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Full vulnerability report · 2025
CVE-2023-53635High confidence

netfilter: conntrack: fix wrong ct->timeout value

Linux · Linux

8.2HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

9 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · standard archivelinux-azure-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-gcp-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-hwe-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-intelAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-lowlatency-hwe-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-oem-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-raspi-realtimeAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-realtimeAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-riscvAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 11 Sept 2026
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2025-31983

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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.

What

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.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → vulnerable operation → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration.
CWE not yet assigned
CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.ILowIntegrity impact: A successful attack can cause a limited loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticated
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-0349Dell Avamar und NetWorker: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Dell Avamar und Dell NetWorker ausnutzen, um Angriffe zu starten, die die Integrität, Vertraulichkeit und Verfügbarkeit von Systemen beeinträchtigen.

Official advisory ↗
BSI · German · WID-SEC-2025-2229Linux Kernel: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen Denial of Service Angriff durchzuführen und andere nicht näher spezifizierte Angriffe durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20251008Security Bulletin 08 Oct 2025

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 08 Oct 2025, published on 8 October 2025. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0326Multiples vulnérabilités dans les produits VMware

ord?id=CVE-2023-53588 Référence CVE CVE-2023-53596 https://www.cve.org/CVERecord?id=CVE-2023-53596 Référence CVE CVE-2023-53602 https://www.cve.org/CVERecord?id=CVE-2023-53602 Référence CVE CVE-2023-53609 https://www.cve.org/CVERecord?id=CVE-2023-53609 Référence CVE CVE-2023-53620 https://www.cve.org/CVERecord?id=CVE-2023-53620 Référence CVE CVE-2023-53627 https://www.cve.org/CVERecord?id=CVE-2023-53627 Référence CVE CVE-2023-53628 https://www.cve.org/CVERecord?id=CVE-2023-53628 Référence CVE CVE-2023-53629 https://www.cve.org/CVERecord?id=CVE-2023-53629 Référence CVE CVE-2023-5363 https://www.cve.org/CVERecord?id=CVE-2023-5363 Référence CVE CVE-2023-53635 https://www.cve.org/CVERecord?id=CVE-2023-53635 Référence CVE CVE-2023-53647 https://www.cve.org/CVERecord?id=CVE-2023-53647 Référence CVE CVE-2023-53651 https://www.cve.org/CVERecord?id=CVE-2023-53651 Référence CVE CVE-2023-53657 https://www.cve.org/CVERecord?id=CVE-2023-53657 Référence CVE CVE-2023-53662 https://www.cve.org/CVERecord?id=CVE-2023-53662 Référence CVE CVE-2023-53671 https://www.cve.org/CVERecord?id=CVE-2023-53671 Référence CVE CVE-2023-53673 https://www.cve.org/CVERecord?id=CVE-2023-53673 Référence CVE CVE-2023-53682 https://www.cve.org/CVERecord?id=CVE-2023-53682 Référence CVE CVE-2023-53685 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0316Multiples vulnérabilités dans les produits VMware

