CVE-2026-40472

Critical

Published: 23 April 2026

Published

23 April 2026

Modified

24 April 2026

KEV Added

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Patch

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CVSS Score 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L

EPSS Score 0.0005 16.1th percentile

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

Summary

CVE-2026-40472 is a critical-severity Cross-site Scripting (CWE-79) vulnerability in Osv (inferred from references). Its CVSS base score is 9.9 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 16.1th 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 SI-10 (Information Input Validation) and SI-15 (Information Output Filtering).

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-15 Information Output Filtering good match

prevent

Filters user-controlled metadata from .cabal files prior to rendering into HTML href attributes, directly preventing stored XSS payload execution in viewers' browsers.

SI-10 Information Input Validation good match

prevent

Validates metadata inputs from .cabal files to detect and reject malicious scripts before they are stored and rendered.

SI-9 Information Input Restrictions partial match

prevent

Restricts the format, length, and type of .cabal metadata inputs to limit opportunities for injecting XSS payloads.

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 →

T1059.007 JavaScript Execution

Adversaries may abuse various implementations of JavaScript for execution.

attack.mitre.org →

Why these techniques?

Stored XSS in public-facing hackage-server directly enables injection/execution of malicious JavaScript in victim browsers (T1059.007) and exploitation of the exposed web application (T1190).

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

NVD Description

In hackage-server, user-controlled metadata from .cabal files are rendered into HTML href attributes without proper sanitization, enabling stored Cross-Site Scripting (XSS) attacks.

Deeper analysisAI

CVE-2026-40472 is a stored Cross-Site Scripting (XSS) vulnerability, classified under CWE-79, affecting hackage-server. In this issue, user-controlled metadata from .cabal files is rendered into HTML href attributes without proper sanitization, enabling attackers to inject malicious scripts. The vulnerability received a CVSS v3.1 base score of 9.9 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L) and was published on 2026-04-23.

The attack requires low privileges (PR:L), allowing a registered user with the ability to submit .cabal files—such as package uploaders—to inject XSS payloads into metadata fields. These payloads persist in the server and execute in the context of other users' browsers when viewing affected package details, with no user interaction needed (UI:N). Exploitation achieves high confidentiality and integrity impacts (C:H/I:H), low availability impact (A:L), and scope change (S:C), potentially enabling session hijacking, data theft, or further compromise across the application's security context.

Mitigation details are available in the referenced advisory at https://osv.dev/vulnerability/HSEC-2026-0004.