CVE-2026-20271Network attack vector

Unauthenticated service interruption via undisclosed control-flow flaws

Published Aug 5, 2026 · Updated Aug 5, 2026

Insufficient control-flow management in Cisco IOS XE Software allows remote attackers to interrupt device services over the network. Cisco has not disclosed the affected components or which operations permit infinite loops, uncontrolled recursion, or race conditions. Autonomous and controller modes are affected regardless of configuration; exploitation requires no privileges or user interaction and has only availability impact.

CVSS severity8.6
High
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient control-flow management in Cisco IOS XE Software allows remote attackers to interrupt device services over the network. Cisco has not disclosed the affected components or which operations permit infinite loops, uncontrolled recursion, or race conditions. Autonomous and controller modes are affected regardless of configuration; exploitation requires no privileges or user interaction and has only availability impact.

The record

CVE
CVE-2026-20271
Published
Aug 5, 2026
Updated
Aug 5, 2026
Vendor
ClamAV
Product
Cisco IOS XE Software
Classifications
CWE-691, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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=16.10.1a
  3. Affected versionversion=16.10.1b
  4. Affected versionversion=16.10.1c
  5. Affected versionversion=16.10.1d
  6. Affected versionversion=16.10.1e
  7. Affected versionversion=16.10.1f
  8. Affected versionversion=16.10.1g
  9. Affected versionversion=16.10.1s
  10. Affected versionversion=16.10.2
  11. Affected versionversion=16.10.3
  12. Affected versionversion=16.11.1
  13. Affected versionversion=16.11.1a
  14. Affected versionversion=16.11.1b
  15. Affected versionversion=16.11.1c
  16. Affected versionversion=16.11.1s
  17. Affected versionversion=16.11.2
  18. Affected versionversion=16.12.1
  19. Affected versionversion=16.12.10
  20. Affected versionversion=16.12.10a
  21. Affected versionversion=16.12.11
  22. Affected versionversion=16.12.12
  23. Affected versionversion=16.12.13
  24. Affected versionversion=16.12.14
  25. Affected versionversion=16.12.15
  26. Affected versionversion=16.12.16
  27. Affected versionversion=16.12.1a
  28. Affected versionversion=16.12.1c
  29. Affected versionversion=16.12.1s
  30. Affected versionversion=16.12.1t
  31. Affected versionversion=16.12.1w
  32. Affected versionversion=16.12.1x
  33. Affected versionversion=16.12.1y
  34. Affected versionversion=16.12.1z
  35. Affected versionversion=16.12.1z1
  36. Affected versionversion=16.12.1z2
  37. Affected versionversion=16.12.2
  38. Affected versionversion=16.12.2a
  39. Affected versionversion=16.12.2s
  40. Affected versionversion=16.12.2t
  41. Affected versionversion=16.12.3
  42. Affected versionversion=16.12.3a
  43. Affected versionversion=16.12.3s
  44. Affected versionversion=16.12.4
  45. Affected versionversion=16.12.4a
  46. Affected versionversion=16.12.5
  47. Affected versionversion=16.12.5a
  48. Affected versionversion=16.12.5b
  49. Affected versionversion=16.12.6
  50. Affected versionversion=16.12.6a
  51. Affected versionversion=16.12.7
  52. Affected versionversion=16.12.8
  53. Affected versionversion=16.12.9
  54. Affected versionversion=16.6.10
  55. Affected versionversion=16.6.2
  56. Affected versionversion=16.6.3
  57. Affected versionversion=16.6.4
  58. Affected versionversion=16.6.4a
  59. Affected versionversion=16.6.4s
  60. Affected versionversion=16.6.5
  61. Affected versionversion=16.6.5a
  62. Affected versionversion=16.6.5b
  63. Affected versionversion=16.6.6
  64. Affected versionversion=16.6.7
  65. Affected versionversion=16.6.7a
  66. Affected versionversion=16.6.8
  67. Affected versionversion=16.6.9
  68. Affected versionversion=16.7.1
  69. Affected versionversion=16.7.1a
  70. Affected versionversion=16.7.1b
  71. Affected versionversion=16.7.2
  72. Affected versionversion=16.7.3
  73. Affected versionversion=16.7.4
  74. Affected versionversion=16.8.1
  75. Affected versionversion=16.8.1a
