Linux Kernel EUVD-2026-32891

In the Linux kernel, the following vulnerability has been resolved:

net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo

rtnl_fill_vfinfo() declares struct ifla_vf_broadcast on the stack without initialisation:

struct ifla_vf_broadcast vf_broadcast;

The struct contains a single fixed 32-byte field:

/* include/uapi/linux/if_link.h */ struct ifla_vf_broadcast { __u8 broadcast[32]; };

The function then copies dev->broadcast into it using dev->addr_len as the length:

memcpy(vf_broadcast.broadcast, dev->broadcast, dev->addr_len);

On Ethernet devices (the overwhelming majority of SR-IOV NICs) dev->addr_len is 6, so only the first 6 bytes of broadcast[] are written. The remaining 26 bytes retain whatever was previously on the kernel stack. The full struct is then handed to userspace via:

nla_put(skb, IFLA_VF_BROADCAST, sizeof(vf_broadcast), &vf_broadcast)

leaking up to 26 bytes of uninitialised kernel stack per VF per RTM_GETLINK request, repeatable.

The other vf_* structs in the same function are explicitly zeroed for exactly this reason - see the memset() calls for ivi, vf_vlan_info, node_guid and port_guid a few lines above. vf_broadcast was simply missed when it was added.

Reachability: any unprivileged local process can open AF_NETLINK / NETLINK_ROUTE without capabilities and send RTM_GETLINK with an IFLA_EXT_MASK attribute carrying RTEXT_FILTER_VF. The kernel walks each VF and emits IFLA_VF_BROADCAST, leaking 26 bytes of stack per VF per request. Stack residue at this call site can include return addresses and transient sensitive data; KASAN with stack instrumentation, or KMSAN, will flag the nla_put() when reproduced.

Zero the on-stack struct before the partial memcpy, matching the existing pattern used for the other vf_* structs in the same function.