SpamAssassin sa-update fails with invalid config errors and update mirror failures

Symptoms

SpamAssassin may fail to start on new installations, suggesting that sa-update be run. However, sa-update fails with a lint check failure due to an invalid regex.

[root@server ~]# /usr/local/cpanel/3rdparty/bin/sa-update
config: invalid regexp for __URI_TRY_3LD 'm,^https?://(?:try(?!r\.codeschool)|start|get(?!\.adobe)|save|check(?!out)|act|compare|join|learn(?!ing)|request|visit(?!or|\.vermont)|my(?!sub|turbotax|news\.apple|a\.godaddy|account|support|build|blob)\w)[^.]*\.[^/]+\.(?<!list-manage\.)(?:com|net)\b,i': Variable length lookbehind is experimental in regex; marked by <-- HERE in m/(?i)^https?://(?:try(?!r\.codeschool)|start|get(?!\.adobe)|save|check(?!out)|act|compare|join|learn(?!ing)|request|visit(?!or|\.vermont)|my(?!sub|turbotax|news\.apple|a\.godaddy|account|support|build|blob)\w)[^.]*\.[^/]+\.(?<!list-manage\.)(?:com|net)\b <-- HERE /

channel 'updates.spamassassin.org': lint check of update failed, channel failed

Description

The sa-update utility, which installs the SpamAssassin rules, fails when linting (validating) the ruleset. This prevents sa-update from successfully installing the ruleset, which prevents spamd from starting due to missing configuration files.

The full details of this failure can be examined in the original defect report here:
Bug 7956 - config: invalid regexp for __URI_TRY_3LD

We've opened an internal case for our development team to investigate this further. For reference, the case number is UPS-429. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Run the following command.

   cp -av /var/lib/spamassassin /var/lib/spamassassin.$(date -u +%Y%m%d%H%M%S%Z) && cd /var/lib/spamassassin/3.004004/updates_spamassassin_org && wget -N http://sa-update.spamassassin.org/1898122.tar.gz{,.sha256,.sha512,.asc} && /usr/local/cpanel/3rdparty/bin/sa-update --verbose --install /var/lib/spamassassin/3.004004/updates_spamassassin_org/1898122.tar.gz && /usr/local/cpanel/scripts/restartsrv_spamd --restart