eef-cve-2026-86688
CVSS 7.4 osv_hex## Summary Session Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim's browser to hold an authenticated session once that victim signs in. `AshAuthentication.Plug.Helpers.store_in_session/2` writes the authenticated subject into the existing session with `Plug.Conn.put_session/3` and never calls `Plug.Conn.configure_session(renew: true)`, so the identifier the visitor arrived with carries into their authenticated session. Every authentication event reaches this one function: the default `success/4` injected by `AshAuthentication.Phoenix.Controller.__using__/1`, the `AuthController` emitted by `mix ash_authentication_phoenix.install`, and remember-me auto-login. `AshAuthentication.Phoenix.Plug.store_in_session/2` is a `defdelegate` to it. Logout does not close the window either, because `clear_session/2` ends with `Plug.Conn.clear_session/1`, which clears session contents but leaves the identifier intact, so a planted identifier survives a logout-then-login cycle. This issue affects ash_authentication: from 0.2.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14. ## Impact An attacker holding a session identifier they planted before the victim signed in gains that victim's authenticated session, and with it full account takeover, in deployments using a server-side session store. ## Workarounds Call `Plug.Conn.configure_session(conn, renew: true)` in your own `success/4` before `store_in_session/2`. This is a one-line change in application code and closes the controller sign-in path, though not remember-me auto-login, which does not pass through application code. Add `Plug.Conn.configure_session(conn, drop: true)` at sign-out so a planted identifier does not survive a logout-then-login cycle. ## Configurations Exploitation for account takeover requires a server-side session store (ETS, Mnesia, Redis or a database), where the cookie carries a stable session identifier, and a position from which the attacker can plant that cookie in the victim's browser: cookie tossing from a sibling subdomain, an HTTP host without HSTS, or a shared or kiosk browser. Phoenix defaults to the signed cookie store, and neither package's installer changes it. Under that store the authenticated session lives in the re-signed cookie delivered only to the victim, so a planted pre-authentication copy does not become an authenticated session. Attacker-planted session contents, such as a `return_to` value, still survive into the authenticated session there.
- Published
- unknown
- Last Modified
- unknown
CVSS details not available.
No product information available.
- https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-v577-944g-7h3x
- https://cna.erlef.org/cves/CVE-2026-86688.html
- https://github.com/team-alembic/ash_authentication/commit/a939dde9b917c072cdf10c4b0913a9886a4b0231
