CVE-2026-86688 (GCVE-0-2026-86688)
Vulnerability from cvelistv5 – Published: 2026-09-17 21:58 – Updated: 2026-09-18 14:31
VLAI
EPSS
VEX
Title
Session id is not renewed on authentication in ash_authentication, allowing session fixation
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-18 14:24 UTC
CWE
- CWE-384 - Session Fixation
Assigner
References
6 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| team-alembic | ash_authentication |
Affected:
0.2.0 , < 4.15.0
(semver)
Affected: 5.0.0-rc.0 , < 5.0.0-rc.14 (semver) cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:* |
||
| team-alembic | ash_authentication |
Affected:
a939dde9b917c072cdf10c4b0913a9886a4b0231 , < *
(git)
cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:* |
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{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/team-alembic/ash_authentication/commit/a939dde9b917c072cdf10c4b0913a9886a4b0231"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-v577-944g-7h3x"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-86688"
}
],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Deferred",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-384"
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
]
}
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-86688",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-09-18T14:24:09.606894Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-09-18T14:29:32.046Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://repo.hex.pm",
"cpes": [
"cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"packageName": "ash_authentication",
"packageURL": "pkg:hex/ash_authentication",
"product": "ash_authentication",
"repo": "https://github.com/team-alembic/ash_authentication",
"vendor": "team-alembic",
"versions": [
{
"lessThan": "4.15.0",
"status": "affected",
"version": "0.2.0",
"versionType": "semver"
},
{
"lessThan": "5.0.0-rc.14",
"status": "affected",
"version": "5.0.0-rc.0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"packageName": "team-alembic/ash_authentication",
"packageURL": "pkg:github/team-alembic/ash_authentication",
"product": "ash_authentication",
"repo": "https://github.com/team-alembic/ash_authentication",
"vendor": "team-alembic",
"versions": [
{
"changes": [
{
"at": "872db454405ecad4fcdabd9ff3d8755d1d6a69ae",
"status": "unaffected"
},
{
"at": "3e1d452cbf1564e87f5f97be882b66fe25af7cfa",
"status": "unaffected"
}
],
"lessThan": "*",
"status": "affected",
"version": "a939dde9b917c072cdf10c4b0913a9886a4b0231",
"versionType": "git"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eExploitation 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\u0027s browser: cookie tossing from a sibling subdomain, an HTTP host without HSTS, or a shared or kiosk browser.\u003c/p\u003e\n\u003cp\u003ePhoenix defaults to the signed cookie store, and neither package\u0027s 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 \u003ccode\u003ereturn_to\u003c/code\u003e value, still survive into the authenticated session there.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "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\u0027s 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\u0027s 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."
}
],
"value": "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\u0027s 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\u0027s 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."
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:*",
"versionEndExcluding": "4.15.0",
"versionStartIncluding": "0.2.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:a:team-alembic:ash_authentication:*:*:*:*:*:*:*:*",
"versionEndExcluding": "5.0.0-rc.14",
"versionStartIncluding": "5.0.0-rc.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
],
"operator": "AND"
}
],
"credits": [
{
"lang": "en",
"type": "reporter",
"value": "Peter Ullrich"
},
{
"lang": "en",
"type": "remediation developer",
"value": "James Harton"
},
{
"lang": "en",
"type": "coordinator",
"value": "Jonatan M\u00e4nnchen / EEF"
}
],
"dateAssigned": "2026-09-17T05:24:11.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eSession Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim\u0027s browser to hold an authenticated session once that victim signs in.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eAshAuthentication.Plug.Helpers.store_in_session/2\u003c/code\u003e writes the authenticated subject into the existing session with \u003ccode\u003ePlug.Conn.put_session/3\u003c/code\u003e and never calls \u003ccode\u003ePlug.Conn.configure_session(renew: true)\u003c/code\u003e, so the identifier the visitor arrived with carries into their authenticated session. Every authentication event reaches this one function: the default \u003ccode\u003esuccess/4\u003c/code\u003e injected by \u003ccode\u003eAshAuthentication.Phoenix.Controller.__using__/1\u003c/code\u003e, the \u003ccode\u003eAuthController\u003c/code\u003e emitted by \u003ccode\u003emix ash_authentication_phoenix.install\u003c/code\u003e, and remember-me auto-login. \u003ccode\u003eAshAuthentication.Phoenix.Plug.store_in_session/2\u003c/code\u003e is a \u003ccode\u003edefdelegate\u003c/code\u003e to it. Logout does not close the window either, because \u003ccode\u003eclear_session/2\u003c/code\u003e ends with \u003ccode\u003ePlug.Conn.clear_session/1\u003c/code\u003e, which clears session contents but leaves the identifier intact, so a planted identifier survives a logout-then-login cycle.\u003c/p\u003e\n\u003cp\u003eThis 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.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Session Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim\u0027s 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."
