Look up another CVE · open CVE-2026-90051 in the interactive tracker
CVE-2026-90051
tcp: reject non zerocopy devmem tx
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem net/ipv4. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-90051 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Devmem tcp tx doesn't work without zero-copy, however it's not currently enforced if NETIF_F_SG isn't present. In this case, tcp_sendmsg_locked() will try the copy path and try to copy data from an iovec which consists of offsets into the dma-buf and would normally fail. Moreover, d9c56501c72fd ("net: tcp: block mixing readable and unreadable frags") relies on that and assumes that the devmem binding is present IFF we're using the zero-copy path, which can be used to mix net-iov and pages in a single skb, and break invariants. Let's reject devmem tx without zero-copy. Note, the parameter check the patch is modifying is too loose, we can create an io_uring request with dmabuf_id and all ZC flags, but which won't have the binding. We replace it with stricter validation.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/ipv4/tcp.c
- What this is
- NETWORKING [TCP]MAINTAINERS section matched on net/ipv4/tcp*.c · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_INET /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_INET
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-17 (31 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 4.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/ipv4
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.52 | 2151b2bcf6fc |
| 6.16 | 7.2.6 | b04326c7927a |
| 6.16 | 7.3 | 125755776bc6 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The triggering input is local sendmsg or io_uring IORING_OP_SENDMSG_ZC into tcp_sendmsg_locked(): SO_ZEROCOPY, MSG_ZEROCOPY, and an SCM_DEVMEM_DMABUF cmsg that sets sockc.dmabuf_id. A remote TCP peer never supplies that cmsg or those send flags; it only receives the resulting segments.
- AC:LAttack complexity, low
- The attacker drives both sendmsg calls: a MSG_ZEROCOPY+SCM_DEVMEM_DMABUF send queues net-iov (unreadable) frags, then a later sendmsg with sockc.dmabuf_id while zc==0 (sk_route_caps lacks NETIF_F_SG, so the copy path runs with binding set) appends pages onto that skb. MSG_MORE retains the write-queue tail; no victim race is required.
- PR:LPrivileges required, low
- NETDEV_CMD_BIND_TX has no GENL_ADMIN_PERM, and SO_ZEROCOPY plus __sock_cmsg_send(SCM_DEVMEM_DMABUF) have no capability checks. An unprivileged user can bind a TX dmabuf and reach the zc/binding check in tcp_sendmsg_locked; any extra CAP_NET_ADMIN is only the user-namespace kind.
- UI:NUser interaction, none
- The attacker enables SO_ZEROCOPY, binds a dmabuf via netdev-genl NETDEV_CMD_BIND_TX, and issues the crafted sendmsg/IORING_OP_SENDMSG_ZC sequence on their own TCP socket; no victim mount, open, or other interactive action is required.
- S:UScope, unchanged
- Mixing net_iov and page frags corrupts skb/TX processing on the sending host inside tcp_sendmsg_locked and later frag walkers. It does not cross a VM/guest or IOMMU authority; __skb_frag_dma_map still classifies each frag with skb_frag_is_net_iov.
- C:HConfidentiality impact, high
- A mixed skb keeps skb->unreadable from skb_add_rx_frag_netmem while the zc==0 path adds page frags via skb_fill_page_desc. Walkers such as tcp_md5_hash_skb_data use skb_frag_foreach_page/skb_frag_page() on net_iovs (NULL) and kmap that pointer, enabling kernel memory disclosure.
- I:HIntegrity impact, high
- Appending sk_page_frag pages onto a net-iov skb via the zc==0 copy path in tcp_sendmsg_locked is frag-type confusion: TX, refcount, and skb_fill_page_desc versus skb_add_rx_frag_netmem cannot treat mixed backing consistently, which yields corrupted skb metadata and write or control-flow primitives.
- A:HAvailability impact, high
- Mixed readable/unreadable frags blow up down the stack: skb_copy_bits/skb_checksum hit WARN_ON_ONCE(!skb_frags_readable), splice hits WARN_ON_ONCE(!skb_frag_page), and kmap of a NULL net_iov page oopses or panics the kernel.