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CVE-2026-20221— Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities

Quick assessment

Affected
Cisco Cisco Cyber Vision
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

多个 Cisco 产品受 Snort 3 检测引擎中通用路由封装（GRE）隧道解封装功能漏洞的影响。该漏洞可能使未经身份验证的远程攻击者导致 Snort 3 检测引擎意外重启。 此漏洞源于对嵌套 GRE 流量的处理不当。攻击者可通过向受影响设备发送特制的 GRE 载荷来利用该漏洞。成功利用后，攻击者可触发 Snort 3 检测引擎意外重新加载，根据设备配置不同，可能导致检测绕过或服务拒绝（DoS）状况。更多信息请参阅本通告的相关章节。Snort 3 检测引擎将自动重启，无需人工干预。

CVSS 5.8 · Medium
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I. Basic Information for CVE-2026-20221

Vulnerability Information
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Vulnerability Title
Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities
Source: CVE Program / CVE List V5
Vulnerability Description
Multiple Cisco products are affected by a vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause an unexpected restart of the Snort 3 Detection Engine. This vulnerability is due to improper handling of nested GRE traffic. An attacker could exploit this vulnerability by sending a crafted GRE payload through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 Detection Engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. For more information, see the section of this advisory. The Snort 3 Detection Engine will restart automatically. No manual intervention is required.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
空指针解引用
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Cisco Cisco Cyber Vision 3.0.0 -
Cisco Cisco Open Source Snort3 3.12.2.0 -
Cisco Cisco Secure Firewall Threat Defense (FTD) Software 7.0.0 -
Cisco Cisco Umbrella Insights Virtual Appliance 2.6.0 -
Cisco Cisco UTD SNORT IPS Engine Software 3.17.1S -

II. Public POCs for CVE-2026-20221

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III. Intelligence Information for CVE-2026-20221

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Other References for CVE-2026-20221 (1)

Same Patch Batch · Cisco · 2026-10-21 · 34 CVEs total

CVE-2026-76466 9.8 CRITICAL Cisco Expressway Series Remote Code Execution Vulnerability
CVE-2026-76473 9.8 CRITICAL Cisco Unified Communications Products Hardening Release: October 2026 - Improper control o
CVE-2026-76474 9.8 CRITICAL Cisco Unified Communications Products Hardening Release: October 2026 - Improper Authentic
CVE-2026-76475 9.3 CRITICAL Cisco Unified Communications Products Hardening Release: October 2026 - Cross-site Scripti
CVE-2026-20043 9.0 CRITICAL Multiple Cisco Products Snort 3 Software Hardening Release: October 2026
CVE-2026-76477 8.8 HIGH Cisco Unified Communications Products Hardening Release: October 2026 - Injection Vulnerab
CVE-2026-76476 8.8 HIGH Cisco Unified Communications Products Hardening Release: October 2026 - Improper Input Val
CVE-2026-76478 8.8 HIGH Cisco Unified Communications Products Hardening Release: October 2026 - Improper Access Co
CVE-2026-76490 8.6 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - Out-of-bounds Write Vul
CVE-2026-76524 7.8 HIGH Open Source Snort 3 Control Channel Socket Aribitrary Command Execution Vulnerability
CVE-2026-20291 7.8 HIGH Multiple Cisco Products Snort 3 Software Hardening Release: October 2026
CVE-2026-76479 7.8 HIGH Cisco Unified Communications Products Hardening Release: October 2026 - Path Traversal Vul
CVE-2026-76494 7.8 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - Code Injection Vulnerab
CVE-2026-76495 7.8 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - Incorrect Permission As
CVE-2026-76481 7.5 HIGH Cisco Unified Communications Products Hardening Release: October 2026 - Improper Check or
CVE-2026-76491 7.5 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - Denial of Service Vulne
CVE-2026-76492 7.5 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - NULL Pointer Vulnerabil
CVE-2026-76505 7.5 HIGH Cisco IOS XR Software for ASR 9000 Series Routers IPv4 Unicast Packets Denial of Service V
CVE-2026-76493 7.5 HIGH Cisco Expressway Series Software Hardening Release: October 2026 - Uncaught Exception Vuln
CVE-2026-20236 7.5 HIGH Multiple Cisco Products Snort 3 Software Hardening Release: October 2026

Showing top 20 of 34 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Cisco Cyber Vision
Same vendor: Cisco
Same weakness: CWE-476

V. Comments for CVE-2026-20221

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