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[86.49.249.77]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d7f653c61sm158290795e9.10.2026.01.08.08.37.52 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 08 Jan 2026 08:37:52 -0800 (PST) From: Michal Slabihoudek Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: netfilter@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.300.41.1.7\)) Subject: [BUG] connlimit breaks localhost connections since 6.17.13 Message-Id: <6989BD9F-8C24-4397-9AD7-4613B28BF0DB@gooddata.com> Date: Thu, 8 Jan 2026 17:37:41 +0100 Cc: Jaroslav Pulchart , Tomas Klouda To: netfilter@vger.kernel.org X-Mailer: Apple Mail (2.3864.300.41.1.7) Hello netfilter maintainers,=20 I would like to report a regression related to the connlimit match. Kernel versions: =E2=80=A2 6.17.12: working =E2=80=A2 6.17.13: broken =E2=80=A2 6.18.3: still broken Distribution: =E2=80=A2 CentOS Stream 9 Netfilter component: =E2=80=A2 connlimit (iptables) Description: Applying an iptables rule using the connlimit module causes TCP = connections to be dropped (client observes connection timeout), even though the rule action is LOG and not DROP/REJECT. This happens specifically when connecting from localhost to a = non-localhost IP address (i.e. not in 127.0.0.0/8). The first connection succeeds, but subsequent connections immediately time out. Removing the iptables rule with the connlimit match fully resolves the = issue. Expected behavior: =E2=80=A2 connlimit should only match and log packets =E2=80=A2 connection handling should remain unaffected when using -j LOG Actual behavior: =E2=80=A2 connections are silently dropped =E2=80=A2 client experiences TCP connection timeout Reproducer: Target port: TCP 443 iptables rule used (for custom logging only): ``` iptables -I INPUT -p tcp --dport 443 \ --tcp-flags FIN,SYN,RST,ACK SYN \ -m connlimit --connlimit-above 500 \ --connlimit-mask 32 --connlimit-saddr \ -j LOG --log-prefix "IPT-443: " ``` iptables ruleset: ``` Chain INPUT (policy ACCEPT) num pkts bytes target prot opt in out source destination 1 0 0 LOG tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 flags:0x17/0x02 #conn src/32 > 500 LOG flags 0 level 4 prefix "IPT-443: " ``` Test case: First connection from localhost to instance IP (X.X.X.X): ``` curl -I -L -k -m 3 https://X.X.X.X -> HTTP/2 200 OK ``` Immediate second connection: ``` curl -I -L -k -m 3 https://X.X.X.X -> curl: (28) Connection timed out after 3001 milliseconds ``` Without the iptables rule applied, repeated connections succeed without any issue. Notes: =E2=80=A2 This looks like a regression introduced in 6.17.13 =E2=80=A2 The behavior resembles an implicit drop, despite using LOG = only =E2=80=A2 Regression might be introduced by = https://github.com/torvalds/linux/commit/69894e5b4c5e28cda5f32af33d4a92b7a= 4b93b0e Please let me know if further debugging data (conntrack state, = traces,or kernel logs) would be helpful. Best regards.