  76. Affected versionversion=16.8.1b
  77. Affected versionversion=16.8.1c
  78. Affected versionversion=16.8.1d
  79. Affected versionversion=16.8.1e
  80. Affected versionversion=16.8.1s
  81. Affected versionversion=16.8.2
  82. Affected versionversion=16.8.3
  83. Affected versionversion=16.9.1
  84. Affected versionversion=16.9.1a
  85. Affected versionversion=16.9.1b
  86. Affected versionversion=16.9.1c
  87. Affected versionversion=16.9.1d
  88. Affected versionversion=16.9.1s
  89. Affected versionversion=16.9.2
  90. Affected versionversion=16.9.2a
  91. Affected versionversion=16.9.2s
  92. Affected versionversion=16.9.3
  93. Affected versionversion=16.9.3a
  94. Affected versionversion=16.9.3h
  95. Affected versionversion=16.9.3s
  96. Affected versionversion=16.9.4
  97. Affected versionversion=16.9.4c
  98. Affected versionversion=16.9.5
  99. Affected versionversion=16.9.5f
  100. Affected versionversion=16.9.6
  101. Affected versionversion=16.9.7
  102. Affected versionversion=16.9.8
  103. Affected versionversion=16.9.8a
  104. Affected versionversion=16.9.8b
  105. Affected versionversion=17.10.1
  106. Affected versionversion=17.10.1a
  107. Affected versionversion=17.10.1b
  108. Affected versionversion=17.1.1
  109. Affected versionversion=17.11.1
  110. Affected versionversion=17.11.1a
  111. Affected versionversion=17.1.1a
  112. Affected versionversion=17.1.1s
  113. Affected versionversion=17.1.1t
  114. Affected versionversion=17.1.2
  115. Affected versionversion=17.12.1
  116. Affected versionversion=17.12.1a
  117. Affected versionversion=17.12.1w
  118. Affected versionversion=17.12.1x
  119. Affected versionversion=17.12.1y
  120. Affected versionversion=17.12.1z
  121. Affected versionversion=17.12.1z1
  122. Affected versionversion=17.12.1z2
  123. Affected versionversion=17.12.1z3
  124. Affected versionversion=17.12.1z4
  125. Affected versionversion=17.12.1z5
  126. Affected versionversion=17.12.1z6
  127. Affected versionversion=17.12.2
  128. Affected versionversion=17.12.2a
  129. Affected versionversion=17.12.3
  130. Affected versionversion=17.12.3a
  131. Affected versionversion=17.12.4
  132. Affected versionversion=17.12.4a
  133. Affected versionversion=17.12.4b
  134. Affected versionversion=17.12.5
  135. Affected versionversion=17.12.5a
  136. Affected versionversion=17.12.5b
  137. Affected versionversion=17.12.5c
  138. Affected versionversion=17.12.5d
  139. Affected versionversion=17.12.6
  140. Affected versionversion=17.12.6a
  141. Affected versionversion=17.12.6b
  142. Affected versionversion=17.12.7
  143. Affected versionversion=17.12.7a
  144. Affected versionversion=17.12.7b
  145. Affected versionversion=17.1.3
  146. Affected versionversion=17.13.1
  147. Affected versionversion=17.13.1a
  148. Affected versionversion=17.14.1
  149. Affected versionversion=17.14.1a
  150. Affected versionversion=17.15.1
  151. Affected versionversion=17.15.1a
  152. Affected versionversion=17.15.1b
  153. Affected versionversion=17.15.1w
  154. Affected versionversion=17.15.1x
  155. Affected versionversion=17.15.1y
  156. Affected versionversion=17.15.2
  157. Affected versionversion=17.15.2a
  158. Affected versionversion=17.15.2b
  159. Affected versionversion=17.15.2c
  160. Affected versionversion=17.15.3
  161. Affected versionversion=17.15.3a
  162. Affected versionversion=17.15.3b
  163. Affected versionversion=17.15.4
  164. Affected versionversion=17.15.4a
  165. Affected versionversion=17.15.4b
  166. Affected versionversion=17.15.4c
  167. Affected versionversion=17.15.4d
  168. Affected versionversion=17.15.4s1
  169. Affected versionversion=17.15.5
  170. Affected versionversion=17.15.5a
  171. Affected versionversion=17.15.7
  172. Affected versionversion=17.16.1
  173. Affected versionversion=17.16.1a
  174. Affected versionversion=17.17.1
  175. Affected versionversion=17.18.1
  176. Affected versionversion=17.18.1a
  177. Affected versionversion=17.18.1w
  178. Affected versionversion=17.18.1x
  179. Affected versionversion=17.18.1y
  180. Affected versionversion=17.18.1z
