CVE-2026-21393VulnerabilityPublished 4 Feb 2026

CVE-2026-21393: Six Apart Movable Type (Software Edition) · Cross-site scripting (XSS)

Affects Six Apart Movable Type (Software Edition)Source CVE Database V5

Not known to be exploited · CVSS 5.4 Medium.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.0 base score

5.4Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

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

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: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 2026-10-26.

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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC 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
Six Apart Ltd.Movable Type (Software Edition)	Affected =9.0.4 to 9.0.5 (9.0 series) =8.8.0 to 8.8.1 (8.8 series) =8.0.2 to 8.0.8 (8.0 series)	Fixed in–
Six Apart Ltd.Movable Type Advanced (Software Edition)	Affected =9.0.4 to 9.0.5 (9.0 series) =8.8.0 to 8.8.1 (8.8 series) =8.0.2 to 8.0.8 (8.0 series)	Fixed in–
Six Apart Ltd.Movable Type Premium (Software Edition)	Affected =9.0.4 (MTP 9.0 series) =2.13 and earlier (MTP 2 series)	Fixed in–
Six Apart Ltd.Movable Type Premium (Advanced Edition) (Software Edition)	Affected =9.0.4 (MTP 9.0 series) =2.13 and earlier (MTP 2 series)	Fixed in–
Six Apart Ltd.Movable Type (Cloud Edition)	Affected =9.0.5 (9 series) =8.8.1 (8 series)	Fixed in–
Six Apart Ltd.Movable Type Premium (Cloud Edition)	Affected =9.0.5 (9 series) =2.12 (MTP 2 series)	Fixed in–

AI-suggested

Organizations should immediately identify and inventory all instances of Movable Type in use, including EOL versions 7 and 8.4, and prioritize upgrading to the latest patched versions beyond 9.0.5 where the vulnerability is fixed. If patching is not immediately possible, implement web application firewall (WAF) rules to detect and block suspicious input patterns targeting the Edit Comment functionality. Enforce strict input validation and output encoding on all user-generated content to prevent script injection. Limit privileges for users who can submit comments and monitor logs for unusual comment submissions or user activity. Educate users about the risks of interacting with untrusted content, especially within authenticated sessions. Regularly review and update security policies related to web application security and user access controls. Conduct security testing and code reviews focused on XSS vulnerabilities in all web-facing applications. Finally, consider deploying Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers.

Description

CVE-2026-21393 is a stored cross-site scripting (XSS) vulnerability affecting Six Apart Ltd. 's Movable Type (Software Edition) versions 8.0.2 to 8.0.8, 8.8.0 to 8.8.1, and 9.

Impact

For European organizations using Movable Type for blogging or content management, this vulnerability poses a risk of client-side script execution leading to session hijacking, theft of sensitive information, or unauthorized actions performed with user privileges. This can compromise user accounts, leak confidential information, and damage organizational reputation. Since the vulnerability requires authenticated users to interact with malicious content, internal users or administrators are at risk, potentially leading to privilege escalation or lateral movement within the organization. Public-facing websites are particularly vulnerable to targeted attacks by threat actors aiming to exploit this flaw to gain footholds or steal credentials. The impact is medium severity but can escalate if combined with other vulnerabilities or social engineering tactics. Organizations in sectors with strict data protection regulations, such as finance, healthcare, and government, may face compliance risks if user data is compromised.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Feb 2026, 12:05 UTC

Technical details

References

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