8.2
HIGH CVSS 3.1
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 :

Oct. 19, 2026, 9:17 p.m.

Remotely Exploit :

Yes !

Source :

416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products

The following products are affected by CVE-2026-63913 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Linux linux_kernel
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 134c704f-9b21-4f2e-91b3-4a467353bcc0
CVSS 3.1 HIGH 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
Update the Linux kernel to fix conntrack TCP state machine vulnerability.
  • Update the Linux kernel.
  • Apply the netfilter: conntrack: tcp fix.
  • Ensure RST packets are validated.
  • Tighten state transition logic.
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.

CAPEC-3: Using Leading 'Ghost' Character Sequences to Bypass Input Filters Using Leading 'Ghost' Character Sequences to Bypass Input Filters CAPEC-7: Blind SQL Injection Blind SQL Injection CAPEC-8: Buffer Overflow in an API Call Buffer Overflow in an API Call CAPEC-9: Buffer Overflow in Local Command-Line Utilities Buffer Overflow in Local Command-Line Utilities CAPEC-10: Buffer Overflow via Environment Variables Buffer Overflow via Environment Variables CAPEC-13: Subverting Environment Variable Values Subverting Environment Variable Values CAPEC-14: Client-side Injection-induced Buffer Overflow Client-side Injection-induced Buffer Overflow CAPEC-22: Exploiting Trust in Client Exploiting Trust in Client CAPEC-23: File Content Injection File Content Injection CAPEC-24: Filter Failure through Buffer Overflow Filter Failure through Buffer Overflow CAPEC-28: Fuzzing Fuzzing CAPEC-31: Accessing/Intercepting/Modifying HTTP Cookies Accessing/Intercepting/Modifying HTTP Cookies CAPEC-42: MIME Conversion MIME Conversion CAPEC-43: Exploiting Multiple Input Interpretation Layers Exploiting Multiple Input Interpretation Layers CAPEC-45: Buffer Overflow via Symbolic Links Buffer Overflow via Symbolic Links CAPEC-46: Overflow Variables and Tags Overflow Variables and Tags CAPEC-47: Buffer Overflow via Parameter Expansion Buffer Overflow via Parameter Expansion CAPEC-52: Embedding NULL Bytes Embedding NULL Bytes CAPEC-53: Postfix, Null Terminate, and Backslash Postfix, Null Terminate, and Backslash CAPEC-63: Cross-Site Scripting (XSS) Cross-Site Scripting (XSS) CAPEC-64: Using Slashes and URL Encoding Combined to Bypass Validation Logic Using Slashes and URL Encoding Combined to Bypass Validation Logic CAPEC-67: String Format Overflow in syslog() String Format Overflow in syslog() CAPEC-71: Using Unicode Encoding to Bypass Validation Logic Using Unicode Encoding to Bypass Validation Logic CAPEC-72: URL Encoding URL Encoding CAPEC-73: User-Controlled Filename User-Controlled Filename CAPEC-78: Using Escaped Slashes in Alternate Encoding Using Escaped Slashes in Alternate Encoding CAPEC-79: Using Slashes in Alternate Encoding Using Slashes in Alternate Encoding CAPEC-80: Using UTF-8 Encoding to Bypass Validation Logic Using UTF-8 Encoding to Bypass Validation Logic CAPEC-81: Web Server Logs Tampering Web Server Logs Tampering CAPEC-83: XPath Injection XPath Injection CAPEC-85: AJAX Footprinting AJAX Footprinting CAPEC-88: OS Command Injection OS Command Injection CAPEC-101: Server Side Include (SSI) Injection Server Side Include (SSI) Injection CAPEC-104: Cross Zone Scripting Cross Zone Scripting CAPEC-108: Command Line Execution through SQL Injection Command Line Execution through SQL Injection CAPEC-109: Object Relational Mapping Injection Object Relational Mapping Injection CAPEC-110: SQL Injection through SOAP Parameter Tampering SQL Injection through SOAP Parameter Tampering CAPEC-120: Double Encoding Double Encoding CAPEC-135: Format String Injection Format String Injection CAPEC-136: LDAP Injection LDAP Injection CAPEC-153: Input Data Manipulation Input Data Manipulation CAPEC-182: Flash Injection Flash Injection CAPEC-209: XSS Using MIME Type Mismatch XSS Using MIME Type Mismatch CAPEC-230: Serialized Data with Nested Payloads Serialized Data with Nested Payloads CAPEC-231: Oversized Serialized Data Payloads Oversized Serialized Data Payloads CAPEC-250: XML Injection XML Injection CAPEC-261: Fuzzing for garnering other adjacent user/sensitive data Fuzzing for garnering other adjacent user/sensitive data CAPEC-267: Leverage Alternate Encoding Leverage Alternate Encoding CAPEC-473: Signature Spoof Signature Spoof CAPEC-588: DOM-Based XSS DOM-Based XSS CAPEC-664: Server Side Request Forgery Server Side Request Forgery

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

Published Date: Aug 07, 2026 (2 months, 3 weeks ago)

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 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Oct. 19, 2026

    Action Type Old Value New Value
    Added CWE CWE-20
  • CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    Oct. 16, 2026

    Action Type Old Value New Value
    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
    Removed Reference https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656
    Removed Reference https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77
    Removed Reference https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238
    Removed Reference https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f
    Removed Reference https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
    Removed Reference https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8
    Removed Reference https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58
    Removed Reference https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Oct. 16, 2026

    Action Type Old Value New Value
    Added SSVC {'id': 'CVE-2026-63913', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-10-16T15:33:11.442709Z'}
  • 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
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.