CVE Intelligence
Medium

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

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.

Published Aug 5, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: cisco

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
—
No EPSS score.
Affects
Cisco
Cisco IOS XE Software
CVSS base
6.3
Medium · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Cisco Cisco IOS XE Software).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Cisco Cisco IOS XE Software version 17.4.1cversion 17.12.5dversion 17.15.4s1version 17.15.5version 17.12.1z5version 17.18.1xversion 17.12.1z6version 17.15.4d
and 144 more version 17.12.6bversion 17.9.9version 17.15.5aversion 17.18.1yversion 17.12.7aversion 17.18.3version 17.12.7bversion 17.18.3aversion 26.1.1aversion 26.2.1eaversion 17.18.1aversion 17.15.3aversion 17.15.4version 17.12.5bversion 17.15.3bversion 17.18.1zversion 17.9.7bversion 17.12.5cversion 26.1.1version 17.9.7aversion 17.15.4aversion 17.18.2version 17.18.1wversion 17.15.4bversion 17.12.6aversion 17.12.7version 17.15.4cversion 17.3.1version 17.3.1aversion 17.3.2aversion 17.3.1wversion 17.3.2version 17.4.1version 17.4.1aversion 17.3.1xversion 17.3.3version 17.5.1version 17.4.1bversion 17.3.1zversion 17.4.2version 17.3.3aversion 17.3.5version 17.3.4version 17.5.1aversion 17.6.1version 17.3.4aversion 17.6.1aversion 17.7.1version 17.6.1xversion 17.6.2version 17.3.4cversion 17.4.2aversion 17.3.4bversion 17.7.1aversion 17.8.1aversion 17.6.3aversion 17.6.3version 17.7.2version 17.7.1bversion 17.9.1wversion 17.3.5aversion 17.6.1zversion 17.8.1version 17.9.1version 17.6.4version 17.3.5bversion 17.9.1aversion 17.3.6version 17.10.1version 17.6.1z1version 17.10.1aversion 17.9.2version 17.6.5version 17.9.1xversion 17.9.1yversion 17.3.7version 17.9.2aversion 17.9.3version 17.11.1version 17.10.1bversion 17.6.6version 17.9.1x1version 17.11.1aversion 17.9.3aversion 17.12.1version 17.3.8version 17.9.4version 17.12.1wversion 17.9.1y1version 17.12.1aversion 17.9.5version 17.13.1version 17.12.1xversion 17.12.2version 17.14.1version 17.9.4aversion 17.3.8aversion 17.6.6aversion 17.6.5aversion 17.6.7version 17.15.1version 17.13.1aversion 17.12.2aversion 17.12.3version 17.12.1yversion 17.12.1zversion 17.9.5aversion 17.14.1aversion 17.9.5bversion 17.6.8version 17.12.4version 17.9.6version 17.17.1version 17.16.1version 17.15.1wversion 17.12.3aversion 17.9.5cversion 17.15.1aversion 17.12.1z1version 17.15.2version 17.15.1bversion 17.9.5dversion 17.15.1xversion 17.9.6aversion 17.12.1z2version 17.6.8aversion 17.16.1aversion 17.15.3version 17.9.7version 17.12.5version 17.15.1yversion 17.9.5eversion 17.12.4aversion 17.15.2aversion 17.15.2cversion 17.15.2bversion 17.12.1z3version 17.9.5fversion 17.12.4bversion 17.12.5aversion 17.18.1version 17.12.6version 17.12.1z4version 17.9.8
Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.3 CVSS 3.1 Medium 1.8 4.0 psirt@cisco.com via NIST National Vulnerability Database
6.3 CVSS 3.1 Medium — — cisco via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H (score shown at the top: psirt@cisco.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-126

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · cisco/cisco ios xe software
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • CVSS changed · 6.3
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Awaiting Analysis
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Aug 5, 2026 · cisco

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

1 on the record

Elsewhere on this site

Cisco
every CVE for this vendor
CWE-126
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-20308 Cisco IOS XE Software Web-Based Management Interface Vulnerability Aug 5, 2026
  • CVE-2026-20301 Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability Aug 5, 2026
  • CVE-2026-20273 Cisco IOS XE Software Security Hardening Release Aug 5, 2026
  • CVE-2026-20272 Cisco IOS XE Software Security Hardening Release Aug 5, 2026
  • CVE-2026-20271 Cisco IOS XE Software Security Hardening Release Aug 5, 2026
  • CVE-2026-20270 Cisco IOS XE Software Security Hardening Release Aug 5, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No FIRST EPSS score.
  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-20311 is "Cisco IOS XE Software Web UI Denial of Service Vulnerability", rated Medium. It affects Cisco IOS XE Software (Cisco); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.3 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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