CVE-2026-40470
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA stored XSS vulnerability in hackage-server allowed malicious HTML and JavaScript files uploaded via source packages or documentation to be served unescaped from the main hackage.haskell.org domain. Since this domain also handles authenticated sessions, attackers could hijack user sessions by tricking authenticated maintainers into visiting crafted package pages, enabling unauthorized package uploads, metadata changes, and other privileged actions.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify if hackage-server is deployedCheck for running hackage-server processes or look for hackage-server configuration files in the deployment environmentAffected if hackage-server is not present in the environment, the system is not affected
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Determine the domain serving user-uploaded contentInspect the server configuration or visit a package documentation page on the hackage server and check the URL domain; compare it to where authentication sessions are handledAffected if User-uploaded package files and documentation are served from the same domain (hackage.haskell.org) that handles user authentication and session cookies
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Verify if authentication cookies are set on the main domainLog into the hackage server and inspect browser developer tools to see which domain sets the authentication/session cookiesAffected if Session cookies are set on the main hackage.haskell.org domain rather than a separate isolated domain
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Test for unescaped content renderingUpload or locate a test package with HTML or JavaScript in its documentation or source archive, then visit the served page and view the page source to check if special characters are rendered as-isAffected if HTML or JavaScript content from uploaded packages is served and rendered without escaping or sanitization
If hackage-server is deployed and it serves user-uploaded package content from the same domain that handles authentication (with cookies set on that domain) without sanitization, the environment is affected by this stored XSS vulnerability.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataEither sanitize all user-uploaded HTML/JS content before serving, or serve user content from a separate domain (e.g., docs.hackage.org) to prevent cookie leakage from the main authenticated domain.
- Consultation4.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40470 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40470 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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