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CVE-2026-74268
tcp: clear sock_ops cb flags before force-closing a child socket
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74268 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-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A child socket inherits the listener's bpf_sock_ops_cb_flags via sk_clone_lock(). If its setup fails in tcp_v4_syn_recv_sock() / tcp_v6_syn_recv_sock(), the child is freed through put_and_exit, where inet_csk_prepare_forced_close() drops the socket lock and tcp_done() runs without it. If BPF_SOCK_OPS_STATE_CB_FLAG was inherited, tcp_done() -> tcp_set_state() calls tcp_call_bpf(), which expects the lock and trips sock_owned_by_me(): WARNING: include/net/sock.h:1799 at tcp_set_state+0x433/0x550 RIP: 0010:tcp_set_state+0x433/0x550 include/net/sock.h:1799 Call Trace: <IRQ> tcp_done+0xba/0x250 net/ipv4/tcp.c:5095 tcp_v4_syn_recv_sock+0x850/0xa50 net/ipv4/tcp_ipv4.c:1787 tcp_check_req+0xf30/0x1360 net/ipv4/tcp_minisocks.c:926 tcp_v4_rcv+0x1047/0x1b50 net/ipv4/tcp_ipv4.c:2164 </IRQ> The child is freed before it is ever established, so it should run no sock_ops callback. Clear its cb flags in inet_csk_prepare_for_destroy_sock(), the common point for the IPv4, IPv6 and chtls forced-close paths and for the MPTCP ->syn_recv_sock() failure path (dispose_child), which reaches tcp_done() on a child that was never established too.
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.
include/net/tcp.h
net/ipv4/inet_connection_sock.c
- What this is
- NETWORKING [TCP]MAINTAINERS section matched on include/net/tcp.h · 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, sid, bookworm · linux-6.12y
- 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
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.71%, higher than 52.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.16 | 5.10.270 | 5d5389b2c37c |
| 4.16 | 5.15.221 | 9f30ba9aa027 |
| 4.16 | 6.1.188 | 71e9c53220ab |
| 4.16 | 6.6.157 | 9fffa6465851 |
| 4.16 | 6.12.110 | fe23d56e9266 |
| 4.16 | 6.18.40 | ce311bd2e365 |
| 4.16 | 7.1.5 | 8874dafc9099 |
| 4.16 | 7.2 | 990348e5bb45 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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:NAttack vector, network
- Remote attackers reach inet_csk_prepare_for_forced_close() via the standard TCP input path (tcp_v4_rcv/tcp_v6_rcv → tcp_check_req → tcp_v4/v6_syn_recv_sock put_and_exit) while processing attacker-sent handshake packets in softirq, with no local access required.
- AC:LAttack complexity, low
- Attackers control handshake completion and can repeatedly force child setup failures—e.g., MPTCP JOIN/sport-mismatch dispose_child paths, ENOMEM under connection pressure in __inet_inherit_port or MD5/AO copy, or chtls setup failure—making put_and_exit reachable without conditions outside their influence.
- PR:NPrivileges required, none
- The receive path is pre-authentication TCP/MPTCP processing; no victim credentials or capabilities are required. Exploitation only needs network reachability to a listener whose admin already attached cgroup BPF sock_ops setting BPF_SOCK_OPS_STATE_CB_FLAG (common on Kubernetes/Cilium/cloud nodes).
- UI:NUser interaction, none
- No victim interaction is needed beyond normal exposure of a TCP listener; the attacker triggers the bug entirely by sending network packets that complete then fail child socket creation.
- S:UScope, unchanged
- Vulnerability impact stays within the kernel on the host receiving the traffic; it does not cross VM, container runtime, or IOMMU security boundaries and represents standard in-kernel memory/lock safety impact.
- C:HConfidentiality impact, high
- Inherited BPF_SOCK_OPS_STATE_CB_FLAG causes tcp_call_bpf() to run on an unlocked, partially torn-down child socket; BPF helpers can read tcp_sock fields without proper locking, enabling unsynchronized kernel memory reads that could disclose sensitive data.
- I:HIntegrity impact, high
- tcp_call_bpf() marks is_locked_tcp_sock while the socket lock was dropped, allowing cgroup BPF sock_ops programs to call bpf_setsockopt and modify tcp_sock/kernel state during forced close, creating plausible memory corruption and control-flow compromise primitives.
- A:HAvailability impact, high
- sock_owned_by_me() WARN fires on this path and concurrent BPF access during tcp_done()/inet_csk_destroy_sock() can cause kernel oops or panic; remote attackers can repeatedly trigger the softirq failure path for denial of service on internet-facing BPF-enabled servers.