Opened 3 years ago

Closed 5 months ago

Last modified 4 months ago

#21608 closed Bug (fixed)

Logged out sessions are resurrected by concurrent requests

Reported by: jonasborgstrom Owned by: tltx
Component: contrib.sessions Version: 1.9
Severity: Normal Keywords:
Cc: m17.admin@…, tlt@… Triage Stage: Ready for checkin
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by jnnt)

  1. User logs in
  2. User loads a slow page in separate tab or as an ajax request, which modifies the session
  3. User logs out before request in step 2 completes. This will delete the session from the db

Expected behavior

User/session stays logged out since the user explicitly logged out and the session row was delete in step 3.

Actual behavior

The previously deleted session is re-inserted into the database when the request from step 2 completes. So the previously logged out user is now logged in again.

Attachments (2)

session_fix.patch (1.1 KB) - added by jonasborgstrom 3 years ago.
Proposed fix (against django 1.4)
21608.diff (2.7 KB) - added by tltx 7 months ago.

Download all attachments as: .zip

Change History (28)

Changed 3 years ago by jonasborgstrom

Proposed fix (against django 1.4)

comment:1 Changed 2 years ago by jonasborgstrom

  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset


comment:2 Changed 2 years ago by russellm

  • Needs tests set
  • Patch needs improvement set
  • Triage Stage changed from Unreviewed to Accepted

Seems like a reasonable request, and the patch looks like a decent start -- but it needs tests.

comment:3 Changed 2 years ago by nikl@…

  • Owner changed from nobody to anonymous
  • Status changed from new to assigned

comment:4 Changed 2 years ago by nikl@…

Finalized on the train and airport:

Thanks to everybody at DjangoIsland who helped me tackle this - looking forward to your feedback!

  • Nikl

comment:5 Changed 2 years ago by nikl@…

  • Has patch set
  • Needs tests unset
  • Patch needs improvement unset
  • Triage Stage changed from Accepted to Ready for checkin

comment:6 Changed 2 years ago by timo

  • Triage Stage changed from Ready for checkin to Accepted

Please don't mark your own patch as RFC. Someone who reviews the patch should do that.

comment:7 Changed 2 years ago by erikr

I'm not entirely getting this. When a user logs out, the session is flushed. Flushing the session clears it and deletes it. The database session store performs this deletion by actually deleting the record from the DB. The cached_db backend deletes it from the DB and the cache. So basically, all records of this session should be deleted. If you would post a new request with the now deleted session ID, Django will reject it, and assign you a new session with a new session ID.

The reporter says that django re-inserts the session when a request arrives with the old session ID, and will re-insert it with the old session data. But I don't see that anywhere in the code. As far as I can see, Django would reject the session ID, as loading would fail as the session object has been deleted, and the user would be assigned a new session. Even if there were a flaw in that logic: once the session data has been deleted, how would any code know how to recreate the session? The request doesn't contain any hint on what user should be logged in.

The only explanation I can come up with is that we're talking about cookie backed sessions, for which this is a documented limitation: you can't guarantee deletion of a cookie backed session or it's data, no matter what we do in Django: its the nature of cookies.

comment:8 Changed 2 years ago by timgraham

  • Patch needs improvement set

I couldn't reproduce this using steps 1-3 in the description (SQLite). After logging out in a separate tag, the slow page loaded, but subsequent requests redirected to the admin login page. There also seem to be some concerns from Nick's review on the PR.

comment:9 Changed 21 months ago by jonasborgstrom

I think one key detail missing from the initial reproduction steps is that the "slow page" needs to modify the session to make it dirty. Otherwise the session will not be resurrected.

Anyway, I've now create a complete reproduction test case here:

See README.txt for details.

comment:10 Changed 19 months ago by collinanderson

would fix this issue?

comment:11 Changed 14 months ago by sergeykolosov

  • Cc m17.admin@… added

comment:12 Changed 9 months ago by jnnt

  • Description modified (diff)

comment:13 Changed 8 months ago by tltx

I have reproduced this bug with the test site ( on both Django 1.8.7 and 1.9 (using SQLite).

These were the steps I used:

  • Open the admin page in a tab and log in. http://localhost:8000/admin/
  • Switch to a new tab and open the slow page. http://localhost:8000/slow/ Act fast after this step to complete the next three steps before the slow page has finished loaded, <10 sec
  • Switch back to tab with the admin page.
  • Click the "Logout" link on the top right corner of the page. -> Now you are on the logout page
  • Reload page -> Now you are on the login page.
  • Wait for slow page to finish loading.
  • Reload the tab with the login page.
  • Logged in again without entering credentials!

This is a security issue, not critical though, as someone might think that they have logged out but is actually still logged in.
If you logout and leave a public computer while a page is still loading in another tab there is a risk that the next person using that computer can get access to your account.
It would be nice to have this fixed in 1.8 and up.

Last edited 8 months ago by tltx (previous) (diff)

comment:14 Changed 8 months ago by tltx

  • Version changed from 1.4 to 1.8

comment:15 Changed 7 months ago by tltx

  • Cc tlt@… added
  • Owner changed from anonymous to tltx
  • Patch needs improvement unset
  • Version changed from 1.8 to 1.9

Changed 7 months ago by tltx

comment:16 Changed 7 months ago by tltx

  • Resolution set to fixed
  • Status changed from assigned to closed

comment:17 Changed 7 months ago by tltx

Run the unit test without the fix to verify the bug. This fix should also be back ported to 1.8 as it is a security fix.

comment:18 Changed 7 months ago by tltx

  • Resolution fixed deleted
  • Status changed from closed to new

comment:19 Changed 7 months ago by timgraham

Are you able to submit the patch as a pull request?

comment:20 Changed 7 months ago by tltx

Absolutely, which branch should I create a PR against?

comment:21 Changed 7 months ago by timgraham

Master please.

comment:22 Changed 7 months ago by tltx

Hi again, pull request is up.

comment:23 Changed 5 months ago by OakNinja

  • Triage Stage changed from Accepted to Ready for checkin

comment:24 Changed 5 months ago by OakNinja

I've gone through the patch review checklist and everything is looking good.

comment:25 Changed 5 months ago by Tim Graham <timograham@…>

  • Resolution set to fixed
  • Status changed from new to closed

In 3389c5e:

Fixed #21608 -- Prevented logged out sessions being resurrected by concurrent requests.

Thanks Simon Charette for the review.

comment:26 Changed 4 months ago by Tim Graham <timograham@…>

In 5faf745:

Refs #21608 -- Fixed incorrect cache key in cache session backend's save().

The bug was introduced commit 3389c5ea229884a1943873fe7e7ffc2800cefc22.

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