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

Quick assessment

Affected
espocrm espocrm
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

EspoCRM是EspoCRM开源的一套开源的基于Web的客户关系管理系统（CRM）。该系统提供销售自动化、社区和客户支持等功能。 EspoCRM 9.3.3及之前版本存在代码问题漏洞，该漏洞源于HostCheck::isNotInternalHost函数依赖的PHP filter_var函数无法识别替代IPv4表示法，可能导致服务端请求伪造攻击。

CVSS 4.3 · Medium EPSS 1.68% · P76

Public Exploits 2

ExploitDB · 1 EDB-52583 [webapps]
Nuclei · 1 CVE-2026-33534.yaml [template]
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I. Basic Information for CVE-2026-33534

Vulnerability Information
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Vulnerability Title
EspoCRM has authenticated SSRF via internal-host validation bypass using alternative IPv4 notation
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
EspoCRM 代码问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
EspoCRM是EspoCRM开源的一套开源的基于Web的客户关系管理系统（CRM）。该系统提供销售自动化、社区和客户支持等功能。 EspoCRM 9.3.3及之前版本存在代码问题漏洞，该漏洞源于HostCheck::isNotInternalHost函数依赖的PHP filter_var函数无法识别替代IPv4表示法，可能导致服务端请求伪造攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
espocrm espocrm < 9.3.4 -

II. Public POCs for CVE-2026-33534

# POC Description Source Link Shenlong Link
1 EspoCRM <= 9.3.3 contains an authenticated server-side request forgery caused by improper internal-host validation using alternative IPv4 formats in HostCheck::isNotInternalHost(), letting authenticated users access internal resources via /api/v1/Attachment/fromImageUrl endpoint. https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-33534.yaml POC Details
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III. Intelligence Information for CVE-2026-33534

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Vendor Advisories for CVE-2026-33534 (1)

Same Patch Batch · espocrm · 2026-04-13 · 4 CVEs total

CVE-2026-33740 5.4 MEDIUM EspoCRM: Email importEml can import and delete another user's attachment by raw fileId
CVE-2026-33657 4.6 MEDIUM EspoCRM: Stored HTML injection in email notifications about stream notes via unescaped pos
CVE-2026-33659 3.5 LOW EspoCRM: SSRF via DNS Rebinding in Attachment fromImageUrl Endpoint Allows Internal Networ

IV. Related Vulnerabilities

Same product: espocrm
Same vendor: espocrm
Same weakness: CWE-918

V. Comments for CVE-2026-33534

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