CVE-2026-66882

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.

• CWE-79

• https://cna.erlef.org/cves/CVE-2026-66882.html
• https://github.com/team-alembic/ash_authentication/commit/0bd5199db066be22b2ca1ec8bc6109e5d62e6070
• https://github.com/team-alembic/ash_authentication/commit/62719710790a150a9eacab9c0a066e0d122d15be
• https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-54fc-x3hv-ffhw
• https://osv.dev/vulnerability/EEF-CVE-2026-66882
• https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-54fc-x3hv-ffhw

Published

Aug 25, 2026

Last Modified

Sep 1, 2026

Status

Deferred

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