ldap: cannot setup connect via cleartext ldap since 8.18.0 (Windows)

[yoneyajp]

I sometimes download CA's CRL.
Curl 8.17.0 can download CRL via ldap:// schema.

$ curl_o --version
curl 8.17.0 (x86_64-w64-mingw32) libcurl/8.17.0 LibreSSL/4.2.1 zlib/1.3.1.zlib-ng brotli/1.2.0 zstd/1.5.7 WinIDN libpsl/0.21.5 libssh2/1.11.1 nghttp2/1.68.0 ngtcp2/1.19.0 nghttp3/1.14.0
Release-Date: 2025-11-05
(snip)
$ curl_o -v -u : -o actalis.b64 'ldap://ldap.actalis.it/cn%3dActalis%20Server%20Authentication%20CA,ou%3dCertification%20Service%20Provider,o%3dActalis%20S.p.A.,c%3dIT?certificateRevocationList'
Note: Using embedded CA bundle, for proxies (225076 bytes)
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0* Host ldap.actalis.it:389 was resolved.
* IPv6: (none)
* IPv4: 109.70.240.128
*   Trying 109.70.240.128:389...
* Established connection to ldap.actalis.it (109.70.240.128 port 389) from 192.168.xx.xx port 58071
* LDAP local: LDAP Vendor = Microsoft Corporation. ; LDAP Version = 510
* LDAP local: ldap://ldap.actalis.it/cn%3dActalis%20Server%20Authentication%20CA,ou%3dCertification%20Service%20Provider,o%3dActalis%20S.p.A.,c%3dIT?certificateRevocationList
* LDAP local: trying to establish cleartext connection
{ [4 bytes data]
100  2477   0  2477   0     0  2238     0  --:--:--  0:00:01 --:--:--  2245
* shutting down connection #0
$ 

Meanwhile, since Curl 8.18.0, curl can't download CRL via ldap: schema.

$ curl --version
curl 8.19.0 (x86_64-w64-mingw32) libcurl/8.19.0 LibreSSL/4.2.1 zlib/1.3.1.zlib-ng brotli/1.2.0 zstd/1.5.7 WinIDN libpsl/0.21.5 libssh2/1.11.1 nghttp2/1.68.0 ngtcp2/1.21.0 nghttp3/1.15.0 WinLDAP
Release-Date: 2026-03-11
(snip)
$ curl -v -u : -o actalis.b64 'ldap://ldap.actalis.it/cn%3dActalis%20Server%20Authentication%20CA,ou%3dCertification%20Service%20Provider,o%3dActalis%20S.p.A.,c%3dIT?certificateRevocationList'
  % Total    % Received % Xferd  Average Speed  Time    Time    Time   Current
                                 Dload  Upload  Total   Spent   Left   Speed
  0      0   0      0   0      0      0      0                              0* Host ldap.actalis.it:389 was resolved.
* IPv6: (none)
* IPv4: 109.70.240.128
*   Trying 109.70.240.128:389...
* Established connection to ldap.actalis.it (109.70.240.128 port 389) from 192.168.xx.xx port 56352
* LDAP local: LDAP Vendor = Microsoft Corporation. ; LDAP Version = 510
* LDAP local: ldap://ldap.actalis.it/cn%3dActalis%20Server%20Authentication%20CA,ou%3dCertification%20Service%20Provider,o%3dActalis%20S.p.A.,c%3dIT?certificateRevocationList
* LDAP local: trying to establish cleartext connection
* LDAP: cannot setup connect to ldap.actalis.it:389

* shutting down connection #0
curl: (7) LDAP: cannot setup connect to ldap.actalis.it:389
$ 

Please let me know if I'm missing something important option(s) to indicate.
FYI, I'm using curl on Windows11 Home 25H2.

[vszakats]

Thanks for the report. Can't spot something build related, migrating to curl/curl.

[vszakats]

@yoneyajp Patch proposal in #20928.