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CVE Record

CVE-2023-53635: netfilter: conntrack: fix wrong ct->timeout value

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: fix wrong ct->timeout value (struct nf_conn)->timeout is an interval before the conntrack confirmed. After confirmed, it becomes a timestamp. It is observed that timeout of an unconfirmed conntrack: - Set by calling ctnetlink_change_timeout(). As a result, `nfct_time_stamp` was wrongly added to `ct->timeout` twice. - Get by calling ctnetlink_dump_timeout(). As a result, `nfct_time_stamp` was wrongly subtracted. Call Trace: <TASK> dump_stack_lvl ctnetlink_dump_timeout __ctnetlink_glue_build ctnetlink_glue_build __nfqnl_enqueue_packet nf_queue nf_hook_slow ip_mc_output ? __pfx_ip_finish_output ip_send_skb ? __pfx_dst_output udp_send_skb udp_sendmsg ? __pfx_ip_generic_getfrag sock_sendmsg Separate the 2 cases in: - Setting `ct->timeout` in __nf_ct_set_timeout(). - Getting `ct->timeout` in ctnetlink_dump_timeout(). Pablo appends: Update ctnetlink to set up the timeout _after_ the IPS_CONFIRMED flag is set on, otherwise conntrack creation via ctnetlink breaks. Note that the problem described in this patch occurs since the introduction of the nfnetlink_queue conntrack support, select a sufficiently old Fixes: tag for -stable kernel to pick up this fix.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

A Linux kernel netfilter conntrack bug can mishandle connection timeout values when conntrack entries are created or reported through ctnetlink. The sources show a kernel logic fix, but do not provide CVSS, impact category, or exploitation evidence.

Executive priority

Treat this as a kernel maintenance item until severity is clarified. Prioritize patch tracking for firewalls, routers, security appliances, Kubernetes nodes, and Linux systems relying on netfilter connection tracking.

Technical view

nf_conn->timeout is an interval before confirmation and a timestamp after confirmation. The bug added or subtracted nfct_time_stamp incorrectly for unconfirmed conntrack entries; stable patches separate set and dump behavior and adjust ctnetlink ordering after IPS_CONFIRMED.

Likely exposure

Exposure appears limited to Linux systems running affected kernel lines with netfilter conntrack and related ctnetlink or nfnetlink_queue paths in use. The bundle lists Linux kernel versions including 4.4, 6.1.28, 6.2.15, 6.3.2, and 6.4 as affected.

Exploitation context

The provided sources do not show active exploitation, public exploit availability, or KEV listing. The observable failure context is kernel conntrack timeout handling during packet queueing and ctnetlink operations, not a documented remote attack path.

Researcher notes

Evidence supports a logic bug in conntrack timeout conversion and ordering. The source bundle lacks CVSS, CWE, impact class, attacker prerequisites, and exploit evidence, so severity and practical exploitability remain uncertain.

Mitigation direction

  • Check Linux distribution kernel advisories for CVE-2023-53635.
  • Apply a stable kernel update containing the referenced netfilter conntrack fix.
  • Prioritize systems using conntrack, ctnetlink, NFQUEUE, or firewall packet inspection features.
  • Avoid claiming compensating controls unless confirmed by the kernel or distribution vendor.

Validation and detection

  • Inventory running kernel versions across Linux hosts and appliances.
  • Confirm whether netfilter conntrack and NFQUEUE-related features are enabled or used.
  • Compare installed kernel builds against distribution advisories for this CVE.
  • Review change records for the referenced stable kernel commits or backports.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
5Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxa4b4766c3cebb4018167e06b863d8e95b7274757, a4b4766c3cebb4018167e06b863d8e95b7274757, a4b4766c3cebb4018167e06b863d8e95b7274757, a4b4766c3cebb4018167e06b863d8e95b7274757unaffected
LinuxLinux4.4, 0, 6.1.28, 6.2.15, 6.3.2, 6.4affected
Weakness

CWE details

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