iptables: --syn flag bypass
Published Feb 15, 2014
7.5
HIGHCVSS 2.0
EPSS 2.74%
Description
extensions/libxt_tcp.c in iptables through 1.4.21 does not match TCP SYN+FIN packets in --syn rules, which might allow remote attackers to bypass intended firewall restrictions via crafted packets. NOTE: the CVE-2012-6638 fix makes this issue less relevant.
Affected products
No data.
No data.
Red Hat Enterprise Linux 5
iptables
Affected
Red Hat Enterprise Linux 6
iptables
Affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Enterprise Linux 5 | iptables | Affected | n/a |
| Red Hat Enterprise Linux 6 | iptables | Affected | n/a |
No package ranges for this CVE.
Remediation
Red Hat statement
This issue does affect Red Hat Enterprise Linux 5 and 6. The risks in breaking compatability associated with fixing this flaw outweigh the benefits of the fix, therefore Red Hat does not plan to fix this flaw in Red Hat Enterprise Linux 5 and 6. Please note that the remote DoS issue in the way how Linux kernel treats SYN+FIN flags set is being handled under different CVE, CVE-2012-6638, and is planned to be fixed in all affected Red Hat Enterprise Linux releases.
Red Hat mitigation
Instead of --syn use --tcp-flags SYN,RST,ACK SYN in your rulesets in case you want to also match packets with both SYN+FIN flags set.
Metrics
No CVSS v4.0 score for this CVE.
No CVSS v3.1 score for this CVE.
No CVSS v3.0 score for this CVE.
AV:N/AC:L/Au:N/C:P/I:P/A:P
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
2022–2026- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (10 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 2.74% (0.02737) | 85.61th | v5 (v2026.06.15) |
| Jun 15, 2026 | 2.85% (0.02849) | 84.82th | v5 (v2026.06.15) |
| Mar 17, 2025 | 0.29% (0.00290) | 50.32th | v4 (v2025.03.14) |
| Dec 12, 2024 | 0.48% (0.00484) | 76.77th | v3 (v2023.03.01) |
| Feb 8, 2024 | 0.48% (0.00484) | 75.25th | v3 (v2023.03.01) |
| Mar 7, 2023 | 0.48% (0.00484) | 72.22th | v3 (v2023.03.01) |
| Mar 6, 2023 | 1.05% (0.01055) | 52.13th | v2 (v2022.01.01) |
| Sep 17, 2022 | 1.05% (0.01055) | 50.47th | v2 (v2022.01.01) |
| Apr 1, 2022 | 1.05% (0.01055) | 48.43th | v2 (v2022.01.01) |
| Feb 4, 2022 | 1.05% (0.01055) | 27.52th | v2 (v2022.01.01) |
No CWE recorded.
References (5)
- http://www.spinics.net/lists/netfilter-devel/msg21248.html mailing-listx_refsource_MLISTPatchThird Party Advisory
- https://access.redhat.com/security/cve/CVE-2012-2663 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=826702 x_refsource_CONFIRMIssue TrackingMitigationPatchThird Party Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2012-2663
- https://www.cve.org/CVERecord?id=CVE-2012-2663
| Link | Providers | Tags |
|---|---|---|
| http://www.spinics.net/lists/netfilter-devel/msg21248.html | mailing-listx_refsource_MLISTPatchThird Party Advisory | |
| https://access.redhat.com/security/cve/CVE-2012-2663 | Vendor Advisory | |
| https://bugzilla.redhat.com/show_bug.cgi?id=826702 | x_refsource_CONFIRMIssue TrackingMitigationPatchThird Party Advisory | |
| https://nvd.nist.gov/vuln/detail/CVE-2012-2663 | ||
| https://www.cve.org/CVERecord?id=CVE-2012-2663 |
Change history (0)
No recorded changes yet.