CVE Intelligence
High

CVE-2026-20004 — A vulnerability in the TLS library of Cisco IOS XE Software could allow an…

A vulnerability in the TLS library of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to exhaust the available memory of an affected device. This vulnerability is due to improper management of memory resources during TLS connection setup. An attacker could exploit this vulnerability by repeatedly triggering the conditions that cause the memory increase. This could be done in a variety of ways, such as by repeatedly attempting Extensible Authentication Protocol (EAP) authentication when local EAP is enabled on an affected device or by using a machine-in-the-middle attack and resetting TLS connections between the affected device and other devices. A successful exploit could allow the attacker to exhaust the available memory on an affected device, resulting in an unexpected reload and a denial of service (DoS) condition.

Published Mar 25, 2026 · Updated Oct 13, 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
  • EPSS 0.2% (30-day exploitation probability)+1
  • Technical severity (high)+6

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
0.18%
ahead of 7% of scored CVEs · Oct 14, 2026
Affects
Cisco
Cisco IOS XE Software and 1 more
CVSS base
7.4
High · 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, Cisco Ios Xe).
  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 17.15.1yversion 17.16.1version 17.16.1aversion 16.12.12version 16.12.13version 16.12.14version 16.12.15version 17.1.1
and 172 more version 17.1.1aversion 17.1.1sversion 17.1.1tversion 17.1.3version 17.2.1version 17.2.1rversion 17.2.1aversion 17.2.1vversion 17.2.2version 17.2.3version 17.3.1version 17.3.2version 17.3.3version 17.3.1aversion 17.3.1wversion 17.3.2aversion 17.3.1xversion 17.3.1zversion 17.3.4version 17.3.5version 17.3.4aversion 17.3.6version 17.3.4bversion 17.3.4cversion 17.3.5aversion 17.3.5bversion 17.3.7version 17.3.8version 17.3.8aversion 17.4.1version 17.4.2version 17.4.1aversion 17.4.1bversion 17.4.2aversion 17.5.1version 17.5.1aversion 17.6.1version 17.6.2version 17.6.1wversion 17.6.1aversion 17.6.1xversion 17.6.3version 17.6.1yversion 17.6.1zversion 17.6.3aversion 17.6.4version 17.6.1z1version 17.6.5version 17.6.6version 17.6.6aversion 17.6.5aversion 17.6.7version 17.6.8version 17.6.8aversion 17.7.1version 17.7.1aversion 17.7.1bversion 17.7.2version 17.10.1version 17.10.1aversion 17.10.1bversion 17.8.1version 17.8.1aversion 17.9.1version 17.9.1wversion 17.9.2version 17.9.1aversion 17.9.1xversion 17.9.1yversion 17.9.3version 17.9.2aversion 17.9.1x1version 17.9.3aversion 17.9.4version 17.9.1y1version 17.9.5version 17.9.4aversion 17.9.5aversion 17.9.5bversion 17.9.6version 17.9.6aversion 17.9.5eversion 17.9.5fversion 17.11.1version 17.11.1aversion 17.12.1version 17.12.1wversion 17.12.1aversion 17.12.1xversion 17.12.2version 17.12.3version 17.12.2aversion 17.12.1yversion 17.12.1zversion 17.12.4version 17.12.3aversion 17.12.1z1version 17.12.1z2version 17.12.4aversion 17.12.4bversion 17.12.1z3version 17.12.1z4version 17.12.1z5version 17.12.1z6version 17.13.1version 17.13.1aversion 17.14.1version 17.14.1aversion 17.15.1version 17.15.1wversion 17.15.1aversion 17.15.1bversion 17.15.1xversion 17.15.1zversion 16.9.1version 16.9.2version 16.9.1aversion 16.9.1bversion 16.9.1sversion 16.9.3version 16.9.4version 16.9.3aversion 16.9.5version 16.9.5fversion 16.9.6version 16.9.7version 16.9.8version 16.10.1version 16.10.1aversion 16.10.1bversion 16.10.1sversion 16.10.1cversion 16.10.1eversion 16.10.1dversion 16.10.2version 16.10.1fversion 16.10.1gversion 16.10.3version 16.11.1version 16.11.1aversion 16.11.1bversion 16.11.2version 16.11.1sversion 16.12.1version 16.12.1sversion 16.12.1aversion 16.12.1cversion 16.12.1wversion 16.12.2version 16.12.1yversion 16.12.2aversion 16.12.3version 16.12.8version 16.12.2sversion 16.12.1xversion 16.12.1tversion 16.12.4version 16.12.3sversion 16.12.3aversion 16.12.4aversion 16.12.5version 16.12.6version 16.12.1z1version 16.12.5aversion 16.12.5bversion 16.12.1z2version 16.12.6aversion 16.12.7version 16.12.9version 16.12.10version 16.12.10aversion 16.12.11
Vulnerable CVE Program (cve.org) e CISA ADP
Cisco Ios Xe version 17.7.1bversion 17.7.2version 17.8.1version 17.8.1aversion 17.9.1version 17.9.1aversion 17.9.1wversion 17.9.1x
and 112 more version 17.9.1x1version 17.9.1yversion 17.9.1y1version 17.9.2version 17.9.2aversion 17.9.3version 17.9.3aversion 17.9.4version 17.9.4aversion 17.9.5version 17.9.5aversion 17.9.5bversion 17.9.5eversion 17.9.5fversion 17.9.6version 17.9.6aversion 17.10.1version 17.10.1aversion 17.10.1bversion 17.11.1version 17.11.1aversion 17.12.1version 17.12.1aversion 17.12.1wversion 17.12.1xversion 17.12.1yversion 17.12.1zversion 17.12.1z1version 17.12.1z2version 17.12.1z3version 17.12.1z4version 17.12.1z5version 17.12.1z6version 17.12.2version 17.12.2aversion 17.12.3version 17.12.3aversion 17.12.4version 17.12.4aversion 17.12.4bversion 17.13.1version 17.13.1aversion 17.14.1version 17.14.1aversion 17.15.1version 17.15.1aversion 17.15.1bversion 17.15.1wversion 17.15.1xversion 17.15.1yversion 17.15.1zversion 17.16.1version 17.16.1aversion 16.9.1version 16.9.1aversion 16.9.1bversion 16.9.1sversion 16.9.2version 16.9.3version 16.9.3aversion 16.9.4version 16.9.5version 16.9.5fversion 16.9.6version 16.9.7version 16.9.8version 16.10.1version 16.10.1aversion 16.10.1bversion 16.10.1cversion 16.10.1dversion 16.10.1eversion 16.10.1fversion 16.10.1gversion 16.10.1sversion 16.10.2version 16.10.3version 16.11.1version 16.11.1aversion 16.11.1bversion 16.11.1sversion 16.11.2version 16.12.1version 16.12.1aversion 16.12.1cversion 16.12.1sversion 16.12.1tversion 16.12.1wversion 16.12.1xversion 16.12.1yversion 16.12.1z1version 16.12.1z2version 16.12.2version 16.12.2aversion 16.12.2sversion 16.12.3version 16.12.3aversion 16.12.3sversion 16.12.4version 16.12.4aversion 16.12.5version 16.12.5aversion 16.12.5bversion 16.12.6version 16.12.6aversion 16.12.7version 16.12.8version 16.12.9version 16.12.10version 16.12.10aversion 16.12.11version 16.12.12
Vulnerable NIST National Vulnerability Database

