CVE-2026-20084Network attack vector

Unauthenticated denial of service via BOOTP VLAN leakage

Published Mar 25, 2026 · Updated Mar 25, 2026

Denial of service in DHCP snooping in Cisco IOS XE Software allows remote attackers to make affected switches unreachable via BOOTP packets. On Catalyst 9000 Series Switches, the DHCP snooping path forwards unicast or broadcast BOOTP requests across VLANs when an SVI helper targets a subinterface with a native VLAN. When DHCP snooping covers that native VLAN, the leaked traffic drives CPU utilization high enough to block console and remote management and stop packet forwarding.

CVSS severity8.6
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in DHCP snooping in Cisco IOS XE Software allows remote attackers to make affected switches unreachable via BOOTP packets. On Catalyst 9000 Series Switches, the DHCP snooping path forwards unicast or broadcast BOOTP requests across VLANs when an SVI helper targets a subinterface with a native VLAN. When DHCP snooping covers that native VLAN, the leaked traffic drives CPU utilization high enough to block console and remote management and stop packet forwarding.

The record

CVE
CVE-2026-20084
Published
Mar 25, 2026
Updated
Mar 25, 2026
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.10.1
  2. Affected versionversion=16.10.1e
  3. Affected versionversion=16.10.1s
  4. Affected versionversion=16.11.1
  5. Affected versionversion=16.11.1b
  6. Affected versionversion=16.11.1s
  7. Affected versionversion=16.12.1
  8. Affected versionversion=16.12.1c
  9. Affected versionversion=16.12.1s
  10. Affected versionversion=16.12.2
  11. Affected versionversion=16.12.2s
  12. Affected versionversion=16.12.3
  13. Affected versionversion=16.12.3a
  14. Affected versionversion=16.12.3s
  15. Affected versionversion=16.12.4
  16. Affected versionversion=16.12.4a
  17. Affected versionversion=16.12.5
  18. Affected versionversion=16.12.5b
  19. Affected versionversion=16.12.6
  20. Affected versionversion=16.12.6a
  21. Affected versionversion=16.12.7
  22. Affected versionversion=16.12.8
  23. Affected versionversion=16.6.1
  24. Affected versionversion=16.6.10
  25. Affected versionversion=16.6.2
  26. Affected versionversion=16.6.3
  27. Affected versionversion=16.6.4
  28. Affected versionversion=16.6.4a
  29. Affected versionversion=16.6.5
  30. Affected versionversion=16.6.6
  31. Affected versionversion=16.6.7
  32. Affected versionversion=16.6.8
  33. Affected versionversion=16.6.9
  34. Affected versionversion=16.7.1
  35. Affected versionversion=16.8.1
  36. Affected versionversion=16.8.1a
  37. Affected versionversion=16.8.1s
  38. Affected versionversion=16.9.1
  39. Affected versionversion=16.9.1s
  40. Affected versionversion=16.9.2
  41. Affected versionversion=16.9.3
  42. Affected versionversion=16.9.4
  43. Affected versionversion=16.9.5
  44. Affected versionversion=16.9.6
  45. Affected versionversion=16.9.7
  46. Affected versionversion=16.9.8
  47. Affected versionversion=17.10.1
  48. Affected versionversion=17.10.1b
  49. Affected versionversion=17.1.1
  50. Affected versionversion=17.11.1
  51. Affected versionversion=17.1.1s
  52. Affected versionversion=17.1.1t
  53. Affected versionversion=17.12.1
  54. Affected versionversion=17.12.1z5
  55. Affected versionversion=17.12.2
  56. Affected versionversion=17.12.3
  57. Affected versionversion=17.12.4
  58. Affected versionversion=17.12.5
  59. Affected versionversion=17.1.3
  60. Affected versionversion=17.13.1
  61. Affected versionversion=17.14.1
  62. Affected versionversion=17.15.1
  63. Affected versionversion=17.15.2
