CVE-2026-6970

authd prior to version 0.6.4 contains a logic error in primary group ID assignment that can lead to local privilege escalation. When a user's primary group ID (GID) differs from their UID, either because the account was created with authd prior to version 0.5.4 or because the primary group was manually changed via the authctl group set-gid command, and the user's identity provider record is updated, authd incorrectly resets the user's primary group ID to their UID upon next login. This causes newly created files and directories to be owned by the wrong group, causing denial of service issues, and potentially granting unintended access to other local users and allowing local privilege escalation.

authd prior to version 0.6.4 contains a logic error in primary group ID assignment that can lead to local privilege escalation. When a user's primary group ID (GID) differs from their UID, either because the account was created with authd prior to version 0.5.4 or because the primary group was manually changed via the authctl group set-gid command, and the user's identity provider record is updated, authd incorrectly resets the user's primary group ID to their UID upon next login. This causes newly created files and directories to be owned by the wrong group, causing denial of service issues, and potentially granting unintended access to other local users and allowing local privilege escalation.

authd 0.6.0 contains a bug which can lead to an incorrect primary group ID.

It affects users whose primary group ID (i.e. the GID in the user record) differs from their UID. There are two ways which can lead to this:

1. The user was created with authd < 0.5.4 (released June 2025). Those users were created with UID != GID.

2. The primary group of the user was modified manually with the authctl utility that is shipped with authd (authctl group set-gid).

Another condition is that some user information must have changed in the identity provider (else the user record is not updated upon login). If that is the case, the next time an affected user logs in, authd will set their primary group ID to their UID.

This could lead to local privileges escalation. Also, files and directories created by those users will be owned by that incorrect primary group, which may grant other local users access to those files which they shouldn't have.

Users who are affected by the issue can run this script to fix the primary group ID of all authd users and the file ownership of files in the home directory created with the incorrect GID:

authd_users=$(getent passwd --service authd | cut -d: -f1)
for user in $authd_users; do
    OLD_GID=$(id -g "$user")
    GID=$(getent group "$user" | cut -d: -f3)
    if [ -z "$GID" ]; then
        echo "Warning: could not determine GID for $user, skipping" >&2
        continue
    fi
    if [ "$OLD_GID" = "$GID" ]; then
        continue  # user not affected
    fi
    USER_HOME=$(getent passwd "$user" | cut -d: -f6)
    echo "Fixing $user: resetting GID from $OLD_GID to $GID"
    sudo authctl group set-gid "$user" "$OLD_GID"
    sudo authctl group set-gid "$user" "$GID"
    sudo chown -R --from=":$OLD_GID" ":$GID" "$USER_HOME"
done

After applying the fix, affected users must log out and log back in for id, groups, and new file GID stamping to reflect the corrected primary group. You may also optionally terminate a user's active session with:

sudo loginctl terminate-user "$user"

If the users also own files outside their home directory, the ownership of those files might have to be updated as well.

Fixed by: https://github.com/canonical/authd/commit/154b428305cb1a7a19c897626fefd09d6dde8b9f

authd prior to version 0.6.4 contains a logic error in primary group ID assignment that can lead to local privilege escalation. When a user's primary group ID (GID) differs from their UID, either because the account was created with authd prior to version 0.5.4 or because the primary group was manually changed via the authctl group set-gid command, and the user's identity provider record is updated, authd incorrectly resets the user's primary group ID to their UID upon next login. This causes newly created files and directories to be owned by the wrong group, causing denial of service issues, and potentially granting unintended access to other local users and allowing local privilege escalation.

authd prior to version 0.6.4 contains a logic error in primary group ID assignment that can lead to local privilege escalation. When a user's primary group ID (GID) differs from their UID, either because the account was created with authd prior to version 0.5.4 or because the primary group was manually changed via the authctl group set-gid command, and the user's identity provider record is updated, authd incorrectly resets the user's primary group ID to their UID upon next login. This causes newly created files and directories to be owned by the wrong group, causing denial of service issues, and potentially granting unintended access to other local users and allowing local privilege escalation.

authd 0.6.0 contains a bug which can lead to an incorrect primary group ID.

It affects users whose primary group ID (i.e. the GID in the user record) differs from their UID. There are two ways which can lead to this:

1. The user was created with authd < 0.5.4 (released June 2025). Those users were created with UID != GID.

2. The primary group of the user was modified manually with the authctl utility that is shipped with authd (authctl group set-gid).

Another condition is that some user information must have changed in the identity provider (else the user record is not updated upon login). If that is the case, the next time an affected user logs in, authd will set their primary group ID to their UID.

This could lead to local privileges escalation. Also, files and directories created by those users will be owned by that incorrect primary group, which may grant other local users access to those files which they shouldn't have.

Users who are affected by the issue can run this script to fix the primary group ID of all authd users and the file ownership of files in the home directory created with the incorrect GID:

authd_users=$(getent passwd --service authd | cut -d: -f1)
for user in $authd_users; do
    OLD_GID=$(id -g "$user")
    GID=$(getent group "$user" | cut -d: -f3)
    if [ -z "$GID" ]; then
        echo "Warning: could not determine GID for $user, skipping" >&2
        continue
    fi
    if [ "$OLD_GID" = "$GID" ]; then
        continue  # user not affected
    fi
    USER_HOME=$(getent passwd "$user" | cut -d: -f6)
    echo "Fixing $user: resetting GID from $OLD_GID to $GID"
    sudo authctl group set-gid "$user" "$OLD_GID"
    sudo authctl group set-gid "$user" "$GID"
    sudo chown -R --from=":$OLD_GID" ":$GID" "$USER_HOME"
done

After applying the fix, affected users must log out and log back in for id, groups, and new file GID stamping to reflect the corrected primary group. You may also optionally terminate a user's active session with:

sudo loginctl terminate-user "$user"

If the users also own files outside their home directory, the ownership of those files might have to be updated as well.

Fixed by: https://github.com/canonical/authd/commit/154b428305cb1a7a19c897626fefd09d6dde8b9f