`actions/checkout@v6` incompatible with `debian:testing` since March 24, 2026

[francesco-ballarin]

Hi,
I use actions/checkout@v6 with the docker image debian:testing, and since a couple of days ago all my actions are failing with the error

  /usr/bin/git -c protocol.version=2 fetch --no-tags --prune --no-recurse-submodules --depth=1 origin +[sha]:refs/remotes/origin/main
  Error: fatal: unable to access 'https://github.com/[project]/': Problem with the SSL CA cert (path? access rights?)

Simplest way to reproduce is to

1. use debian:testing as the container
2. add a step with

  export DEBIAN_FRONTEND="noninteractive"
  apt update -y -q
  apt install -y -qq git

before the step with actions/checkout@v6

On March 24, 2026 the openssl package in debian:testing was upgraded from 3.5.5 to 3.6.1,
see https://tracker.debian.org/news/1734034/openssl-361-3-migrated-to-testing/
so that may (or may not) what triggered the problem.

I am opening there because this does not feel like a debian issue, in the sense that git clone with https works correctly on my debian:testing laptop. In other words, the issue seems to be specific to the actions/checkout steps (maybe the Setting up auth step), but they are too complex for me to understand where the issue is specifically.

Thanks,
Francesco