{"id":"CVE-2023-53635","state":"PUBLISHED","title":"netfilter: conntrack: fix wrong ct->timeout value","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: conntrack: fix wrong ct->timeout value\n\n(struct nf_conn)->timeout is an interval before the conntrack\nconfirmed.  After confirmed, it becomes a timestamp.\n\nIt is observed that timeout of an unconfirmed conntrack:\n- Set by calling ctnetlink_change_timeout(). As a result,\n  `nfct_time_stamp` was wrongly added to `ct->timeout` twice.\n- Get by calling ctnetlink_dump_timeout(). As a result,\n  `nfct_time_stamp` was wrongly subtracted.\n\nCall Trace:\n <TASK>\n dump_stack_lvl\n ctnetlink_dump_timeout\n __ctnetlink_glue_build\n ctnetlink_glue_build\n __nfqnl_enqueue_packet\n nf_queue\n nf_hook_slow\n ip_mc_output\n ? __pfx_ip_finish_output\n ip_send_skb\n ? __pfx_dst_output\n udp_send_skb\n udp_sendmsg\n ? __pfx_ip_generic_getfrag\n sock_sendmsg\n\nSeparate the 2 cases in:\n- Setting `ct->timeout` in __nf_ct_set_timeout().\n- Getting `ct->timeout` in ctnetlink_dump_timeout().\n\nPablo appends:\n\nUpdate ctnetlink to set up the timeout _after_ the IPS_CONFIRMED flag is\nset on, otherwise conntrack creation via ctnetlink breaks.\n\nNote that the problem described in this patch occurs since the\nintroduction of the nfnetlink_queue conntrack support, select a\nsufficiently old Fixes: tag for -stable kernel to pick up this fix.","publishedAt":"2025-10-07T15:19:36.973Z","updatedAt":"2026-10-15T21:41:32.395Z","severity":{"score":8.2,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"80c5ba0078e20d926d11d0778f9a43902664ebf0","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"f612ae1ab4793701caf39386fb3b7f4b3ef44e48","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"73db1b8f2bb6725b7391e85aab41fdf592b3c0c1","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/netfilter/nf_conntrack_core.h","net/netfilter/nf_conntrack_netlink.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.4","versionType":"semver"},{"version":"6.1.28","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.2.15","status":"unaffected","lessThanOrEqual":"6.2.*","versionType":"semver"},{"version":"6.3.2","status":"unaffected","lessThanOrEqual":"6.3.*","versionType":"semver"},{"version":"6.4","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/netfilter/nf_conntrack_core.h","net/netfilter/nf_conntrack_netlink.c"]}],"references":["https://git.kernel.org/stable/c/80c5ba0078e20d926d11d0778f9a43902664ebf0","https://git.kernel.org/stable/c/ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8","https://git.kernel.org/stable/c/f612ae1ab4793701caf39386fb3b7f4b3ef44e48","https://git.kernel.org/stable/c/73db1b8f2bb6725b7391e85aab41fdf592b3c0c1"],"weaknesses":[],"ingestedAt":"2026-10-29T20:06:33.064Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2023/53xxx/CVE-2023-53635.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2023-53635","state":"PUBLISHED","datePublished":"2025-10-07T15:19:36.973Z","dateUpdated":"2026-10-15T21:41:32.395Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-10-07T15:16:59.657Z"},"containers":{"cna":{"title":"netfilter: conntrack: fix wrong ct->timeout value","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: conntrack: fix wrong ct->timeout value\n\n(struct nf_conn)->timeout is an interval before the conntrack\nconfirmed.  After confirmed, it becomes a timestamp.\n\nIt is observed that timeout of an unconfirmed conntrack:\n- Set by calling ctnetlink_change_timeout(). As a result,\n  `nfct_time_stamp` was wrongly added to `ct->timeout` twice.\n- Get by calling ctnetlink_dump_timeout(). As a result,\n  `nfct_time_stamp` was wrongly subtracted.\n\nCall Trace:\n <TASK>\n dump_stack_lvl\n ctnetlink_dump_timeout\n __ctnetlink_glue_build\n ctnetlink_glue_build\n __nfqnl_enqueue_packet\n nf_queue\n nf_hook_slow\n ip_mc_output\n ? __pfx_ip_finish_output\n ip_send_skb\n ? __pfx_dst_output\n udp_send_skb\n udp_sendmsg\n ? __pfx_ip_generic_getfrag\n sock_sendmsg\n\nSeparate the 2 cases in:\n- Setting `ct->timeout` in __nf_ct_set_timeout().\n- Getting `ct->timeout` in ctnetlink_dump_timeout().\n\nPablo appends:\n\nUpdate ctnetlink to set up the timeout _after_ the IPS_CONFIRMED flag is\nset on, otherwise conntrack creation via ctnetlink breaks.\n\nNote that the problem described in this patch occurs since the\nintroduction of the nfnetlink_queue conntrack support, select a\nsufficiently old Fixes: tag for -stable kernel to pick up this fix."