- https://github.com/team-alembic/ash_authentication/commit/872db454405ecad4fcdabd9ff3d8755d1d6a69ae
- https://github.com/team-alembic/ash_authentication/commit/3e1d452cbf1564e87f5f97be882b66fe25af7cfa
- https://hex.pm/packages/ash_authentication
No linked vulnerabilities found.
{
"affected": [
{
"database_specific": {
"source": "https://cna.erlef.org/osv/EEF-CVE-2026-86688.json"
},
"package": {
"ecosystem": "Hex",
"name": "ash_authentication",
"purl": "pkg:hex/ash_authentication"
},
"ranges": [
{
"events": [
{
"introduced": "0.2.0"
},
{
"fixed": "4.15.0"
}
],
"type": "SEMVER"
},
{
"events": [
{
"introduced": "5.0.0-rc.0"
},
{
"fixed": "5.0.0-rc.14"
}
],
"type": "SEMVER"
}
],
"versions": [
"3.0.3",
"3.1.0",
"3.10.0",
"3.10.1",
"3.10.2",
"3.10.3",
"3.10.4",
"3.10.5",
"3.10.6",
"3.10.7",
"3.10.8",
"3.11.0",
"3.11.1",
"3.11.10",
"3.11.11",
"3.11.12",
"3.11.13",
"3.11.14",
"3.11.15",
"3.11.16",
"3.11.2",
"3.11.3",
"3.11.4",
"3.11.5",
"3.11.6",
"3.11.7",
"3.11.8",
"3.11.9",
"3.12.0",
"3.12.1",
"3.12.2",
"3.12.3",
"3.12.4",
"3.2.0",
"3.2.1",
"3.2.2",
"3.3.0",
"3.3.1",
"3.5.0",
"3.5.1",
"3.5.2",
"3.5.3",
"3.6.0",
"3.6.1",
"3.7.0",
"3.7.1",
"3.7.2",
"3.7.3",
"3.7.4",
"3.7.5",
"3.7.6",
"3.7.8",
"3.7.9",
"3.8.0",
"3.9.0",
"3.9.1",
"3.9.2",
"3.9.3",
"3.9.4",
"3.9.5",
"3.9.6",
"4.0.0",
"4.0.0-rc.0",
"4.0.0-rc.1",
"4.0.0-rc.2",
"4.0.0-rc.3",
"4.0.0-rc.5",
"4.0.0-rc.6",
"4.0.1",
"4.0.2",
"4.0.3",
"4.0.4",
"4.1.0",
"4.10.0",
"4.11.0",
"4.12.0",
"4.13.0",
"4.13.1",
"4.13.2",
"4.13.3",
"4.13.4",
"4.13.5",
"4.13.6",
"4.13.7",
"4.14.0",
"4.14.1",
"4.14.2",
"4.2.0",
"4.2.1",
"4.2.2",
"4.2.3",
"4.2.4",
"4.2.5",
"4.2.6",
"4.2.7",
"4.3.0",
"4.3.1",
"4.3.10",
"4.3.11",
"4.3.12",
"4.3.2",
"4.3.3",
"4.3.4",
"4.3.5",
"4.3.6",
"4.3.7",
"4.3.8",
"4.3.9",
"4.4.0",
"4.4.1",
"4.4.2",
"4.4.3",
"4.4.4",
"4.4.5",
"4.4.6",
"4.4.7",
"4.4.8",
"4.4.9",
"4.5.0",
"4.5.1",
"4.5.2",
"4.5.3",
"4.5.4",
"4.5.5",
"4.5.6",
"4.6.0",
"4.6.1",
"4.6.2",
"4.6.3",
"4.6.4",
"4.7.0",
"4.7.1",
"4.7.2",
"4.7.3",
"4.7.4",
"4.7.5",
"4.7.6",
"4.8.0",
"4.8.1",
"4.8.2",
"4.8.3",
"4.8.5",
"4.8.6",
"4.8.7",
"4.9.0",
"4.9.1",
"4.9.2",
"4.9.3",
"4.9.4",
"4.9.5",
"4.9.6",
"4.9.7",
"4.9.8",
"4.9.9",
"5.0.0-rc.0",
"5.0.0-rc.1",
"5.0.0-rc.10",
"5.0.0-rc.11",
"5.0.0-rc.12",
"5.0.0-rc.13",
"5.0.0-rc.2",
"5.0.0-rc.3",
"5.0.0-rc.4",
"5.0.0-rc.5",
"5.0.0-rc.6",
"5.0.0-rc.7",
"5.0.0-rc.8",
"5.0.0-rc.9"
]
},
{
"database_specific": {
"source": "https://cna.erlef.org/osv/EEF-CVE-2026-86688.json"
},
"ranges": [
{
"events": [
{
"introduced": "a939dde9b917c072cdf10c4b0913a9886a4b0231"
},
{
"fixed": "872db454405ecad4fcdabd9ff3d8755d1d6a69ae"
},
{
"fixed": "3e1d452cbf1564e87f5f97be882b66fe25af7cfa"
}
],
"repo": "https://github.com/team-alembic/ash_authentication",
"type": "GIT"
}
],
"versions": [
"v4.14.2",
"v5.0.0-rc.13",
"v4.14.1",
"v5.0.0-rc.12",
"v5.0.0-rc.11",
"v5.0.0-rc.10",
"v4.14.0",
"v4.13.7",
