VulnerabilityPublished 4 Mar 2026

CVE-2026-20031: Cisco Secure Endpoint · Uncaught Exception

Affects Cisco Secure EndpointSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 38% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CiscoCisco Secure Endpoint	Affected 1.1.0 – 8.4.5.30483 162 affected builds	Fixed in–

AI-suggested

Monitor Cisco's official security advisories and apply patches or updates promptly once released to address CVE-2026-20031.
Implement file submission controls to restrict or validate files scanned by Cisco Secure Endpoint, reducing exposure to crafted malicious HTML files.
Employ network segmentation and strict access controls to limit the ability of unauthenticated users to submit files for scanning.
Enable detailed logging and monitoring of the scanning process to detect abnormal terminations or failures indicative of exploitation attempts.
Consider deploying additional layered endpoint security solutions to provide defense-in-depth in case of temporary scanning failures.
Conduct regular security assessments and penetration testing to identify potential exploitation vectors related to file scanning processes.
Educate security operations teams about this vulnerability to ensure rapid incident response if scanning disruptions are detected.
If possible, configure ClamAV or Cisco Secure Endpoint to handle UTF-8 parsing errors more gracefully or apply custom input validation filters to mitigate malformed inputs.
Maintain up-to-date backups and incident response plans to recover quickly from potential malware infections resulting from scanning downtime.

Description

A vulnerability in the HTML Cascading Style Sheets (CSS) module of ClamAV could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper error handling when splitting UTF-8 strings. An attacker could exploit this vulnerability by submitting a crafted HTML file to be scanned by ClamAV on an affected device. A successful exploit could allow the attacker to terminate the scanning process.

Impact

The primary impact of CVE-2026-20031 is a denial of service condition affecting Cisco Secure Endpoint's malware scanning capability. By causing the scanning process to terminate, attackers can temporarily disable endpoint protection, increasing the risk of undetected malware infections. This can lead to potential downstream impacts such as lateral movement, data exfiltration, or ransomware attacks if malicious files bypass detection during the downtime. Since the vulnerability does not affect confidentiality or integrity directly, the risk is confined to availability of security services. However, given Cisco Secure Endpoint's widespread use in enterprise environments for endpoint protection, the vulnerability could affect a large number of organizations globally. Critical infrastructure, financial institutions, healthcare providers, and government agencies relying on Cisco Secure Endpoint may face increased exposure to malware threats if this vulnerability is exploited. The ease of exploitation without authentication or user interaction further elevates the risk. Although no active exploitation is known, the vulnerability represents a significant operational risk until remediated.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-clamav-css-Fn4QSZ (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Mar 2026, 19:45 UTC

Technical details

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