  181. Affected versionversion=17.18.2
  182. Affected versionversion=17.18.3
  183. Affected versionversion=17.18.3a
  184. Affected versionversion=17.2.1
  185. Affected versionversion=17.2.1a
  186. Affected versionversion=17.2.1r
  187. Affected versionversion=17.2.1v
  188. Affected versionversion=17.2.2
  189. Affected versionversion=17.2.3
  190. Affected versionversion=17.3.1
  191. Affected versionversion=17.3.1a
  192. Affected versionversion=17.3.1w
  193. Affected versionversion=17.3.1x
  194. Affected versionversion=17.3.1z
  195. Affected versionversion=17.3.2
  196. Affected versionversion=17.3.2a
  197. Affected versionversion=17.3.3
  198. Affected versionversion=17.3.3a
  199. Affected versionversion=17.3.4
  200. Affected versionversion=17.3.4a
  201. Affected versionversion=17.3.4b
  202. Affected versionversion=17.3.4c
  203. Affected versionversion=17.3.5
  204. Affected versionversion=17.3.5a
  205. Affected versionversion=17.3.5b
  206. Affected versionversion=17.3.6
  207. Affected versionversion=17.3.7
  208. Affected versionversion=17.3.8
  209. Affected versionversion=17.3.8a
  210. Affected versionversion=17.4.1
  211. Affected versionversion=17.4.1a
  212. Affected versionversion=17.4.1b
  213. Affected versionversion=17.4.1c
  214. Affected versionversion=17.4.2
  215. Affected versionversion=17.4.2a
  216. Affected versionversion=17.5.1
  217. Affected versionversion=17.5.1a
  218. Affected versionversion=17.6.1
  219. Affected versionversion=17.6.1a
  220. Affected versionversion=17.6.1x
  221. Affected versionversion=17.6.1z
  222. Affected versionversion=17.6.1z1
  223. Affected versionversion=17.6.2
  224. Affected versionversion=17.6.3
  225. Affected versionversion=17.6.3a
  226. Affected versionversion=17.6.4
  227. Affected versionversion=17.6.5
  228. Affected versionversion=17.6.5a
  229. Affected versionversion=17.6.6
  230. Affected versionversion=17.6.6a
  231. Affected versionversion=17.6.7
  232. Affected versionversion=17.6.8
  233. Affected versionversion=17.6.8a
  234. Affected versionversion=17.7.1
  235. Affected versionversion=17.7.1a
  236. Affected versionversion=17.7.1b
  237. Affected versionversion=17.7.2
  238. Affected versionversion=17.8.1
  239. Affected versionversion=17.8.1a
  240. Affected versionversion=17.9.1
  241. Affected versionversion=17.9.1a
  242. Affected versionversion=17.9.1w
  243. Affected versionversion=17.9.1x
  244. Affected versionversion=17.9.1x1
  245. Affected versionversion=17.9.1y
  246. Affected versionversion=17.9.1y1
  247. Affected versionversion=17.9.2
  248. Affected versionversion=17.9.2a
  249. Affected versionversion=17.9.3
  250. Affected versionversion=17.9.3a
  251. Affected versionversion=17.9.4
  252. Affected versionversion=17.9.4a
  253. Affected versionversion=17.9.5
  254. Affected versionversion=17.9.5a
  255. Affected versionversion=17.9.5b
  256. Affected versionversion=17.9.5c
  257. Affected versionversion=17.9.5d
  258. Affected versionversion=17.9.5e
  259. Affected versionversion=17.9.5f
  260. Affected versionversion=17.9.6
  261. Affected versionversion=17.9.6a
  262. Affected versionversion=17.9.7
  263. Affected versionversion=17.9.7a
  264. Affected versionversion=17.9.7b
  265. Affected versionversion=17.9.8
  266. Affected versionversion=17.9.9
  267. Affected versionversion=26.1.1
  268. Affected versionversion=26.1.1a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco IOS XE Softwareversion=16.10.1; version=16.10.1a; version=16.10.1b; version=16.10.1c; version=16.10.1d; version=16.10.1e; version=16.10.1f; version=16.10.1g; version=16.10.1s; version=16.10.2; version=16.10.3; version=16.11.1; version=16.11.1a; version=16.11.1b; version=16.11.1c; version=16.11.1s; version=16.11.2; version=16.12.1; version=16.12.10; version=16.12.10a; version=16.12.11; version=16.12.12; version=16.12.13; version=16.12.14; version=16.12.15; version=16.12.16; version=16.12.1a; version=16.12.1c; version=16.12.1s; version=16.12.1t; version=16.12.1w; version=16.12.1x; version=16.12.1y; version=16.12.1z; version=16.12.1z1; version=16.12.1z2; version=16.12.2; version=16.12.2a; version=16.12.2s; version=16.12.2t; 