"5.0.0-rc.9",
"5.0.0-rc.8",
"v5.0.0-rc.7",
"v5.0.0-rc.6",
"v5.0.0-rc.5",
"v5.0.0-rc.4",
"v5.0.0-rc.3",
"v5.0.0-rc.2",
"v5.0.0-rc.1",
"v5.0.0-rc.0",
"v4.13.6",
"v4.13.5",
"v4.13.4",
"v4.13.3",
"v4.13.2",
"v4.13.1",
"v4.13.0",
"v4.12.0",
"v4.11.0",
"v4.10.0",
"v4.9.9",
"v4.9.8",
"v4.9.7",
"v4.9.6",
"v4.9.5",
"v4.9.4",
"v4.9.3",
"v4.9.2",
"v4.9.1",
"v4.9.0",
"v4.8.7",
"v4.8.5",
"v4.8.4",
"v4.8.3",
"v4.8.2",
"v4.8.1",
"v4.8.0",
"v4.7.7",
"v4.7.6",
"v4.7.5",
"v4.7.4",
"v4.7.3",
"v4.7.2",
"v4.7.1",
"v4.7.0",
"v4.6.4",
"v4.6.3",
"v4.6.2",
"v4.6.1",
"v4.6.0",
"v4.5.6",
"v4.5.5",
"v4.5.4",
"v4.5.3",
"v4.5.2",
"v4.5.1",
"v4.4.9",
"v4.4.8",
"v4.4.7",
"v4.4.6",
"v4.4.5",
"v4.4.4",
"v4.4.3",
"v4.4.2",
"v4.4.1",
"v4.4.0",
"v4.3.12",
"v4.3.10",
"v4.3.9",
"v4.3.7",
"v4.3.6",
"v4.3.4",
"v4.3.3",
"v4.3.2",
"v4.3.1",
"v4.3.0",
"v4.2.7",
"v4.2.5",
"v4.2.3",
"v4.2.2",
"v4.2.1",
"v4.2.0",
"v4.1.0",
"v4.0.4",
"v4.0.3",
"v4.0.2",
"v4.0.1",
"v4.0.0",
"v4.0.0-rc.7",
"v4.0.0-rc.6",
"v4.0.0-rc.5",
"v4.0.0-rc.4",
"v4.0.0-rc.3",
"v4.0.0-rc.2",
"v4.0.0-rc.1",
"v4.0.0-rc.0",
"v3.12.4",
"v3.12.3",
"v3.12.2",
"v3.12.1",
"v3.12.0",
"v3.11.16",
"v3.11.15",
"v3.11.14",
"v3.11.13",
"v3.11.12",
"v3.11.10",
"v3.11.9",
"v3.11.8",
"v3.11.7",
"v3.11.6",
"v3.11.5",
"v3.11.4",
"v3.11.3",
"v3.11.2",
"v3.11.1",
"v3.11.0",
"v3.10.8",
"v3.10.7",
"v3.10.6",
"v3.10.5",
"v3.10.4",
"v3.10.2",
"v3.10.1",
"v3.10.0",
"v3.9.6",
"v3.9.5",
"v3.9.4",
"v3.9.3",
"v3.9.2",
"v3.9.0",
"v3.7.9",
"v3.7.8",
"v3.7.6",
"v3.7.5",
"v3.7.4",
"v3.7.3",
"v3.7.2",
"v3.7.1",
"v3.7.0",
"v3.6.1",
"v3.5.3",
"v3.5.2",
"v3.5.1",
"v3.5.0",
"v3.4.2",
"v3.4.1",
"v3.4.0",
"v3.3.1",
"v3.3.0",
"v3.2.2",
"v3.2.1",
"v3.2.0",
"v3.1.0",
"v3.0.4",
"v3.0.3",
"v3.0.2",
"v3.0.1",
"v3.0.0",
"v2.0.1",
"v2.0.0",
"v1.0.0",
"v0.6.1",
"v0.6.0",
"v0.5.0",
"v0.4.3",
"v0.4.2",
"v0.4.1",
"v0.3.0",
"v0.2.1",
"v0.2.0"
]
}
],
"aliases": [
"CVE-2026-86688",
"GHSA-v577-944g-7h3x"
],
"credits": [
{
"name": "Peter Ullrich",
"type": "REPORTER"
},
{
"name": "James Harton",
"type": "REMEDIATION_DEVELOPER"
},
{
"name": "Jonatan Männchen / EEF",
"type": "COORDINATOR"
}
],
"database_specific": {
"capec_ids": [
"CAPEC-61"
],
"cpe_ids": [
"cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:*"
],
"cwe_ids": [
"CWE-384"
]
},
"details": "## Summary\n\nSession Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim's browser to hold an authenticated session once that victim signs in.\n\n`AshAuthentication.Plug.Helpers.store_in_session/2` writes the authenticated subject into the existing session with `Plug.Conn.put_session/3` and never calls `Plug.Conn.configure_session(renew: true)`, so the identifier the visitor arrived with carries into their authenticated session. Every authentication event reaches this one function: the default `success/4` injected by `AshAuthentication.Phoenix.Controller.