CVE-2026-33657 EspoCRM: Stored HTML injection in email notifications about stream notes via unescaped post field
Authenticated users can inject HTML into email notifications via stream notes, enabling phishing and tracking against recipients.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-33657?
CVE-2026-33657 is a medium-severity cross-site scripting vulnerability in espocrm, published on 13 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-33657?
It affects 1 product.
Products include Espocrm Espocrm.
How do I fix CVE-2026-33657?
No fix has been published for CVE-2026-33657 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-33657 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33657 exists.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in espocrm
Sources
Also known as GHSA-8prm-r5j9-j574.