[Bug 2109831] Re: PerSourceMaxStartups setting now preventing all ssh access

[Nick Rosbrook]

I was able to confirm this behavior is present on plucky, but not
oracular.

I created a new LXD container, and ran:

$ echo "PerSourceMaxStartups 3" >> /etc/ssh/sshd_config.d/per-source-
max-startups.conf

Then I added a key to authorized_keys etc, and then made 4 connection
attempts from my host to the container. On the 4th attempt, the
connection failed. In the container, I saw:

$ journalctl -u ssh -b
May 02 19:03:12 p systemd[1]: Starting ssh.service - OpenBSD Secure Shell server...
May 02 19:03:12 p sshd[483]: Server listening on 0.0.0.0 port 22.
May 02 19:03:12 p sshd[483]: Server listening on :: port 22.
May 02 19:03:12 p systemd[1]: Started ssh.service - OpenBSD Secure Shell server.
May 02 19:03:16 p sshd-session[504]: Accepted publickey for ubuntu from 10.19.111.1 port 50302 ssh2: RSA SHA256:VMGz6tsZ02V9ratWlExePp9LaOe2qIr7SiWLHP2aGrM
May 02 19:03:16 p sshd-session[504]: pam_unix(sshd:session): session opened for user ubuntu(uid=1000) by ubuntu(uid=0)
May 02 19:03:18 p sshd-session[589]: Accepted publickey for ubuntu from 10.19.111.1 port 48300 ssh2: RSA SHA256:VMGz6tsZ02V9ratWlExePp9LaOe2qIr7SiWLHP2aGrM
May 02 19:03:18 p sshd-session[589]: pam_unix(sshd:session): session opened for user ubuntu(uid=1000) by ubuntu(uid=0)
May 02 19:03:21 p sshd-session[649]: Accepted publickey for ubuntu from 10.19.111.1 port 48308 ssh2: RSA SHA256:VMGz6tsZ02V9ratWlExePp9LaOe2qIr7SiWLHP2aGrM
May 02 19:03:21 p sshd-session[649]: pam_unix(sshd:session): session opened for user ubuntu(uid=1000) by ubuntu(uid=0)
May 02 19:03:24 p sshd[483]: error: beginning MaxStartups throttling
May 02 19:03:24 p sshd[483]: drop connection #0 from [10.19.111.1]:48320 on [10.19.111.16]:22 past Maxstartups
May 02 19:09:07 p sshd[483]: error: in MaxStartups throttling for 00:05:43, 3 connections dropped
May 02 19:09:07 p sshd[483]: drop connection #0 from [10.19.111.1]:39950 on [10.19.111.16]:22 past Maxstartups


** Changed in: openssh (Ubuntu)
       Status: New => Confirmed

** Changed in: openssh (Ubuntu)
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/2109831

Title:
  PerSourceMaxStartups setting now preventing all ssh access

Status in openssh package in Ubuntu:
  Confirmed

Bug description:
  I used to have "PerSourceMaxStartups 3" as a setting in a config file
  in /etc/ssh/sshd_config.d

  However, after the upgrade to Plucky this eventually prevents ALL ssh
  access to the system.

  It seems to allow 3 connexions, then denies all access until the ssh
  server is restarted.

  It was fine in Oracular.

  ProblemType: Bug
  DistroRelease: Ubuntu 25.04
  Package: openssh-server 1:9.9p1-3ubuntu3.1
  ProcVersionSignature: Ubuntu 6.14.0-15.15-generic 6.14.0
  Uname: Linux 6.14.0-15-generic x86_64
  ApportVersion: 2.32.0-0ubuntu5
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: KDE
  Date: Fri May  2 11:36:02 2025
  InstallationDate: Installed on 2024-10-12 (202 days ago)
  InstallationMedia: Kubuntu 24.10 "Oracular Oriole" - Release amd64 (20241007.6)
  SourcePackage: openssh
  UpgradeStatus: Upgraded to plucky on 2025-04-26 (5 days ago)

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