__using__/1`, the `AuthController` emitted by `mix ash_authentication_phoenix.install`, and remember-me auto-login. `AshAuthentication.Phoenix.Plug.store_in_session/2` is a `defdelegate` to it. Logout does not close the window either, because `clear_session/2` ends with `Plug.Conn.clear_session/1`, which clears session contents but leaves the identifier intact, so a planted identifier survives a logout-then-login cycle.\n\nThis issue affects ash_authentication: from 0.2.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.\n\n## Impact\n\nAn attacker holding a session identifier they planted before the victim signed in gains that victim's authenticated session, and with it full account takeover, in deployments using a server-side session store.\n\n## Workarounds\n\nCall `Plug.Conn.configure_session(conn, renew: true)` in your own `success/4` before `store_in_session/2`. This is a one-line change in application code and closes the controller sign-in path, though not remember-me auto-login, which does not pass through application code.\n\nAdd `Plug.Conn.configure_session(conn, drop: true)` at sign-out so a planted identifier does not survive a logout-then-login cycle.\n\n## Configurations\n\nExploitation for account takeover requires a server-side session store (ETS, Mnesia, Redis or a database), where the cookie carries a stable session identifier, and a position from which the attacker can plant that cookie in the victim's browser: cookie tossing from a sibling subdomain, an HTTP host without HSTS, or a shared or kiosk browser.\n\nPhoenix defaults to the signed cookie store, and neither package's installer changes it. Under that store the authenticated session lives in the re-signed cookie delivered only to the victim, so a planted pre-authentication copy does not become an authenticated session. Attacker-planted session contents, such as a `return_to` value, still survive into the authenticated session there.",
"id": "EEF-CVE-2026-86688",
"modified": "2026-09-17T22:11:00.019764599Z",
"published": "2026-09-17T21:58:00.853Z",
"references": [
{
"type": "ADVISORY",
"url": "https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-v577-944g-7h3x"
},
{
"type": "WEB",
"url": "https://cna.erlef.org/cves/CVE-2026-86688.html"
},
{
"type": "WEB",
"url": "https://github.com/team-alembic/ash_authentication/commit/a939dde9b917c072cdf10c4b0913a9886a4b0231"
},
{
"type": "FIX",
"url": "https://github.com/team-alembic/ash_authentication/commit/872db454405ecad4fcdabd9ff3d8755d1d6a69ae"
},
{
"type": "FIX",
"url": "https://github.com/team-alembic/ash_authentication/commit/3e1d452cbf1564e87f5f97be882b66fe25af7cfa"
},
{
"type": "PACKAGE",
"url": "https://hex.pm/packages/ash_authentication"
}
],
"schema_version": "1.9.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Session id is not renewed on authentication in ash_authentication, allowing session fixation"
}