EspoCRM up to 9.3.3 post cross site scripting

Summaryinfo

A vulnerability has been found in EspoCRM up to 9.3.3 and classified as problematic. Affected is an unknown function. Performing a manipulation of the argument post results in cross site scripting. This vulnerability was named CVE-2026-33657. The attack may be initiated remotely. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as problematic, was found in EspoCRM up to 9.3.3. This affects an unknown part. The manipulation of the argument post with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-80. The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. This is going to have an impact on integrity. The summary by CVE is:

EspoCRM is an open source customer relationship management application. Versions 9.3.3 and below have a stored HTML injection vulnerability that allows any authenticated user with standard (non-administrative) privileges to inject arbitrary HTML into system-generated email notifications by crafting malicious content in the post field of stream activity notes. The vulnerability exists because server-side Handlebars templates render the post field using unescaped triple-brace syntax, the Markdown processor preserves inline HTML by default, and the rendering pipeline explicitly skips sanitization for fields present in additionalData, creating a path where attacker-controlled HTML is accepted, stored, and rendered directly into emails without any escaping. Since the emails are sent using the system's configured SMTP identity (such as an administrative sender address), the injected content appears fully trusted to recipients, enabling phishing attacks, user tracking via embedded resources like image beacons, and UI manipulation within email content. The @mention feature further increases the impact by allowing targeted delivery of malicious emails to specific users. This issue has been fixed in version 9.3.4.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-33657 since 03/23/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 9.3.4 eliminates this vulnerability.

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Productinfo

Name

• EspoCRM

Version

• 9.3.0
• 9.3.1
• 9.3.2
• 9.3.3

License

• open-source

Website

• Product: https://github.com/espocrm/espocrm/

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