FWIW, I got the same error trying to install CPAN with cpanp. 
export PERL5_CPANPLUS_HOME=/home/me
cpanp -i CPAN
[MSG] No '/home/me/.cpanplus/custom-sources' dir, skipping custom sour
+ces
[MSG] No '/home/me/.cpanplus/custom-sources' dir, skipping custom sour
+ces
[MSG] No '/home/me/.cpanplus/custom-sources' dir, skipping custom sour
+ces
Installing CPAN (2.37)
gpg: Signature made Fri Aug 30 13:11:50 2024 EDT
gpg:                using RSA key C40BA553F730173DA63AA20F7EFCE8AC421E
+E20A
gpg: requesting key 7EFCE8AC421EE20A from hkp://keyserver.ubuntu.com:1
+1371
gpg: Can't check signature: No public key
==> BAD/TAMPERED signature detected! <==
[ERROR] Signature check failed for module 'CPAN' -- Not trusting this 
+module, aborting install

[download]
but, turning off signatures worked. 
cpanp
CPAN Terminal> s conf signature 0
CPAN Terminal> i CPAN
Installing CPAN (2.37)

...

All tests successful.
Files=32, Tests=627, 217 wallclock secs ( 0.11 usr  0.14 sys + 23.52 c
+usr 85.69 csys = 109.46 CPU)
Result: PASS
*** Install log written to:
  /home/me/.cpanplus/install-logs/CPAN-2.37-1727728783.log

Module 'CPAN' installed successfully
No errors installing all modules

[download]
cpan CPAN and cpanm CPAN both worked without issue.

In reply to Re: GPG-Signed modules fail to install using cpanp under CygwinPerl by Danny
in thread GPG-Signed modules fail to install using cpanp under CygwinPerl by Intrepid

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