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CVE-2026-68118
tcp: challenge ACK for non-exact RST in SYN-RECEIVED
Published 2026-08-10 (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-2026-68118 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. 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-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The SYN-RECEIVED request-socket path in tcp_check_req() accepts an in-window RST without requiring SEG.SEQ to exactly match RCV.NXT. A non-exact RST therefore removes the request instead of eliciting a challenge ACK. RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in SYN-RECEIVED: an exact RST resets the connection, while a non-exact in-window RST must trigger a challenge ACK and be dropped. Apply that check before the ACK-field validation, following the RFC sequence-number, RST, then ACK processing order. Factor the per-netns challenge ACK quota out of tcp_send_challenge_ack() so request sockets can share it. Use the request socket's send_ack() callback and its own out-of-window ACK timestamp to send and rate-limit the response.
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/tcp_input.c
net/ipv4/tcp_minisocks.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
- 2026-08-10 (2 months ago)source
- CVSS
- 8.2 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.39%, higher than 31.7% 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 |
|---|---|---|
| 3.6 | 6.6.153 | 8b0a3a094f4c |
| 3.6 | 6.12.105 | 0fe4636665d1 |
| 3.6 | 6.18.42 | 234f9ffbd9b2 |
| 3.6 | 7.1.6 | 22cec809b048 |
| 3.6 | 7.2 | a28c4fcbf774 |
| 3.0.58 | 0 | 0 |
| 3.2.37 | 0 | 0 |
| 3.4.25 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- The bug is in tcp_check_req() on the core TCP receive path (ip_rcv/tcp_v4_rcv or tcp_v6_rcv → __inet_lookup_skb on TCP_NEW_SYN_RECV → tcp_check_req); any remote host that can deliver TCP segments to an internet-facing listener reaches it with no local access.
- AC:LAttack complexity, low
- An attacker controls the forged RST (source/dest ports, SEQ sweep across the SYN-RECEIVED window up to tcp_synack_window/65535) and can retry on every handshake; no race, rare config, or victim-only state outside attacker influence is required beyond routine IP spoofing or on-path delivery.
- PR:NPrivileges required, none
- Processing occurs on the pre-authentication TCP handshake path for embryonic request sockets; no credentials, capabilities, or local account are needed—only the ability to send (or spoof) TCP packets to the target listener.
- UI:NUser interaction, none
- Handshake teardown is triggered automatically when the kernel receives the crafted RST during SYN-RECEIVED; no victim must open files, click links, or perform any other action.
- S:UScope, unchanged
- Impact is confined to incorrect TCP connection-state handling within the same host kernel; it does not cross VM, container, or IOMMU security boundaries.
- C:NConfidentiality impact, none
- This is a protocol state-machine logic flaw with no memory corruption, out-of-bounds access, use-after-free, or information disclosure—only embryonic request-socket teardown occurs.
- I:LIntegrity impact, low
- A non-exact in-window RST causes unauthorized modification of TCP connection state by dropping the embryonic request socket (embryonic_reset/inet_csk_reqsk_queue_drop) instead of preserving it per RFC 5961/RFC 9293.
- A:HAvailability impact, high
- Repeated spoofed in-window RSTs during SYN-RECEIVED can prevent TCP handshakes from completing on arbitrary listening services (HTTPS, SSH, databases, load balancers), causing sustained denial of service without kernel crash.