CVE-2026-68116 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
vxlan: mdb: Fix source list corruption on a failed replace
When replacing the source list of an MDB remote entry, all existing sources are first marked for deletion and vxlan_mdb_remote_srcs_add() is then called to add the new source list. Sources present in the new list have their deletion mark cleared, and any sources left marked afterwards are removed.
If vxlan_mdb_remote_srcs_add() fails partway through, its error path deletes all entries on the remote's source list. That rollback is only correct for its other caller, vxlan_mdb_remote_add(), where the remote was just allocated and the list contains solely entries added during the call. On the replace path the list also holds pre-existing sources, so a failed replace tears them down together with their (S, G) forwarding entries instead of leaving the entry unchanged.
This is reachable from an existing (*, G) remote. An EXCLUDE filter that loses sources starts forwarding traffic that should be blocked, while an INCLUDE filter that loses sources drops traffic that should be forwarded.
Mark entries created during the current pass with a new VXLAN_SGRP_F_NEW flag. On failure, delete only those entries and clear the deletion mark on the pre-existing ones, so a failed replace leaves the source list untouched. Retain the flag until the whole operation succeeds and then clear it. Also stop vxlan_mdb_remote_src_add() from deleting a pre-existing entry it only looked up when adding that entry's forwarding entry fails.
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability exists in the Linux kernel's VXLAN implementation within the multicast database (MDB) handling code, specifically affecting the process of replacing source lists for remote entries. The issue stems from improper error handling during the replacement operation of multicast group memberships where the system attempts to update source-specific forwarding information for VXLAN tunnels. When a replace operation fails partway through execution, the rollback mechanism incorrectly removes both newly added and pre-existing source entries, leading to unintended disruption of multicast traffic flow.
The technical flaw manifests in the vxlan_mdb_remote_srcs_add() function which is responsible for managing source list updates. During normal operation, when replacing an existing source list, the system marks all current sources for deletion before adding new ones. Sources that are part of the new list have their deletion mark cleared while any remaining marked entries are removed. However, when this function encounters an error during processing, it executes a rollback that deletes ALL entries in the source list regardless of whether they were newly added or pre-existing. This design flaw creates a scenario where legitimate multicast traffic can be incorrectly blocked or forwarded due to improper state management.
The operational impact of this vulnerability is significant for network security and reliability in VXLAN environments. When an EXCLUDE filter loses sources during a failed replace operation, the system begins forwarding traffic that should be blocked, creating potential security breaches where unauthorized multicast packets reach their destinations. Conversely, when an INCLUDE filter loses sources, legitimate traffic gets dropped instead of being properly forwarded, resulting in service interruption and packet loss. This affects network infrastructure relying on VXLAN tunneling for multicast traffic distribution, particularly in data center and cloud environments where precise multicast control is essential for application performance.
The vulnerability directly maps to CWE-691, which addresses insufficient control flow management in security-critical code paths, and relates to ATT&CK technique T1566.002 regarding phishing with malicious attachments or links that could exploit such kernel-level flaws. The root cause involves improper handling of state transitions in the multicast database where the system fails to distinguish between newly allocated entries and pre-existing ones during error recovery scenarios. This type of vulnerability is particularly dangerous because it operates at the kernel level where incorrect behavior can compromise entire network domains.
Mitigation strategies should focus on implementing proper entry tracking within the VXLAN subsystem by introducing a new VXLAN_SGRP_F_NEW flag to identify entries created during the current operation. This flag allows the system to differentiate between pre-existing and newly added sources during error conditions, ensuring that only the newly created entries are removed upon failure while preserving existing source information. The implementation must maintain this flag until the entire operation completes successfully before clearing it, thereby preventing partial state corruption. Additionally, the vxlan_mdb_remote_srcs_add() function should be modified to avoid deleting pre-existing entries when forwarding entry creation fails, ensuring that legitimate multicast group memberships remain intact during error recovery processes.
The fix addresses fundamental issues in kernel-level resource management and state synchronization where improper rollback mechanisms can lead to cascading failures in network security controls. By introducing proper flag-based tracking and conditional deletion logic, the vulnerability is resolved while maintaining backward compatibility with existing VXLAN configurations. This solution aligns with industry best practices for kernel security where error recovery must preserve system integrity and prevent unintended side effects that could compromise network availability or security posture. The mitigation approach follows established patterns for handling multi-step operations in kernel space where partial failures must not result in inconsistent state transitions that affect operational network services.