Multiple Cisco Products Snort Application Detection Engine Policy Bypass Vulnerability

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Summary

CVECVE-2021-1236
StatePUBLISHED
Assignercisco
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-01-13 22:15:20 UTC
Updated2026-08-11 19:37:30 UTC
DescriptionMultiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS: 0.021460000 probability, percentile 0.804300000 (date 2026-08-12)

Problem Types: CWE-670 | CWE-670 CWE-670

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
3.0[email protected]Secondary4MEDIUMCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
3.0CNADECLARED4MEDIUMCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
2.0[email protected]Primary5AV:N/AC:L/Au:N/C:N/I:P/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.0 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

CVSS v2.0 Breakdown

Access Vector
Network
Access Complexity
Low
Authentication
None
Confidentiality
None
Integrity
Partial
Availability
None

AV:N/AC:L/Au:N/C:N/I:P/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Hardware Cisco 1100-4p Integrated Services Router - All All All
Hardware Cisco 1100-8p Integrated Services Router - All All All
Hardware Cisco 1101-4p Integrated Services Router - All All All
Hardware Cisco 1109-2p Integrated Services Router - All All All
Hardware Cisco 1109-4p Integrated Services Router - All All All
Hardware Cisco 1111x-8p Integrated Services Router - All All All
Hardware Cisco 4221 Integrated Services Router - All All All
Hardware Cisco 4321 Integrated Services Router - All All All
Hardware Cisco 4331 Integrated Services Router - All All All
Hardware Cisco 4351 Integrated Services Router - All All All
Hardware Cisco 4431 Integrated Services Router - All All All
Hardware Cisco 4451-x Integrated Services Router - All All All
Hardware Cisco 4461 Integrated Services Router - All All All
Hardware Cisco Csr 1000v - All All All
Operating System Cisco Ios Xe All All All All
Hardware Cisco Isa 3000 - All All All
Application Cisco Secure Firewall Management Center 2.9.14.0 All All All
Application Cisco Secure Firewall Management Center 2.9.14.14 All All All
Application Cisco Secure Firewall Management Center 2.9.15 All All All
Application Cisco Secure Firewall Management Center 2.9.16 All All All
Application Cisco Secure Firewall Management Center 2.9.17 All All All
Application Cisco Secure Firewall Threat Defense All All All All
Application Snort Snort All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Cisco Cisco Firepower Threat Defense Software affected n/a Not specified

References

ReferenceSourceLinkTags
Debian -- Security Information -- DSA-5354-1 snort af854a3a-2127-422b-91ae-364da2661108 www.debian.org
Multiple Cisco Products Snort Application Detection Engine Policy Bypass Vulnerability af854a3a-2127-422b-91ae-364da2661108 tools.cisco.com Vendor Advisory
[SECURITY] [DLA 3317-1] snort security update af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

Exploits

CNA: The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

Legacy QID Mappings

  • 179407 Debian Security Update for snort (CVE-2021-1236)
  • 181554 Debian Security Update for snort (DLA 3317-1)
  • 181678 Debian Security Update for snort (DSA 5354-1)
  • 317250 Multiple Cisco Products Snort Application Detection Engine Policy Bypass Vulnerability (cisco-sa-snort-app-bypass-cSBYCATq)

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