  64. Affected versionversion=17.15.2b
  65. Affected versionversion=17.15.3
  66. Affected versionversion=17.15.4
  67. Affected versionversion=17.15.4d
  68. Affected versionversion=17.16.1
  69. Affected versionversion=17.17.1
  70. Affected versionversion=17.18.1
  71. Affected versionversion=17.2.1
  72. Affected versionversion=17.2.1a
  73. Affected versionversion=17.3.1
  74. Affected versionversion=17.3.2
  75. Affected versionversion=17.3.2a
  76. Affected versionversion=17.3.3
  77. Affected versionversion=17.3.4
  78. Affected versionversion=17.3.5
  79. Affected versionversion=17.3.6
  80. Affected versionversion=17.3.7
  81. Affected versionversion=17.3.8
  82. Affected versionversion=17.3.8a
  83. Affected versionversion=17.4.1
  84. Affected versionversion=17.5.1
  85. Affected versionversion=17.6.1
  86. Affected versionversion=17.6.1y
  87. Affected versionversion=17.6.2
  88. Affected versionversion=17.6.3
  89. Affected versionversion=17.6.4
  90. Affected versionversion=17.6.5
  91. Affected versionversion=17.6.5a
  92. Affected versionversion=17.6.6
  93. Affected versionversion=17.6.6a
  94. Affected versionversion=17.6.7
  95. Affected versionversion=17.6.8
  96. Affected versionversion=17.7.1
  97. Affected versionversion=17.8.1
  98. Affected versionversion=17.9.1
  99. Affected versionversion=17.9.2
  100. Affected versionversion=17.9.3
  101. Affected versionversion=17.9.4
  102. Affected versionversion=17.9.4a
  103. Affected versionversion=17.9.5
  104. Affected versionversion=17.9.6
  105. Affected versionversion=17.9.6a
  106. Affected versionversion=17.9.7
  107. Affected versionversion=17.9.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XE Softwareversion=16.10.1; version=16.10.1e; version=16.10.1s; version=16.11.1; version=16.11.1b; version=16.11.1s; version=16.12.1; version=16.12.1c; version=16.12.1s; version=16.12.2; version=16.12.2s; version=16.12.3; version=16.12.3a; version=16.12.3s; version=16.12.4; version=16.12.4a; version=16.12.5; version=16.12.5b; version=16.12.6; version=16.12.6a; version=16.12.7; version=16.12.8; version=16.6.1; version=16.6.10; version=16.6.2; version=16.6.3; version=16.6.4; version=16.6.4a; version=16.6.5; version=16.6.6; version=16.6.7; version=16.6.8; version=16.6.9; version=16.7.1; version=16.8.1; version=16.8.1a; version=16.8.1s; version=16.9.1; version=16.9.1s; version=16.9.2; version=16.9.3; version=16.9.4; version=16.9.5; version=16.9.6; version=16.9.7; version=16.9.8; version=17.10.1; version=17.10.1b; version=17.1.1; version=17.11.1; version=17.1.1s; version=17.1.1t; version=17.12.1; version=17.12.1z5; version=17.12.2; version=17.12.3; version=17.12.4; version=17.12.5; version=17.1.3; version=17.13.1; version=17.14.1; version=17.15.1; version=17.15.2; version=17.15.2b; version=17.15.3; version=17.15.4; version=17.15.4d; version=17.16.1; version=17.17.1; version=17.18.1; version=17.2.1; version=17.2.1a; version=17.3.1; version=17.3.2; version=17.3.2a; version=17.3.3; version=17.3.4; version=17.3.5; version=17.3.6; version=17.3.7; version=17.3.8; version=17.3.8a; version=17.4.1; version=17.5.1; version=17.6.1; version=17.6.1y; version=17.6.2; version=17.6.3; version=17.6.4; version=17.6.5; version=17.6.5a; version=17.6.6; version=17.6.6a; version=17.6.7; version=17.6.8; version=17.7.1; version=17.8.1; version=17.9.1; version=17.9.2; version=17.9.3; version=17.9.4; version=17.9.4a; version=17.9.5; version=17.9.6; version=17.9.6a; version=17.9.7; version=17.9.8

Published CVSS scores

8.6Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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