CVE-2021-1224: Multiple Cisco products are affected by a vulnerability with TCP Fast Open (TFO) when used in conjunction with

Q: How do I fix CVE-2021-1224?

secure firewall management center: downgrade or apply the listed mitigation; secure firewall threat defense: upgrade to 6.7.0; ios xe: upgrade to 17.4.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-1224 being exploited?

CVE-2021-1224 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-1224 affect?

CVE-2021-1224 affects secure firewall management center, secure firewall threat defense, ios xe. Severity is medium (CVSS 5.8). Multiple Cisco products are affected by a vulnerability with TCP Fast Open (TFO) when used in conjunction with the Snort detection engine that could allow an unauthenticated, remote attacker to bypass a configured file policy for HTTP. The

Q: How urgent is CVE-2021-1224?

Priority 46/100. Remotely exploitable, no login, no user action

This month

MEDIUM 5.8REMOTEDOWNGRADEUPGRADEUPGRADE

CVE-2021-1224 is a medium-severity flaw (CVSS 5.8) affecting secure firewall management center, secure firewall threat defense, ios xe. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Multiple Cisco products are affected by a vulnerability with TCP Fast Open (TFO) when used in conjunction with the Snort detection engine that could allow an unauthenticated, remote attacker to bypass a configured file policy for HTTP. The vulnerability is due to incorrect detection of the HTTP payload if it is contained at least partially within the TFO connection handshake. An attacker could exploit this vulnerability by sending crafted TFO pac

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.8 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.0% (top 19%)
CISA exploited list	No
Weakness	CWE-693
Published	2021-01-13
Last modified	2026-08-11

Publisher (CNA): Cisco Systems, Inc. · Vendor: cisco · snort

Last updated 2026-08-11 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-01-13 22:15 UTCPublished CVE record published
2026-08-11 19:37 UTCUpdated Record last modified

cisco secure firewall management center DOWNGRADE

Affected: 2.9.14.0 · 2.9.15 · 2.9.16 · 2.9.17 · 2.9.18 · 3.0.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.9.14.0

1. Check installed version

apt-cache policy secure-firewall-management-center || rpm -q secure-firewall-management-center || secure-firewall-management-center --version

2. No fixed release: DOWNGRADE to a release before 2.9.14.0 (Debian / Ubuntu)

apt-cache madison secure-firewall-management-center sudo apt install secure-firewall-management-center=<VERSION_BEFORE_2.9.14.0> sudo apt-mark hold secure-firewall-management-center

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list secure-firewall-management-center sudo dnf downgrade secure-firewall-management-center-<VERSION_BEFORE_2.9.14.0> sudo dnf versionlock add secure-firewall-management-center

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

cisco secure firewall threat defense UPGRADE

Affected: < 6.7.0

Fixed in: 6.7.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy secure-firewall-threat-defense || rpm -q secure-firewall-threat-defense || secure-firewall-threat-defense --version

2. UPGRADE to 6.7.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade secure-firewall-threat-defense

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade secure-firewall-threat-defense

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

cisco ios xe UPGRADE

Affected: < 17.4.1

Fixed in: 17.4.1

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

snort snort UPGRADE

Affected: < 2.9.17

Fixed in: 2.9.17

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy snort || rpm -q snort || snort --version

2. UPGRADE to 2.9.17 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade snort

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade snort

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

cisco meraki mx64 firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

cisco meraki mx64w firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-1224?

secure firewall management center: downgrade or apply the listed mitigation; secure firewall threat defense: upgrade to 6.7.0; ios xe: upgrade to 17.4.1. Exact commands for each OS are on this page.

Is CVE-2021-1224 being exploited?

CVE-2021-1224 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-1224 affect?

CVE-2021-1224 affects secure firewall management center, secure firewall threat defense, ios xe. Severity is medium (CVSS 5.8). Multiple Cisco products are affected by a vulnerability with TCP Fast Open (TFO) when used in conjunction with the Snort detection engine that could allow an unauthenticated, remote attacker to bypass a configured file policy for HTTP. The

How urgent is CVE-2021-1224?

Priority 46/100. Remotely exploitable, no login, no user action

Software pages

iOS vulnerabilities · Cisco IOS XE vulnerabilities · Cisco vulnerabilities · Suricata and Snort vulnerabilities

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References

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