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CVE-2026-68284
bpf, sockmap: Fix cork use-after-free in tcp_bpf_sendmsg()
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem net/ipv4. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-68284 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
tcp_bpf_sendmsg() keeps msg_tx across sk_stream_wait_memory(), which drops and reacquires the socket lock. Its error path tries to decide whether msg_tx names the local temporary message by comparing it with the current value of psock->cork. This comparison is unsafe when two threads send on the same socket: Thread A Thread B msg_tx = psock->cork sk_msg_alloc() fails sk_stream_wait_memory() releases the socket lock acquires the socket lock completes the cork psock->cork = NULL frees the cork reacquires the socket lock msg_tx != psock->cork sk_msg_free(msg_tx) The stale cork is therefore mistaken for the local temporary message and freed again. KASAN reported: BUG: KASAN: slab-use-after-free in sk_msg_free+0x49/0x50 Read of size 4 at addr ffff88810c908800 by task poc/90 Call Trace: sk_msg_free+0x49/0x50 tcp_bpf_sendmsg+0x14f5/0x1cc0 __sys_sendto+0x32c/0x3a0 __x64_sys_sendto+0xdb/0x1b0 Allocated by task 89: __kasan_kmalloc+0x8f/0xa0 tcp_bpf_sendmsg+0x16b3/0x1cc0 Freed by task 91: __kasan_slab_free+0x43/0x70 kfree+0x131/0x3c0 tcp_bpf_sendmsg+0xec3/0x1cc0 msg_tx can only name the stack-local tmp or the shared cork. Check for tmp directly so a changed psock->cork cannot turn a shared message into an apparent local one.
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_bpf.c
- What this is
- BPF [L7 FRAMEWORK] (sockmap)MAINTAINERS section matched on net/ipv4/tcp_bpf.c · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_INET|CONFIG_NET_SOCK_MSG' /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, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_INET, CONFIG_NET_SOCK_MSG
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-08-10 (2 months 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
- 0.14%, higher than 2.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 4.20 | 5.10.265 | 0688e6fe599d |
| 4.20 | 5.15.216 | b2bcbeabfd84 |
| 4.20 | 6.1.183 | 54be47e7cbb9 |
| 4.20 | 6.6.148 | ee762f684eef |
| 4.20 | 6.12.101 | cde4d6bcd9b7 |
| 4.20 | 6.18.42 | 786d690257ec |
| 4.20 | 7.1.6 | 752b1159ed5d |
| 4.20 | 7.2 | 2d66a033864e |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
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 vulnerability is triggered by local `sendmsg()`/`sendto()` syscalls issued concurrently by two threads on the same TCP socket attached to a BPF sockmap; the remote peer cannot drive the race, so this is a local attack surface.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: it owns both sending threads, can force the `wait_for_memory` path deterministically with a small SO_SNDBUF plus a large blocking send, and can force `sk_stream_wait_memory()` to fail via SO_SNDTIMEO or a socket error, making the stale-cork free reliably reachable.
- PR:LPrivileges required, low
- Once the sockmap and sk_msg verdict/cork program are installed by the platform (a standard deployment such as Cilium/Istio sockops acceleration), an ordinary unprivileged local process owning a socket in the map triggers the bug with plain send syscalls; no capability check guards `tcp_bpf_sendmsg()` itself.
- UI:NUser interaction, none
- The attacker's own two threads perform all the required sends; no action by any other user or victim process is needed.
- S:UScope, unchanged
- The use-after-free corrupts kernel slab and page state within the same kernel security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- `sk_msg_free()` reads the freed `sk_msg` cork object (KASAN slab-use-after-free read), and by reclaiming that slab object with attacker-groomed data the freed scatterlist can be steered to leak or expose arbitrary kernel memory contents.
- I:HIntegrity impact, high
- Beyond the stale read, the path re-frees the cork's scatterlist pages and uncharges socket memory, giving a double-free/page-refcount-underflow primitive on an attacker-groomable slab object, which is classically leveraged into arbitrary kernel write and control-flow hijack.
- A:HAvailability impact, high
- The use-after-free and duplicate page release corrupt slab and page allocator state, reliably producing a kernel oops or panic and taking the whole system down.