VulnerabilityPublished 6 Mar 2026Updated 9 Mar 2026

CVE-2026-3610: HSC Cybersecurity Mailinspector · Cross-site Scripting

Affects HSC Cybersecurity MailinspectorSource CVE Database V5

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Public exploit available · CVSS 5.3 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

5.3Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system 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 to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 6 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, 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
HSC CybersecurityMailinspector	Affected =5.3.2-3	Fixed in–

AI-suggested

To mitigate CVE-2026-3610, organizations should immediately upgrade HSC Cybersecurity Mailinspector to version 5.4.0 or later, where the vulnerability is fully resolved. If immediate upgrade is not feasible, apply the vendor-provided hotfix to affected versions to block exploitation. Additionally, implement strict input validation and output encoding on the error_description parameter and other user-controllable inputs to prevent script injection. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in the browser context. Monitor web server logs and application behavior for unusual or suspicious requests targeting the vulnerable endpoint. Educate users about the risks of interacting with unexpected or suspicious error messages that could trigger XSS payloads. Finally, maintain an up-to-date inventory of Mailinspector deployments and ensure timely application of security patches as part of a robust vulnerability management program.

Description

A vulnerability was found in HSC Cybersecurity Mailinspector up to 5.3.2-3. Affected by this issue is some unknown functionality of the file /mailinspector/mliUserValidation.php of the component URL Handler. The manipulation of the argument error_description results in cross site scripting. The attack may be performed from remote. The exploit has been made public and could be used. Upgrading to version 5.4.0 can resolve this issue. You should upgrade the affected component. The vendor was contacted early and responded very professional: "We have already implemented the fix and made a hotfix available to affected customers, ensuring mitigation while the official release 5.4.0 has not yet been published. This allows customers to address the issue immediately, outside the regular release cycle."

Impact

The primary impact of this vulnerability is the potential for attackers to execute arbitrary scripts in the context of users’ browsers interacting with the Mailinspector interface. This can lead to session hijacking, unauthorized actions performed on behalf of the user, theft of sensitive information such as credentials or tokens, and possible redirection to malicious websites. For organizations, this could result in compromised user accounts, data breaches, and erosion of trust in the security of their email infrastructure. Since Mailinspector is a cybersecurity product used to protect email environments, exploitation could undermine the overall security posture by enabling attackers to bypass protections or gain footholds within the network. The remote and unauthenticated nature of the exploit increases the risk, especially in environments where users frequently interact with the affected component. While the vulnerability does not directly impact system availability or integrity, the confidentiality and trustworthiness of user sessions are at risk. The medium severity rating reflects these factors, but the presence of public exploit code means that attackers could weaponize this vulnerability quickly if not mitigated.

Summary

CVE-2026-3610 is a cross-site scripting vulnerability identified in HSC Cybersecurity's Mailinspector product, affecting versions up to 5.3.2-3. The vulnerability resides in the URL Handler component, specifically within the /mailinspector/mliUserValidation.php script. An attacker can manipulate the error_description parameter to inject arbitrary JavaScript code, which is then executed in the context of the victim’s browser when they interact with the affected functionality. This type of vulnerability allows attackers to bypass the same-origin policy, potentially leading to session hijacking, theft of sensitive information, or redirection to malicious sites. The attack vector is remote and does not require prior authentication, but it does require user interaction to trigger the malicious script. The vendor responded promptly by releasing a hotfix and incorporating the fix into the official 5.4.0 release, demonstrating good security practices. The CVSS 4.0 base score is 5.3 (medium severity), reflecting the moderate impact and ease of exploitation. Although no active exploitation has been reported, the availability of public exploit code increases the urgency for patching. Organizations relying on Mailinspector for email security should prioritize upgrading to the patched version or applying the hotfix to prevent potential compromise.

References

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