CVE-2019-1981 | Cisco Firepower Threat Defense Software NULL Character Obfuscation Detection Bypass Vulnerability

A vulnerability in the normalization functionality of Cisco Firepower Threat Defense Software, Cisco FirePOWER Services Software for ASA, and Cisco Firepower Management Center Software could allow an unauthenticated, remote attacker to bypass filtering protections. The vulnerability is due to insufficient normalization of a text-based payload. An attacker could exploit this vulnerability by sending traffic that contains specifically obfuscated payloads through an affected device. An exploit could allow the attacker to bypass filtering and deliver malicious payloads to protected systems that would otherwise be blocked.

Published: 2019-11-05 Last update: 2024-11-26 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2019-1981 is rated Moderate Risk (44.6/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.04%). Mandatory action: Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2019-1981

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.40% 1.04% +0.64%
2 2025-11-21 0.26% 0.40% +0.15%
3 2025-11-18 0.26%

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-1981

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.8 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
3.9 1.4 [email protected]
5.8 3.0 MEDIUM
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
10.0 2.9 [email protected]

Weakness enumeration for CVE-2019-1981

Affected software / configurations for CVE-2019-1981

Vendor Product Version Raw CPE
cisco firepower_services_software_for_asa cpe:2.3:a:cisco:firepower_services_software_for_asa:*:*:*:*:*:*:*:*
cisco firepower_threat_defense cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
cisco secure_firewall_management_center >= 2.9.12, <= 2.9.12.15 cpe:2.3:a:cisco:secure_firewall_management_center:*:*:*:*:*:*:*:*
cisco secure_firewall_management_center >= 2.9.13, <= 2.9.13.6 cpe:2.3:a:cisco:secure_firewall_management_center:*:*:*:*:*:*:*:*
cisco secure_firewall_management_center >= 2.9.14.0, <= 2.9.14.5 cpe:2.3:a:cisco:secure_firewall_management_center:*:*:*:*:*:*:*:*
cisco secure_firewall_management_center 2.9.15 cpe:2.3:a:cisco:secure_firewall_management_center:2.9.15:*:*:*:*:*:*:*
cisco secure_firewall_management_center 2.9.16 cpe:2.3:a:cisco:secure_firewall_management_center:2.9.16:*:*:*:*:*:*:*

References for CVE-2019-1981

cvelogic Threat Intelligence