After upgrading cups and libcups2t64 to version
2.4.7-1.2ubuntu7.14 on Ubuntu 24.04, changing CUPS server
settings through system-config-printer no longer works.
The issue can also be reproduced with:
gdbus call --system \
--dest org.opensuse.CupsPkHelper.Mechanism \
--object-path / \
--method org.opensuse.CupsPkHelper.Mechanism.ServerSetSettings \
"{'_debug_logging': '0'}"
This appears to be a regression caused by the fix for
https://ubuntu.com/security/CVE-2025-61915.
Ubuntu’s cups-pk-helper package runs the main D-Bus helper as the
unprivileged cups-pk-helper user. After the CVE fix, CUPS requires
root peer credentials to rewrite cupsd.conf through the local CUPS
socket. Therefore, ServerSetSettings fails and server-setting changes
requested by system-config-printer are not applied.
I believe this issue may affect all cups-pk-helper versions based on
0.2.6-1ubuntu2 or later. Since this Ubuntu-specific change is present
from that version onward, the issue may affect all Ubuntu releases from
Focal onwards when using a CUPS version containing the CVE-2025-61915 fix.
** CVE added: https://cve.org/CVERecord?id=CVE-2025-61915
** Patch removed: "root-server-settings-backend.patch"
https://bugs.launchpad.net/ubuntu/+source/cups-pk-helper/+bug/2167414/+attachment/6000498/+files/root-server-settings-backend.patch
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https://bugs.launchpad.net/bugs/2167414
Title:
ServerSetSettings fails after CVE-2025-61915: non-root cups-pk-helper
cannot PUT cupsd.conf
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