# CVE-2026-86688: Session id is not renewed on authentication in ash_authentication, allowing session fixation

> Attackers can hijack user accounts by planting session identifiers that persist after login due to missing session renewal in ash_authentication.

- **Severity:** High 7.4 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** EEF-CVE-2026-86688, GHSA-v577-944g-7h3x

## What is CVE-2026-86688?

CVE-2026-86688 is a high-severity authentication bypass vulnerability in team-alembic ash_authentication, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-384 (Session Fixation)

## Which versions are affected by CVE-2026-86688?

1 open source package ship an affected version, including ash_authentication.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_authentication` | Hex | From 0.2.0 | 4.15.0, 5.0.0-rc.14 |

## How do I fix CVE-2026-86688?

Upgrade ash_authentication to a fixed version for your release line: 4.15.0 or 5.0.0-rc.14.

## Is CVE-2026-86688 being exploited?

There is no known exploitation of CVE-2026-86688 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86688 and fix it if it is affected.

What it is: CVE-2026-86688 is a high-severity authentication bypass vulnerability in team-alembic ash_authentication, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-86688 in the wild and no public exploit code.

Affected packages and fixed versions:
- ash_authentication (Hex): affected from 0.2.0; fixed in 4.15.0, 5.0.0-rc.14

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-86688/ (Markdown: https://insights.sbomify.com/CVE-2026-86688/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86688
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86688
- OSV: https://osv.dev/vulnerability/CVE-2026-86688

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86688/
Summaries are generated and may contain mistakes; the official description above is the record.