RHEL9+, RSASHA1 and CVE-2025-8677

[Bjørn Mork]

Time to re-evaluate the default SHA1 policies on RHEL...

Quoting from https://bind9.readthedocs.io/en/v9.20.15/notes.html#security-fixes

 DNSSEC validation fails if matching but invalid DNSKEY is found. (CVE-2025-8677)

 Previously, if a matching but cryptographically invalid key was
 encountered during DNSSEC validation, the key was skipped and not
 counted towards validation failures. named now treats such DNSSEC keys
 as hard failures and the DNSSEC validation fails immediately, instead of
 continuing with the next DNSKEYs in the RRset.

IIUC, this means that any zone with a RSASHA1 key will now fail
validation on Redhat systems using default policies, even if other keys
are present.

Is that correct?  Is it intentional?

If correct, then I believe it will break a number of zones with leftover
RSASHA1 keys and signatures. Anyone still having such keys in their
zones should purge them ASAP.  And resolver operators running BIND on
RHEL9 should consider running

 update-crypto-policies --set DEFAULT:SHA1

to prevent unexpected failures.


Bjørn