# Session fixation across login

A session known to an attacker remains usable after another controlled user authenticates into it.

**Candidate CWE:** [CWE-384](https://cwe.mitre.org/data/definitions/384.html)

## Test hypothesis

In the local replica, obtain an anonymous session and establish a realistic way to place it in B’s browser. After B logs in, replay the original session from A’s separate client.

## Evidence required

A’s client gains B’s authenticated identity using the previously known identifier. Document the delivery precondition and whether the server rotates or rebinds the credential.

## Rule out false positives

An unchanged analytics cookie or session name, or no feasible method to fix the victim’s session, does not prove account access.

## Playbook and command references

- [Authentication, recovery, federation, and session lifecycle](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/modules/identity-session.html) — Test registration, recovery, identity changes, invitations, SSO enforcement, and deprovisioning as one account state machine.

[Find the associated command snippets](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/commands.html?q=Authentication%2C%20recovery%2C%20federation%2C%20and%20session%20lifecycle)

## Referenced by these target playbooks

[Web & API](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/web-api.html) · [OSS & self-hosted](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/oss.html) · [Mobile](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/mobile.html) · [Desktop & extensions](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/desktop.html)

## Report checklist

- [ ] Capture the affected version, configuration, identities, and object ownership.
- [ ] Preserve a valid baseline and a negative control.
- [ ] Reproduce the forbidden data access, action, or state change on controlled fixtures.
- [ ] Explain the intended security rule and why the observed behavior violates it.
- [ ] State prerequisites, uncertainty, cleanup, and the smallest demonstrated impact.

## Conditional ATT&CK mapping

- [T1550.004 · Use Alternate Authentication Material: Web Session Cookie](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/attack.html#T1550-004) — **Only if:** A session cookie acquired across a security boundary is accepted in another controlled client to access the represented user's protected session. **Not established by:** A missing cookie flag, reflected cookie name, or untested assumption about MFA bypass is insufficient. Ordinary cookie-based login does not demonstrate compromise.

## Primary references

- [OWASP session management](https://cheatsheetseries.owasp.org/cheatsheets/Session_Management_Cheat_Sheet.html)

[Back to the complete vulnerability catalog](https://bug-bounty-field-manual.kmahshooq.chatgpt.site/vulnerabilities.html)