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"80c5ba0078e20d926d11d0778f9a43902664ebf0","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"f612ae1ab4793701caf39386fb3b7f4b3ef44e48","versionType":"git"},{"version":"a4b4766c3cebb4018167e06b863d8e95b7274757","status":"affected","lessThan":"73db1b8f2bb6725b7391e85aab41fdf592b3c0c1","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/netfilter/nf_conntrack_core.h","net/netfilter/nf_conntrack_netlink.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.4","versionType":"semver"},{"version":"6.1.28","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.2.15","status":"unaffected","lessThanOrEqual":"6.2.*","versionType":"semver"},{"version":"6.3.2","status":"unaffected","lessThanOrEqual":"6.3.*","versionType":"semver"},{"version":"6.4","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/netfilter/nf_conntrack_core.h","net/netfilter/nf_conntrack_netlink.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/80c5ba0078e20d926d11d0778f9a43902664ebf0"},{"url":"https://git.kernel.org/stable/c/ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8"},{"url":"https://git.kernel.org/stable/c/f612ae1ab4793701caf39386fb3b7f4b3ef44e48"},{"url":"https://git.kernel.org/stable/c/73db1b8f2bb6725b7391e85aab41fdf592b3c0c1"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","baseScore":8.2,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - The corruption occurs in the conntrack packet path — every new flow traversing an NFQUEUE-with-conntrack ruleset (IPS/firewall daemons) or a tc/XDP conntrack BPF program gets its `ct->timeout` mangled during `nf_hook_slow`/`nf_confirm` processing of received packets. A remote peer sending traffic to such a host drives the enqueue/verdict/confirm cycle and controls the rate at which broken entries accumulate.\nAC:L - The double-add of `nfct_time_stamp` is deterministic for every unconfirmed conntrack whose timeout is set, with no race, memory-layout, or timing dependency; the attacker simply generates new flows. Scoring the vulnerable (queue/BPF conntrack-enabled) deployment, no condition lies outside the attacker's control.\nPR:N - On a host running a conntrack-aware NFQUEUE daemon or BPF conntrack program, unauthenticated remote packets are sufficient to create the mis-timed entries — no credentials on the target are needed. Even in the purely local framing, the nfnetlink gate is `netlink_net_capable(CAP_NET_ADMIN)`, which is namespace-scoped and reachable by an unprivileged user via `unshare -Urn`.\nUI:N - Exploitation is entirely driven by network traffic and the kernel's own enqueue/verdict/confirm cycle; no victim action of any kind is required.\nS:U - The corrupted state (`ct->timeout`) and its effects stay within the kernel networking subsystem's own security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:N - No kernel memory is read out of bounds and no sensitive data is exposed; the only wrong value returned is a bogus timeout in `ctnetlink_dump_timeout()`, delivered to an already-privileged queue daemon and derived from `jiffies`, which is not sensitive.\nI:L - The bug writes an incorrect lifetime into kernel-managed connection-tracking state, so tracked flows either persist far past their policy-mandated expiry (keeping stateful `ESTABLISHED` acceptance and NAT bindings alive) or vanish immediately, altering the firewall policy the kernel enforces. The modification is limited and its resulting value is not attacker-chosen.\nA:H - Entries that never age out fill the conntrack table, after which the host drops all new connections (`nf_conntrack: table full`) and the condition persists for days rather than the configured 30–120 s; in the opposite regime every new entry is expired at confirmation, breaking stateful filtering and NAT for all traffic. Either outcome is a complete loss of the host's networking availability."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T09:15:15.798Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.1.28"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.2.15"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.3.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.4"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2023-53635","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-15T21:36:08.236702Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-15T21:41:32.395Z"}}]}}}