Multiple Cisco Products Snort TCP Fast Open File Policy Bypass Vulnerability (CVE-2021-1224)
Published Last modified Sources: Debian, CVE.org
What is affected, what to do
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.
Update Cisco Firepower Threat Defense Software to version 6.7.0, Cisco IOS XE to version 17.4.1, Snort Snort to version 2.9.17.
- Affected
- Cisco Firepower Management Center
eq 2.9.14.0..2.9.14.0 - Cisco Firepower Management Center
eq 2.9.15..2.9.15 - Cisco Firepower Management Center
eq 2.9.16..2.9.16 - Cisco Firepower Management Center
eq 2.9.17..2.9.17 - Cisco Firepower Management Center
eq 2.9.18..2.9.18 - Cisco Firepower Management Center
eq 3.0.1..3.0.1 - Cisco Firepower Threat Defense Software
lt *..6.7.0 - Cisco IOS XE
lt *..17.4.1 - Snort Snort
lt *..2.9.17
- Cisco Firepower Management Center
- Fixed in
- Cisco Firepower Threat Defense Software
6.7.0 - Cisco IOS XE
17.4.1 - Snort Snort
2.9.17
- Cisco Firepower Threat Defense Software
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Metrics
5.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
5.8
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Debian, CVE.org
2.1 %
EPSS score
Moderate — model estimates 1-10% exploitation likelihood.
Source: FIRST EPSS, percentile 81.1
Show all metrics
- Severity
- Medium
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 81.66 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 5.8 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 5.8
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 2.1 %
- Moderate — model estimates 1-10% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 81.1
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
- CISA assessment (SSVC)
- Exploitation: none known · automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 8 November 2024
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-693
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
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 packets with an HTTP payload through an affected device. A successful exploit could allow the attacker to bypass configured file policy for HTTP packets and deliver a malicious payload.
Source: Debian Security Advisories, cvelistv5, NVD (NIST)
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| cisco | secure_firewall_management_center |
|
|
| cisco | secure_firewall_threat_defense |
|
|
| snort | snort |
|
|
Vendors and products
- Cisco Cisco IOS XE SD-WAN Software
- Cisco Meraki Mx100 Firmware
- Cisco Meraki Mx250 Firmware
- Cisco Meraki Mx450 Firmware
- Cisco Meraki Mx64 Firmware
- Cisco Meraki Mx64w Firmware
- Cisco Meraki Mx67c Firmware
- Cisco Meraki Mx67 Firmware
- Cisco Meraki Mx67w Firmware
- Cisco Meraki Mx68cw Firmware
- Cisco Meraki Mx68 Firmware
- Cisco Meraki Mx68w Firmware
Affected operating systems
| Linux | debian | snort | bullseye |
| Mobile | cisco | ios_xe | — |
| Other | cisco | meraki_mx100_firmware | — |
| Other | cisco | meraki_mx250_firmware | — |
| Other | cisco | meraki_mx450_firmware | — |
| Other | cisco | meraki_mx64_firmware | — |
| Other | cisco | meraki_mx64w_firmware | — |
| Other | cisco | meraki_mx67_firmware | — |
| Other | cisco | meraki_mx67c_firmware | — |
| Other | cisco | meraki_mx67w_firmware | — |
| Other | cisco | meraki_mx68_firmware | — |
| Other | cisco | meraki_mx68cw_firmware | — |
| Other | cisco | meraki_mx68w_firmware | — |
| Other | cisco | meraki_mx84_firmware | — |
Weakness classes (CWE)
CWE-693Protection Mechanism Failure
Pillar
The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.
Entry at MITRE CWE-693
References & sources
- tools.cisco.com20210113 Multiple Cisco Products Snort TCP Fast Open File Policy Bypass VulnerabilityVendor advisory
- lists.debian.org[debian-lts-announce] 20230210 [SECURITY] [DLA 3317-1] snort security updateMailing list
- debian.orgDSA-5354Vendor advisory
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Product identifiers remappedNVD
Product mapping changed:- Cisco Firepower Threat Defense Software (after 6.7.0)
Show the original change
Individual changes of this event as published by NVD Type Action Before After Product configuration changed OR *cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:* versions from (excluding) 6.7.0OR *cpe:2.3:a:cisco:secure_firewall_threat_defense:*:*:*:*:*:*:*:* versions from (excluding) 6.7.0Source identifier: nvd@nist.gov
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-1224"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-1224.svg?lang=en" alt="CVE-2021-1224 – NEOSEC Intel" height="20"></a>