CVE-2026-66882
Received Received - Intake

Reflected XSS in AshAuthentication

Publication date: 2026-08-25

Last updated on: 2026-08-25

Assigner: EEF

Description
Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in team-alembic AshAuthentication allows reflected cross-site scripting via the confirmation and magic link interaction forms. When a strategy is configured with require_interaction? set to true, AshAuthentication serves an intermediate HTML page asking the user to confirm the action by submitting a form. Both such pages embed a request parameter directly into a hidden input's value attribute without HTML escaping: lib/ash_authentication/add_ons/confirmation/confirmation_form.html.eex interpolates the confirm parameter, and lib/ash_authentication/strategies/magic_link/sign_in_form.html.eex interpolates the magic link token parameter. These templates are compiled with EEx.function_from_file/3 using plain <%= %> expressions, which perform no escaping, so the parameter is reflected verbatim. Neither accept handler validates the value before rendering it. AshAuthentication.AddOn.Confirmation.Plug.accept/2 only checks that a confirm key is present, and AshAuthentication.Strategy.MagicLink.Plug.accept/2 reads the parameter directly, so no token signature is verified at this stage and arbitrary attacker-supplied text reaches the template. An unauthenticated attacker can therefore craft a URL whose parameter terminates the attribute and injects markup, for example a quote followed by a <script> element. Because the accept phase is served over GET, loading the crafted link is sufficient; no form submission or prior authentication is required. The injected script executes in the origin of the application embedding AshAuthentication, giving it access to that origin's cookies, session, and same-origin responses. Since these pages are part of the authentication flow, a victim following what appears to be a legitimate confirmation or sign-in link is a plausible target. This issue affects ash_authentication: from 4.8.0 before 4.14.2 and from 5.0.0-rc.0 before 5.0.0-rc.13.

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Meta Information

Published
2026-08-25
Last Modified
2026-08-25
Generated
2026-08-25
AI Q&A
2026-08-25
EPSS Evaluated
N/A
NVD
CVE-2026-66882
EUVD
EUVD-2026-65321

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
team-alembic ash_authentication From 4.8.0 (inc) to 4.14.2 (exc)
team-alembic ash_authentication From 5.0.0-rc.0 (inc) to 5.0.0-rc.13 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

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Executive Summary

This is a reflected cross-site scripting (XSS) vulnerability in the AshAuthentication library. It occurs when user-supplied input in URL parameters is embedded directly into HTML forms without proper escaping. Attackers can craft malicious URLs that inject executable scripts into confirmation or magic link interaction pages. These scripts execute in the context of the application, potentially accessing cookies, session data, and same-origin responses.

Detection Guidance

To detect this vulnerability, inspect your AshAuthentication forms for unescaped parameters in confirmation and magic link templates. Check for direct interpolation of user-supplied inputs like confirm or token parameters without HTML escaping. Review server logs for requests containing suspicious payloads such as script tags or attribute-breaking characters.

Impact Analysis

An unauthenticated attacker could trick users into clicking a malicious link, causing the injected script to run in the victim's browser. This could lead to theft of session cookies, sensitive data exposure, or unauthorized actions on behalf of the user within the application.

Compliance Impact

This XSS vulnerability could expose user data, violating GDPR's data protection principles or HIPAA's security requirements for safeguarding protected health information. It may lead to unauthorized access, data breaches, or loss of confidentiality, potentially resulting in regulatory penalties.

Mitigation Strategies

Upgrade AshAuthentication to version 4.14.2 or later for the 4.x branch, or 5.0.0-rc.13 or later for the 5.x branch. Apply the patches from the official commits that add Plug.HTML.html_escape/1 to confirmation and magic link templates. Disable require_interaction? if not required to reduce exposure.

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