CVE-2026-63913
netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check
No known exploitation. EPSS puts it in the 60th percentile. No fix published yet.
What to do
No fixed build or workaround is published yet. Limit exposure and watch for a patch.
What it is
From the CVE record
In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
1.0% chance of exploitation activity in the next 30 days, which ranks it in the 60th percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
7 events over 50 days, from the signal feeds we watch.
- Analysis publishedNatJack: The Same NAT Flaw Got Windows and Linux Patched — Cisco and Apple Call It a Feature
- Record updated
- OpenVAS check added
- Record updated
- Publishedrecord updated
- OpenVAS check added
Affected products
Technical detail
CVSS 3.1 vector
Open in the CVSS calculatorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Scored 8.2 by NVD.
How it is reached
- Attack Vector NetworkExploitable remotely over the network without any special conditions
- Attack Complexity LowNo special conditions — the attack can be reliably reproduced
- Privileges Required NoneNo authentication required — anyone can exploit this
- User Interaction NoneNo user interaction needed — fully automated exploitation
Scope
- Scope UnchangedImpact is limited to the vulnerable component itself
Impact if exploited
- Confidentiality NoneNo confidentiality impact
- Integrity LowData modification is possible but limited in scope or consequence
- Availability HighTotal denial of service — the component is completely unavailable
Sources
References in the record
- git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656
- git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238
- git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0
And 5 more references. See all after sign-in
In the news
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