Bug 2528693 (CVE-2026-80838)

Summary: CVE-2026-80838 kernel: vxlan: keep the last remote linked during FDB flush
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Virtual Extensible LAN (VXLAN) component. During certain network operations, specifically a filtered bulk flush, the system can incorrectly handle remote entries. This can lead to a memory corruption vulnerability where a read-copy update (RCU) reader attempts to access an invalid memory location. An attacker could potentially exploit this to cause a denial of service, making the system unavailable.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-04 16:24:17 UTC 
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.
Comment 1 gkamathe 2026-09-08 12:44:42 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-80838.mbox