Unexpected path length 4 for exit circuit X, purpose 5

Support Relay Operator
1

Hello bridge operators,

I have recently upgraded the tor version 0.4.7.7 of 3 bridges Im hosting. On all of them, I have some notice logs saying :

13:10:55 [NOTICE] Unexpected path length 4 for exit circuit 1008, purpose 5
11:39:55 [NOTICE] Unexpected path length 4 for exit circuit 979, purpose 5
10:08:55 [NOTICE] Unexpected path length 4 for exit circuit 957, purpose 5

Where the exit circuit increases more and more. On my other bridges, I don’t have this problem. These logs appear from time to time…

Do you also have this on your bridges ?
Thanks for your help

2

Yep, I have alike messages for one of my bridges.

3

Hey @Superpaul209 thanks for reporting this issue. I filled a ticket, so Tor devs can check:

4

Yes, I’m getting those, too. Tor on Windows. New OBFS4 bridge.

It started happening even before I’d had any clients connect, and continued after I’d had a couple client connections.

I’m unsure if it goes away over time, I’ve only been running it a couple days so far.

5

On my 2 bridges running tor 0.4.7.7 I can confirm this. It did not occur on previous tor version.

  • Ubuntu 22.04 LTS (jammy)
  • Tor from deb.torproject.net
  • Version: 0.4.7.7-1~jammy+1
  • 2 different VPS, no other service running

Frequently:

Unexpected path length 4 for exit circuit x, purpose 5

Very seldom:

Unexpected path length 4 for exit circuit x, purpose 14

Please let me know if you want/need more information.

6

Same here on Centos 8 Stream. Didn’t happen on earlier tor releases. Let me know if you need further information.

7

I just got my first:
Unexpected path length 4 for exit circuit x, purpose 14

I’ve gotten many:
Unexpected path length 4 for exit circuit x, purpose 5

Does anyone know what causes them?

8

I just had a thought… someone else was asking how to ship WireGuard UDP packets over the Tor network. I suggested UDPTunnel acting as a local proxy, connecting locally to a Tor OBFS4 node, then shipping that traffic out to the greater Tor network.

Might that be the cause of these notices in our logs? Usually Tor strips off one hop each time it receives traffic from another node, but it might not be doing that for a local connection, so the traffic reaches another node with 4 hops instead of the expected maximum 3. I don’t know… something for the devs to investigate.