Attack characteristics

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

Attack vector
Adjacent
Attack complexity
Low
Privileges required
None
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
7.4 CVSS 3.1 High 2.8 4.0 psirt@cisco.com via NIST National Vulnerability Database
7.4 CVSS 3.1 High — — cisco via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:A/AC:L/PR:N/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-771

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.18%

Detection

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

  • Not enough vector or weakness data: use the affected application’s logs as a starting point.
application logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · cisco/cisco ios xe software
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • CVSS changed · 7.4
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Mar 25, 2026 · cisco

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

Elsewhere on this site

Cisco
every CVE for this vendor
CWE-771
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-20115 Cleartext Transmission of Sensitive Information in Cisco Cisco IOS XE Software Mar 25, 2026
  • CVE-2026-20114 A vulnerability in the Lobby Ambassador web-based management API of Cisco IOS XE… Mar 25, 2026
  • CVE-2026-20125 A vulnerability in the HTTP Server feature of Cisco IOS Software and Cisco IOS XE… Mar 25, 2026
  • CVE-2026-20113 A vulnerability in the web-based Cisco IOx application hosting environment management… Mar 25, 2026
  • CVE-2026-20112 Cross-site Scripting (XSS) in Cisco Cisco IOS XE Software Mar 25, 2026
  • CVE-2026-20104 A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200… Mar 25, 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 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-2026-20004 is "A vulnerability in the TLS library of Cisco IOS XE Software could allow an…", rated High. 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 7.4 describes technical severity. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. 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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