}
],
"value": "Session Fixation vulnerability in team-alembic ash_authentication allows an attacker who can plant a session identifier in a victim\u0027s browser to hold an authenticated session once that victim signs in.\n\nAshAuthentication.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."
}
],
"impacts": [
{
"capecId": "CAPEC-61",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eAn attacker holding a session identifier they planted before the victim signed in gains that victim\u0027s authenticated session, and with it full account takeover, in deployments using a server-side session store.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "An attacker holding a session identifier they planted before the victim signed in gains that victim\u0027s authenticated session, and with it full account takeover, in deployments using a server-side session store."
}
],
"value": "An attacker holding a session identifier they planted before the victim signed in gains that victim\u0027s authenticated session, and with it full account takeover, in deployments using a server-side session store."
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"baseScore": 7.4,
"baseSeverity": "HIGH",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "ACTIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "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",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-384",
"description": "CWE-384 Session Fixation",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-17T21:58:00.853Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"name": "GitHub Advisory",
"tags": [
"related",
"vendor-advisory"
],
"url": "https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-v577-944g-7h3x"
},
{
"name": "EEF CNA record for CVE-2026-86688",
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-86688.html"
},
{
"name": "OSV record EEF-CVE-2026-86688",
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-86688"
},
{
"name": "Introducing commit a939dde in team-alembic/ash_authentication",
"tags": [
"related"
],
"url": "https://github.com/team-alembic/ash_authentication/commit/a939dde9b917c072cdf10c4b0913a9886a4b0231"
},
{
"name": "Fix commit 872db45 in team-alembic/ash_authentication",
"tags": [
"patch"
],
"url": "https://github.com/team-alembic/ash_authentication/commit/872db454405ecad4fcdabd9ff3d8755d1d6a69ae"
},
{
"name": "Fix commit 3e1d452 in team-alembic/ash_authentication",
"tags": [
"patch"
],
"url": "https://github.com/team-alembic/ash_authentication/commit/3e1d452cbf1564e87f5f97be882b66fe25af7cfa"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "Session id is not renewed on authentication in ash_authentication, allowing session fixation",
"workarounds": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eCall \u003ccode\u003ePlug.Conn.configure_session(conn, renew: true)\u003c/code\u003e in your own \u003ccode\u003esuccess/4\u003c/code\u003e before \u003ccode\u003estore_in_session/2\u003c/code\u003e. 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.\u003c/p\u003e\n\u003cp\u003eAdd \u003ccode\u003ePlug.Conn.configure_session(conn, drop: true)\u003c/code\u003e at sign-out so a planted identifier does not survive a logout-then-login cycle.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "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.\n\nAdd `Plug.Conn.configure_session(conn, drop: true)` at sign-out so a planted identifier does not survive a logout-then-login cycle."
}
],
"value": "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.\n\nAdd Plug.Conn.configure_session(conn, drop: true) at sign-out so a planted identifier does not survive a logout-then-login cycle."
}
]
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-86688",
"datePublished": "2026-09-17T21:58:00.853Z",
"dateReserved": "2026-09-17T00:30:01.485Z",
"dateUpdated": "2026-09-18T14:31:41.961Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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