VulnerabilityPublished 16 Sep 2026

CVE-2026-20290: Cisco Secure Firewall Threat Defense (FTD) Software · Buffer Access with Incorrect Length Value

Affects Cisco Secure Firewall Threat Defense (FTD) SoftwareSource CVE Database V5

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Not known to be exploited · CVSS 5.8 Medium.

Data as of 31 Oct 2026, 20:20 UTC

CVSS 3.1 base score

5.8Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 23% 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:C/C:N/I:N/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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 16 Sep 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 31 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 Firewall Threat Defense (FTD) Software	Affected 7.0.0 – 7.6.4 55 affected builds	Fixed in–

AI-suggested

Users should monitor Cisco advisories for updates and apply patches once available.

Description

CVE-2026-20290 is a medium severity vulnerability in Cisco Secure Firewall Threat Defense (FTD) Software's Snort 2 Detection Engine. It involves improper validation of SSL/TLS certificates during parsing, which can be exploited by an unauthenticated remote attacker to cause the Snort 2 Detection Engine to restart unexpectedly, resulting in a denial of service (DoS).

Impact

Successful exploitation results in a denial of service condition due to unexpected restarts of the Snort 2 Detection Engine. There is no impact on confidentiality or integrity, only availability is affected.

Summary

This vulnerability arises from incomplete validation of SSL certificates in the Snort 2 Detection Engine of Cisco Secure Firewall Threat Defense (FTD) Software. An attacker can send a specially crafted SSL connection setup request that triggers the vulnerability, causing the Snort 2 Detection Engine to restart. This leads to a denial of service condition by disrupting normal detection engine operations. The vulnerability affects multiple specific versions of Cisco Secure Firewall Threat Defense (FTD) Software as enumerated.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort2-ssldos-Mw7WYX9c (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 24 Sep 2026, 05:20 UTC

Technical details

References

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