Grey has brought to our attention the "IdentTrust "armageddon", viewtopic.php?f=54&t=4136 pointing out that "Another horror story 
For XP SP3, macOS 10.12.0, Sony's PS3 and PS4 game consoles, Nintendo 3DS, iOS 9, etc." but also linking us to Scott Helme's post "Let's Encrypt's Root Certificate is expiring!", https://scotthelme.co.uk/lets-encrypt-o ... xpiration/.
Let's Encrypt is a provider of the application used to authenticate that the website you've reached is the one intended to be reached: the "s" in https. This is a good thing. When opening a new Amazon account I much prefer knowing that I am transmitting my banking account information to https://www.amazon.com/ than to http://www.amazoh.com/ or some web-site more ingeniously spoofing amazon's. One of the recommended Addons/Extensions for all web-browsers is "https everywhere".https://www.eff.org/https-everywhere
Let's Encrypt is not the only provider of such authenticating applications. But it is free and, thus, popular.
In reading the post Grey linked to, I noticed that among the devices effected which might be of concern to Puppians are:
OpenSSL <= 1.0.2
Mozilla Firefox < 50
Ubuntu < 16.04
Debian < 8
Java 8 < 8u141
Java 7 < 7u151
NSS < 3.26
*
I know nothing about NSS. I've noted it solely because those who know something might like to chime in.
The Java notations may not be much of a problem. As I understand it, newer versions of Java are backward compatible. So unless a newer version has dependencies which your Puppy can't meet, it should be a simple matter to just update the version you use*.
Debian 8 reached its end-of-life on June 30, 2020, five years after its initial release on April 26, 2015. EOL means Debian will not provide further security updates. We know it better under its code name Jessie. At least one Puppy, Pupjibaro Jessie, was woof-built employing its binaries.
Ubuntu 16.04 was released in April 2016 and reached EOL this last April. We know Ubuntu 16.04 better as Xenial Xerus whose binaries were used to woof Xenialpuppys.
Slackware 14.1 was release in November of 2013. I believe the Slacko 6.3 Puppys use its binaries. I'll leave it to other more familiar with Slackos to chime-in.
Web-browsers:
Firefox 50 was released in November 2016. Any Seamonkey <49 predates that. The same goes for Google-Chome and Chromium-Clones < 54.0.2840 including Opera 41 and its predecessors.
But the above release dates have greater significance. My guess is that any Puppy created before November 2016, or employing relevant binaries of that date or earlier will be effected. Among those Puppies would be the still popular Slacko 5.7 series, Lupus, Tahrpups, racys and Saluki/Carolinas.
But I think the major problem pertains to "OpenSSL <= 1.0.2", discussed here: viewtopic.php?p=37063#p37063
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* Although pzip and other encryption applications were not specifically mentioned, in the context of openssl dependencies, see this thread: viewtopic.php?p=35458#p35458
