CVE-2026-33534 EspoCRM has authenticated SSRF via internal-host validation bypass using alternative IPv4 notation

Medium 4.3 Published 13 Apr 2026 Updated 14 Apr 2026

Authenticated attackers can bypass internal host validation using alternative IPv4 notations to access loopback services and read internal data.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-33534?

CVE-2026-33534 is a medium-severity server-side request forgery vulnerability in espocrm, published on 13 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

EspoCRM is an open source customer relationship management application. Versions 9.3.3 and below have an authenticated Server-Side Request Forgery (SSRF) vulnerability that allows bypassing the internal-host validation logic by using alternative IPv4 representations such as octal notation (e.g., 0177.0.0.1 instead of 127.0.0.1). This is caused by HostCheck::isNotInternalHost() function relying on PHP's filter_var(..., FILTER_VALIDATE_IP), which does not recognize alternative IP formats, causing the validation to fall through to a DNS lookup that returns no records and incorrectly treats the host as safe, however the cURL subsequently normalizes the address and connects to the loopback destination. Through the confirmed /api/v1/Attachment/fromImageUrl endpoint, an authenticated user can force the server to make requests to loopback-only services and store the fetched response as an attachment. This vulnerability is distinct from CVE-2023-46736 (which involved redirect-based SSRF) and may allow access to internal resources reachable from the application runtime. This issue has been fixed in version 9.3.4.

Weakness: CWE-918

Which versions are affected by CVE-2026-33534?

It affects 1 product.

Products include Espocrm Espocrm.

How do I fix CVE-2026-33534?

No fix has been published for CVE-2026-33534 yet. Limit exposure of the affected software until one is available.

Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.

Is CVE-2026-33534 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33534 exists.

Public exploit code: 1 Exploit-DB entry, 1 Nuclei template and 1 proofs of concept on GitHub.

Sources

Also known as GHSA-h7gx-8gwv-7g73.