Bug#1070033: libgnutls30: rejects numeric IPv6 addresses during connection

[Elliott Mitchell]

Package: libgnutls30
Version: 3.7.9-2+deb12u2
Severity: important

Long story to finding this one.  Trying to get LDAP setup on this
network.  As a recent deployment it seemed appropriate to use IPv6.

>From `nslcd` on clients I was getting the message:
nslcd[12345]: [1a2b3c] <group/member="root"> failed to bind to LDAP server ldaps://[fd12:3456:7890:abcd::3]/: Can't contact LDAP server: The TLS connection was non-properly terminated.: Resource temporarily unavailable

Running `nslcd` in debug mode failed to yield any additional useful
information.

Once I finally figured out `slapd`'s debug mode ('-h ldaps:/// ldapi:///'
is two arguments, the ldaps and ldapi are a single argument).  I got
traces from `slapd`: (serial numbers filed off)

tls_read: want=5, got=5
  0000:  16 03 01 01 8f

tls_read: want=399, got=399
  0160:    ............fd12  
  0170:    :3456:7890:abcd:  
  0180:    :3.-......... at .   
TLS: can't accept: A disallowed SNI server name has been received..
connection_read(13): TLS accept failure error=-1 id=1005, closing

Further tracing of the error message appears to point to the function
`_gnutls_dnsname_is_valid()` in gnutls/lib/str.h.  Seems libgnutls30 is
incompatible with numeric IPv6 addresses.

While IPv6-only hosts are presently uncommon, there is now quite a bit of
IPv6 traffic in many places.  I think this is worthy of having a severity
of "critical" as "bookworm" may remain as "stable" past when there is
more IPv6 traffic than IPv4 traffic.  For "trixie" this seems very
likely.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         ehem+sigmsg at m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445