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=16.12.5a; version=16.12.5b; version=16.12.6; version=16.12.6a; version=16.12.7; version=16.12.8; version=16.12.9; version=16.6.10; version=16.6.2; version=16.6.3; version=16.6.4; version=16.6.4a; version=16.6.4s; version=16.6.5; version=16.6.5a; version=16.6.5b; version=16.6.6; version=16.6.7; version=16.6.7a; version=16.6.8; version=16.6.9; version=16.7.1; version=16.7.1a; version=16.7.1b; version=16.7.2; version=16.7.3; version=16.7.4; version=16.8.1; version=16.8.1a; version=16.8.1b; version=16.8.1c; version=16.8.1d; version=16.8.1e; version=16.8.1s; version=16.8.2; version=16.8.3; version=16.9.1; version=16.9.1a; version=16.9.1b; version=16.9.1c; version=16.9.1d; version=16.9.1s; version=16.9.2; version=16.9.2a; version=16.9.2s; version=16.9.3; version=16.9.3a; version=16.9.3h; version=16.9.3s; version=16.9.4; version=16.9.4c; version=16.9.5; version=16.9.5f; version=16.9.6; version=16.9.7; version=16.9.8; version=16.9.8a; version=16.9.8b; version=17.10.1; version=17.10.1a; version=17.10.1b; version=17.1.1; version=17.11.1; version=17.11.1a; version=17.1.1a; version=17.1.1s; version=17.1.1t; version=17.1.2; version=17.12.1; version=17.12.1a; version=17.12.1w; version=17.12.1x; version=17.12.1y; version=17.12.1z; version=17.12.1z1; version=17.12.1z2; version=17.12.1z3; version=17.12.1z4; version=17.12.1z5; version=17.12.1z6; version=17.12.2; version=17.12.2a; version=17.12.3; version=17.12.3a; version=17.12.4; version=17.12.4a; version=17.12.4b; version=17.12.5; version=17.12.5a; version=17.12.5b; version=17.12.5c; version=17.12.5d; version=17.12.6; version=17.12.6a; version=17.12.6b; version=17.12.7; version=17.12.7a; version=17.12.7b; version=17.1.3; version=17.13.1; version=17.13.1a; version=17.14.1; version=17.14.1a; version=17.15.1; version=17.15.1a; version=17.15.1b; version=17.15.1w; version=17.15.1x; version=17.15.1y; version=17.15.2; version=17.15.2a; version=17.15.2b; version=17.15.2c; version=17.15.3; version=17.15.3a; version=17.15.3b; version=17.15.4; version=17.15.4a; version=17.15.4b; version=17.15.4c; version=17.15.4d; version=17.15.4s1; version=17.15.5; version=17.15.5a; version=17.15.7; version=17.16.1; version=17.16.1a; version=17.17.1; version=17.18.1; version=17.18.1a; version=17.18.1w; version=17.18.1x; version=17.18.1y; version=17.18.1z; version=17.18.2; version=17.18.3; version=17.18.3a; version=17.2.1; version=17.2.1a; version=17.2.1r; version=17.2.1v; version=17.2.2; version=17.2.3; version=17.3.1; version=17.3.1a; version=17.3.1w; version=17.3.1x; version=17.3.1z; version=17.3.2; version=17.3.2a; version=17.3.3; version=17.3.3a; version=17.3.4; version=17.3.4a; version=17.3.4b; version=17.3.4c; version=17.3.5; version=17.3.5a; version=17.3.5b; version=17.3.6; version=17.3.7; version=17.3.8; version=17.3.8a; version=17.4.1; version=17.4.1a; version=17.4.1b; version=17.4.1c; version=17.4.2; version=17.4.2a; version=17.5.1; version=17.5.1a; version=17.6.1; version=17.6.1a; version=17.6.1x; version=17.6.1z; version=17.6.1z1; version=17.6.2; version=17.6.3; version=17.6.3a; 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=17.6.8a; version=17.7.1; version=17.7.1a; version=17.7.1b; version=17.7.2; version=17.8.1; version=17.8.1a; version=17.9.1; version=17.9.1a; version=17.9.1w; version=17.9.1x; version=17.9.1x1; version=17.9.1y; version=17.9.1y1; version=17.9.2; version=17.9.2a; version=17.9.3; version=17.9.3a; version=17.9.4; version=17.9.4a; version=17.9.5; version=17.9.5a; version=17.9.5b; version=17.9.5c; version=17.9.5d; version=17.9.5e; version=17.9.5f; version=17.9.6; version=17.9.6a; version=17.9.7; version=17.9.7a; version=17.9.7b; version=17.9.8; version=17.9.9; version=26.1.1; version=26.1.1a

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

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-691Insufficient Control Flow Management
T1499Endpoint Denial of Service

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

See the directory against your own environment.

Your stack

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