CVE-2026-99055 tcp: reject net_iov in zerocopy receive mapping hints
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-99055?
CVE-2026-99055 is a vulnerability in Linux, published on 23 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
tcp: reject net_iov in zerocopy receive mapping hints
After copying a readable prefix, receive_fallback_to_copy() asks tcp_zerocopy_set_hint_for_skb() where page mapping can resume. If the next skb is unreadable, find_next_mappable_frag() passes its net_iov fragment to can_map_frag().
skb_frag_page() returns NULL for a net_iov, but can_map_frag() dereferences it in PageCompound(). A v7.2 KASAN run on a connected TCP socket with 64 readable bytes followed by a 4096-byte NET_IOV_DMABUF fragment reported:
BUG: KASAN: null-ptr-deref in can_map_frag tcp_zerocopy_receive -> can_map_frag Kernel panic - not syncing: KASAN: panic_on_warn set
The diagnostic inserted the net_iov directly because the test host has no devmem-capable NIC. Hardware end-to-end reachability remains untested and requires CONFIG_NET_DEVMEM plus a supported DMA-buf-bound RX queue.
Reject all net_iov fragments before skb_frag_page(). This covers both DMABUF and IOURING net_iov types while leaving page-backed checks unchanged. With the guard, the same queue copied the readable prefix, returned a 4096-byte skip hint, and completed without a fault.
Which versions are affected by CVE-2026-99055?
How do I fix CVE-2026-99055?
Upgrade to a fixed version.
Is CVE-2026-99055 being exploited?
There is no known exploitation of CVE-2026-99055 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-99055, DEBIAN-CVE-2026-99055, GHSA-7h6j-x293-w79r, UBUNTU-CVE-2026-99055.