path can read from and write to. When a matching remote is the sole remaining remote, leave it linked and ask the caller to destroy the entire FDB entry. vxlan_fdb_destroy() keeps the remote attached while sending the deletion notification and removing the parent from the lookup structures.

References: https://ubuntu.com/security/CVE-2026-80838, https://www.cve.org/CVERecord?id=CVE-2026-80838, https://git.kernel.org/linus/d5d4a7b538b52db63927773a8905fcd9f78a42e2