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5 days before the Let’s Encrypt’s Root Certificate is expiring!

Posted by jpluimers on 2021/09/24

Only 5 days left to take a close look at both your web-clients (including back-end clients!) and servers to prevent potential Let’s Encrypt mayhem.

Last week, [Wayback] Scott Helme published about [Wayback/Archive.is] Let’s Encrypt’s Root Certificate is expiring!

Let’s Encrypt has done loads of work over the past lustrum to prevent trouble like cross-signing, issuing the successor certificates, and more.

The problem is that people like you and me have refrained from keeping their clients and servers up-to-date, so some security issues will occur. Hopefully they are limited to non-functioning communication and not leaking of data.

It is about this DST Root CA X3 certificate, used by the vast majority of Let’s Encrypt certificates, [Wayback/Archive.is] Certificate Checker: CN=DST Root CA X3, O=Digital Signature Trust Co.:

DST Root CA X3
Certificate Trusted anchor certificate
Subject DN CN=DST Root CA X3, O=Digital Signature Trust Co.
Issuer DN CN=DST Root CA X3, O=Digital Signature Trust Co.
Serial Number 44AFB080D6A327BA893039862EF8406B
Valid  to  Key RSAPublicKey (2048 bit)
SHA1 Hash DAC9024F54D8F6DF94935FB1732638CA6AD77C13 MD5 Hash 410352DC0FF7501B16F0028EBA6F45C5
SKI C4A7B1A47B2C71FADBE14B9075FFC41560858910 AKI

Quoting Scott, these clients likely will fail, so need attention:

  • OpenSSL <= 1.0.2
  • Windows < XP SP3
  • macOS < 10.12.1
  • iOS < 10 (iPhone 5 is the lowest model that can get to iOS 10)
  • Android < 7.1.1 (but >= 2.3.6 will work if served ISRG Root X1 cross-sign)
  • Mozilla Firefox < 50
  • Ubuntu < 16.04
  • Debian < 8
  • Java 8 < 8u141
  • Java 7 < 7u151
  • NSS < 3.26
  • Amazon FireOS (Silk Browser)

On the server side, you can help Android devices by using a Let’s Encrypt certificate that is cross-signed with the ISRG Root X1 certificate [Wayback/Archive.is] Certificate Checker: CN=ISRG Root X1, O=Internet Security Research Group, C=US:

ISRG Root X1
Certificate
Subject DN CN=ISRG Root X1, O=Internet Security Research Group, C=US
Issuer DN CN=DST Root CA X3, O=Digital Signature Trust Co.
Serial Number 4001772137D4E942B8EE76AA3C640AB7
Valid  to  Key RSAPublicKey (4096 bit)
SHA1 Hash 933C6DDEE95C9C41A40F9F50493D82BE03AD87BF MD5 Hash C1E1FF07F9F688498274D1A18053EABF
SKI 79B459E67BB6E5E40173800888C81A58F6E99B6E AKI C4A7B1A47B2C71FADBE14B9075FFC41560858910

Via [Archive.is] Scott Helme on Twitter: “There are only 10 days left until the Let’s Encrypt root certificate expires and there are still questions over what the impact will be! Full details here: …” which links to the above article showing a nice graph of the current Let’s Encrtypt root certificate setup:

–jeroen

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