In the Linux kernel, the following vulnerability has been resolved:
ipvs: reload ip header after head reallocation
__ip_vs_get_out_rt() calls skb_ensure_writable() which may
reallocate skb->head.
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - The flaw is in ip_vs_bypass_xmit() on the IPVS netfilter receive path (NF_INET_LOCAL_IN/FORWARD); remote IPv4 packets to a configured virtual-server VIP reach ip_vs_in_hook() and ip_vs_leave() without local syscalls or ioctl.
AC:L - Once cache_bypass is enabled on a fwmark IPVS service with no backend, an attacker can repeatedly send traffic to the VIP; cloned skbs (common with bridging, mirroring, or shared receive buffers) make skb_ensure_writable() reallocate skb->head deterministically.
PR:N - Exploitation requires only sending IP packets to the load balancer VIP; IPVS/cache_bypass configuration is an operator prerequisite on the target, not a Linux capability the remote attacker must hold.
UI:N - No victim interaction is required; kernel processing of attacker-crafted network packets on the IPVS bypass transmit path alone triggers the stale header pointer use after skb head reallocation.
S:U - Impact is kernel heap corruption and load-balancer compromise within the host kernel security domain; it does not cross VM, container, or IOMMU boundaries to another security authority.
C:H - After pskb_expand_head() frees the old skb->head, ip_send_check() uses the stale iph pointer and ip_fast_csum() reads attacker-influenced bytes from freed kmalloc memory, a classic use-after-free information disclosure primitive.
I:H - ip_send_check() writes through the stale iph pointer (zeroing and updating the checksum field) into freed/reallocated slab memory, enabling heap corruption and potential arbitrary kernel write or control-flow hijack primitives.
A:H - Writing and reading through a stale IP header pointer after skb head reallocation can corrupt adjacent kernel heap objects or dereference freed memory, causing kernel oops, panic, or hang and repeatable denial of service.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - The flaw is in ip_vs_bypass_xmit() on the IPVS netfilter receive path (NF_INET_LOCAL_IN/FORWARD); remote IPv4 packets to a configured virtual-server VIP reach ip_vs_in_hook() and ip_vs_leave() without local syscalls or ioctl.
AC:L - Once cache_bypass is enabled on a fwmark IPVS service with no backend, an attacker can repeatedly send traffic to the VIP; cloned skbs (common with bridging, mirroring, or shared receive buffers) make skb_ensure_writable() reallocate skb->head deterministically.
PR:N - Exploitation requires only sending IP packets to the load balancer VIP; IPVS/cache_bypass configuration is an operator prerequisite on the target, not a Linux capability the remote attacker must hold.
UI:N - No victim interaction is required; kernel processing of attacker-crafted network packets on the IPVS bypass transmit path alone triggers the stale header pointer use after skb head reallocation.
S:U - Impact is kernel heap corruption and load-balancer compromise within the host kernel security domain; it does not cross VM, container, or IOMMU boundaries to another security authority.
C:H - After pskb_expand_head() frees the old skb->head, ip_send_check() uses the stale iph pointer and ip_fast_csum() reads attacker-influenced bytes from freed kmalloc memory, a classic use-after-free information disclosure primitive.
I:H - ip_send_check() writes through the stale iph pointer (zeroing and updating the checksum field) into freed/reallocated slab memory, enabling heap corruption and potential arbitrary kernel write or control-flow hijack primitives.
A:H - Writing and reading through a stale IP header pointer after skb head reallocation can corrupt adjacent kernel heap objects or dereference freed memory, causing kernel oops, panic, or hang and repeatable denial of service.
CVSS 3.1