CVE-2026-4528

High

Published: 21 March 2026

Published

21 March 2026

Modified

24 April 2026

KEV Added

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Patch

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CVSS Score 7.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

EPSS Score 0.0005 16.9th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-4528 is a high-severity SSRF (CWE-918) vulnerability in Notion (inferred from references). Its CVSS base score is 7.3 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 16.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Directly addresses the flawed validateUrlSecurity function by requiring validation of URL inputs to prevent malicious inputs from enabling server-side request forgery.

AC-4 Information Flow Enforcement good match

prevent

Enforces approved information flows in the http_proxy.service, blocking unauthorized server-initiated requests to attacker-controlled URLs.

SC-7 Boundary Protection partial match

prevent

Implements boundary protections such as proxies or firewalls to monitor and restrict outbound requests from the URL Validation Handler, mitigating SSRF exploitation.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1046 Network Service Discovery Discovery

Adversaries may attempt to get a listing of services running on remote hosts and local network infrastructure devices, including those that may be vulnerable to remote software exploitation.

attack.mitre.org →

Why these techniques?

SSRF vuln in public-facing server app enables direct exploitation via T1190; SSRF responses commonly facilitate internal network/port scanning mapped to T1046.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

NVD Description

A vulnerability was determined in trueleaf ApiFlow 0.9.7. The impacted element is the function validateUrlSecurity of the file packages/server/src/service/proxy/http_proxy.service.ts of the component URL Validation Handler. This manipulation causes server-side request forgery. Remote exploitation of the attack is possible. The exploit…

has been publicly disclosed and may be utilized.

Deeper analysisAI

CVE-2026-4528 is a server-side request forgery (SSRF) vulnerability, classified under CWE-918, affecting trueleaf ApiFlow version 0.9.7. The flaw exists in the validateUrlSecurity function located in the file packages/server/src/service/proxy/http_proxy.service.ts within the URL Validation Handler component. Published on 2026-03-21, it carries a CVSS v3.1 base score of 7.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L), indicating high severity due to its network accessibility and low complexity.

Remote attackers can exploit this vulnerability without privileges or user interaction, enabling server-side request forgery. By manipulating the URL validation, attackers can trick the server into making unauthorized requests, potentially leading to limited impacts on confidentiality, integrity, and availability as per the CVSS vector.

Advisories available at VulDB (ctiid.352316, id.352316, submit.784197) and a Notion page detail the SSRF issue in ApiFlow, noting that the exploit has been publicly disclosed and may be utilized by attackers. Security practitioners should review these references for additional technical details and recommended mitigations.