CVE-2026-40470 | Hackage package and doc upload stored XSS vulnerability

A critical XSS vulnerability affected hackage-server and hackage.haskell.org. HTML and JavaScript files provided in source packages or via the documentation upload facility were served as-is on the main hackage.haskell.org domain. As a consequence, when a user with latent HTTP credentials browses to the package pages or documentation uploaded by a malicious package maintainer, their session can be hijacked to upload packages or documentation, amend maintainers or other package metadata, or perform any other action the user is authorised to do.

Published: 2026-04-23 Last update: 2026-04-24 Assigner: 74b3a70d-cca6-4d34-9789-e83b222ae3be Source: 74b3a70d-cca6-4d34-9789-e83b222ae3be
NVD Status：Awaiting Analysis，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40470 is rated Moderate Risk (45.2/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.05%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-40470

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-29 0.05% 0.05% +0.01%
2 2026-04-24 — 0.05% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40470

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.9 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.1 6.0 74b3a70d-cca6-4d34-9789-e83b222ae3be

Weakness enumeration for CVE-2026-40470

GitHub Security Advisory for CVE-2026-40470

GHSA-hxp4-rf8g-9mwq · Severity: critical — A critical XSS vulnerability affected hackage-server and hackage.haskell.org. HTML and...

Affected software / configurations for CVE-2026-40470

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-40470

cvelogic Threat Intelligence