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Ios Xe CVE-2021-1376

MEDIUM
Improper Verification of Cryptographic Signature (CWE-347)
2021-03-24 psirt@cisco.com
6.7
CVSS 3.1 · NVD
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Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A04:2025 - Cryptographic Failures
ASVS 5.0
V11 - Cryptography Signature verification
Impact

CVSS score of 6.7 (MEDIUM). Attack characteristics: local attack vector, low complexity, high privileges required, no user interaction not required.

Exploit ScenarioDerived

Successful exploitation could compromise the medium-severity affected system.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
No patch listed yet 0.2% exploitation probability (EPSS)

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AnalysisAI

Multiple vulnerabilities in the fast reload feature of Cisco IOS XE Software running on Cisco Catalyst 3850, Cisco Catalyst 9300, and Cisco Catalyst 9300L Series Switches could allow an. Rated medium severity (CVSS 6.7), this vulnerability is low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified under CWE-347. Multiple vulnerabilities in the fast reload feature of Cisco IOS XE Software running on Cisco Catalyst 3850, Cisco Catalyst 9300, and Cisco Catalyst 9300L Series Switches could allow an authenticated, local attacker to either execute arbitrary code on the underlying operating system, install and boot a malicious software image, or execute unsigned binaries on an affected device. These vulnerabilities are due to improper checks performed by system boot routines. To exploit these vulnerabilities, the attacker would need privileged access to the CLI of the device. A successful exploit could allow the attacker to either execute arbitrary code on the underlying operating system or execute unsigned code and bypass the image verification check part of the secure boot process. For more information about these vulnerabilities, see the Details section of this advisory. Affected products include: Cisco Ios Xe.

Severity by source

NVD PRIMARY 6.7 MEDIUM
AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionNVD

Multiple vulnerabilities in the fast reload feature of Cisco IOS XE Software running on Cisco Catalyst 3850, Cisco Catalyst 9300, and Cisco Catalyst 9300L Series Switches could allow an authenticated, local attacker to either execute arbitrary code on the underlying operating system, install and boot a malicious software image, or execute unsigned binaries on an affected device. These vulnerabilities are due to improper checks performed by system boot routines. To exploit these vulnerabilities, the attacker would need privileged access to the CLI of the device. A successful exploit could allow the attacker to either execute arbitrary code on the underlying operating system or execute unsigned code and bypass the image verification check part of the secure boot process. For more information about these vulnerabilities, see the Details section of this advisory.

Threat Intelligence Overview

EPSS Score
0.2%
Top 86% exploitable
Data Quality
2 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.2%
Patch available No
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Defer
Exploitation· derived
None
System Exposure· derived
Small
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

34
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +34
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)NVD

cpe:2.3:o:cisco:ios_xe:16.5.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.5.1a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.3:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.4:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.4a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.4s:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.5:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.6:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.7:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.6.8:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.8.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.8.1a:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.8.1s:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.9.1:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.9.1s:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.9.2:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.9.2s:*:*:*:*:*:*:*
cpe:2.3:o:cisco:ios_xe:16.9.3:*:*:*:*:*:*:*
+ 30 more

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