ord?id=CVE-2023-53588 Référence CVE CVE-2023-53596 https://www.cve.org/CVERecord?id=CVE-2023-53596 Référence CVE CVE-2023-53602 https://www.cve.org/CVERecord?id=CVE-2023-53602 Référence CVE CVE-2023-53609 https://www.cve.org/CVERecord?id=CVE-2023-53609 Référence CVE CVE-2023-53620 https://www.cve.org/CVERecord?id=CVE-2023-53620 Référence CVE CVE-2023-53627 https://www.cve.org/CVERecord?id=CVE-2023-53627 Référence CVE CVE-2023-53628 https://www.cve.org/CVERecord?id=CVE-2023-53628 Référence CVE CVE-2023-53629 https://www.cve.org/CVERecord?id=CVE-2023-53629 Référence CVE CVE-2023-5363 https://www.cve.org/CVERecord?id=CVE-2023-5363 Référence CVE CVE-2023-53635 https://www.cve.org/CVERecord?id=CVE-2023-53635 Référence CVE CVE-2023-53647 https://www.cve.org/CVERecord?id=CVE-2023-53647 Référence CVE CVE-2023-53651 https://www.cve.org/CVERecord?id=CVE-2023-53651 Référence CVE CVE-2023-53657 https://www.cve.org/CVERecord?id=CVE-2023-53657 Référence CVE CVE-2023-53662 https://www.cve.org/CVERecord?id=CVE-2023-53662 Référence CVE CVE-2023-53671 https://www.cve.org/CVERecord?id=CVE-2023-53671 Référence CVE CVE-2023-53673 https://www.cve.org/CVERecord?id=CVE-2023-53673 Référence CVE CVE-2023-53682 https://www.cve.org/CVERecord?id=CVE-2023-53682 Référence CVE CVE-2023-53685 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2025-AVI-1047Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2023-53618 Référence CVE CVE-2023-53619 https://www.cve.org/CVERecord?id=CVE-2023-53619 Référence CVE CVE-2023-53620 https://www.cve.org/CVERecord?id=CVE-2023-53620 Référence CVE CVE-2023-53621 https://www.cve.org/CVERecord?id=CVE-2023-53621 Référence CVE CVE-2023-53622 https://www.cve.org/CVERecord?id=CVE-2023-53622 Référence CVE CVE-2023-53624 https://www.cve.org/CVERecord?id=CVE-2023-53624 Référence CVE CVE-2023-53631 https://www.cve.org/CVERecord?id=CVE-2023-53631 Référence CVE CVE-2023-53632 https://www.cve.org/CVERecord?id=CVE-2023-53632 Référence CVE CVE-2023-53633 https://www.cve.org/CVERecord?id=CVE-2023-53633 Référence CVE CVE-2023-53635 https://www.cve.org/CVERecord?id=CVE-2023-53635 Référence CVE CVE-2023-53638 https://www.cve.org/CVERecord?id=CVE-2023-53638 Référence CVE CVE-2023-53644 https://www.cve.org/CVERecord?id=CVE-2023-53644 Référence CVE CVE-2023-53645 https://www.cve.org/CVERecord?id=CVE-2023-53645 Référence CVE CVE-2023-53646 https://www.cve.org/CVERecord?id=CVE-2023-53646 Référence CVE CVE-2023-53647 https://www.cve.org/CVERecord?id=CVE-2023-53647 Référence CVE CVE-2023-53648 https://www.cve.org/CVERecord?id=CVE-2023-53648 Référence CVE CVE-2023-53649 https://www.cve.org/CVERecord?id=CVE-2023-53649 Référence CVE CVE-2023-53650 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2025-025778LinuxのLinux Kernelにおける不特定の脆弱性

Linuxカーネルにおいて、以下の脆弱性が修正されました。netfilterのconntrackに関する誤ったct-timeout値の問題です。struct nf_connのtimeoutは、conntrackが確認される前は時間間隔を示し、確認後はタイムスタンプとなります。確認されていないconntrackのtimeoutは、ctnetlink_change_timeout()の呼び出しによって設定されていました。その結果、nfct_time_stampがct-timeoutに二重に加算されていました。また、ctnetlink_dump_timeout()の呼び出しによりtimeoutを取得する際に、nfct_time_stampが誤って減算されていました。呼び出しトレースは以下の通りです: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。処理は二つの場合に分かれます。ひとつは__nf_ct_set_timeout()内でのct-timeoutの設定、もうひとつはctnetlink_dump_timeout()内でのct-timeoutの取得です。Pabloによる追記では、IP_CONFIRMEDフラグが設定された後にtimeoutを設定するようにctnetlinkを更新しなければ、ctnetlink経由のconntrack作成が正常に動作しなくなる旨が説明されています。このパッチで説明された問題は、nfnetlink_queue conntrackサポートの導入以降に発生しているため、stableカーネルでこの修正を取り込む際には十分古いFixesタグを選択してください。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Linux: a4b4766c3cebb4018167e06b863d8e95b7274757 < 80c5ba0078e20d926d11d0778f9a43902664ebf0, a4b4766c3cebb4018167e06b863d8e95b7274757 < ff5e4ac8dd7be7f1faba955c5779a68571eeb0f8, a4b4766c3cebb4018167e06b863d8e95b7274757 < f612ae1ab4793701caf39386fb3b7f4b3ef44e48, a4b4766c3cebb4018167e06b863d8e95b7274757 < 73db1b8f2bb6725b7391e85aab41fdf592b3c0c1, 4.4
Fixed
Linux: < 4.4, 6.1.28 ≤ 6.1.*, 6.2.15 ≤ 6.2.*, 6.3.2 ≤ 6.3.*, 6.4 ≤ *
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 7 Oct 2025 · Last source change 5 Aug 2026, 09:15 UTC · CWE not yet assigned

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2025-31983
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceUnavailable
NVD statusNVD modified after enrichment

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2023-53635 · cve.blacktree.nl