CVE-2026-63913
netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check
Description
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.
INFO
Published Date :
July 19, 2026, 4:17 p.m.
Last Modified :
July 27, 2026, 5:44 p.m.
Remotely Exploit :
Yes !
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
Solution
- Update the Linux kernel.
- Apply the netfilter: conntrack: tcp fix.
- Ensure RST packets are validated.
- Tighten state transition logic.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-63913.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-63913 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-63913
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-63913 vulnerability anywhere in the article.
-
The Hacker News
New NatJack Attacks Hijack TCP Sessions and Spoof DNS by Manipulating NAT Tables
Security researcher Malcolm Stagg has disclosed a new attack class called NatJack that manipulates network address translation (NAT) connection state to hijack active TCP sessions, spoof DNS responses ... Read more
The following table lists the changes that have been made to the
CVE-2026-63913 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 20, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 19, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': '2006979a15af5404bf932a325357683c0bac1656', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': '6476c17d536dbd321c073242e762ddb2713a1238', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': 'f5547bebc416d56f56fb5b86dc20aabfa42165a0', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': '2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': 'f206def4e86d810f927ba1d8e322ea72b29bce58', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': 'b98ab51c45c5608a1c19ce7fd17a3032469bb83f', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': 'd67c6adee8d1b65330d0174c4c367faba14e80a8', 'versionType': 'git'}, {'status': 'affected', 'version': '9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1', 'lessThan': 'bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a', 'versionType': 'git'}], 'programFiles': ['net/netfilter/nf_conntrack_proto_tcp.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '2.6.15'}, {'status': 'unaffected', 'version': '0', 'lessThan': '2.6.15', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '5.10.259', 'versionType': 'semver', 'lessThanOrEqual': '5.10.*'}, {'status': 'unaffected', 'version': '5.15.210', 'versionType': 'semver', 'lessThanOrEqual': '5.15.*'}, {'status': 'unaffected', 'version': '6.1.176', 'versionType': 'semver', 'lessThanOrEqual': '6.1.*'}, {'status': 'unaffected', 'version': '6.6.143', 'versionType': 'semver', 'lessThanOrEqual': '6.6.*'}, {'status': 'unaffected', 'version': '6.12.93', 'versionType': 'semver', 'lessThanOrEqual': '6.12.*'}, {'status': 'unaffected', 'version': '6.18.35', 'versionType': 'semver', 'lessThanOrEqual': '6.18.*'}, {'status': 'unaffected', 'version': '7.0.12', 'versionType': 'semver', 'lessThanOrEqual': '7.0.*'}, {'status': 'unaffected', 'version': '7.1', 'versionType': 'original_commit_for_fix', 'lessThanOrEqual': '*'}], 'programFiles': ['net/netfilter/nf_conntrack_proto_tcp.c'], 'defaultStatus': 'affected'}] Added Description 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. Added Reference https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656 Added Reference https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77 Added Reference https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238 Added Reference https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f Added Reference https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a Added Reference https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8 Added Reference https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58 Added Reference https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0