crypto/x509: prevent HostnameError.Error() from consuming excessive resource
Constructing HostnameError.Error() takes O(N^2) runtime due to using a
string concatenation in a loop. Additionally, there is no limit on how
many names are included in the error message. As a result, a malicious
attacker could craft a certificate with an infinite amount of names to
unfairly consume resource.
To remediate this, we will now use strings.Builder to construct the
error message, preventing O(N^2) runtime. When a certificate has 100 or
more names, we will also not print each name individually.
Thanks to Philippe Antoine (Catena cyber) for reporting this issue.
Fixes #76445
Fixes CVE-2025-61729
Change-Id: I6343776ec3289577abc76dad71766c491c1a7c81
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/3000 Reviewed-by: Neal Patel <nealpatel@google.com> Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/725920 Reviewed-by: Roland Shoemaker <roland@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>