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[release-branch.go1.25] crypto/x509: excluded subdomain constraints preclude wildcard SANs

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When evaluating name constraints in a certificate chain, the presence of
an excluded subdomain constraint (e.g., excluding "test.example.com")
should preclude the use of a wildcard SAN (e.g., "*.example.com").

Fixes #76442
Fixes #76464
Fixes CVE-2025-61727

Change-Id: I42a0da010cb36d2ec9d1239ae3f61cf25eb78bba
Reviewed-on: https://go-review.googlesource.com/c/go/+/724400
Reviewed-by: Nicholas Husin <nsh@golang.org>
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Neal Patel <nealpatel@google.com>
This commit is contained in:
Roland Shoemaker
2025-11-24 08:46:08 -08:00
committed by Cherry Mui
parent e1ce1bfa7f
commit 287017aceb
3 changed files with 60 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

34
src/crypto/x509/name_constraints_test.go
View File

@@ -1624,6 +1624,40 @@ var nameConstraintsTests = []nameConstraintsTest{
},
expectedError: "URI with IP",
},
// #87: subdomain excluded constraints preclude wildcard names
{
roots: []constraintsSpec{
{
bad: []string{"dns:foo.example.com"},
},
},
intermediates: [][]constraintsSpec{
{
{},
},
},
leaf: leafSpec{
sans: []string{"dns:*.example.com"},
},
expectedError: "\"*.example.com\" is excluded by constraint \"foo.example.com\"",
},
// #88: wildcard names are not matched by subdomain permitted constraints
{
roots: []constraintsSpec{
{
ok: []string{"dns:foo.example.com"},
},
},
intermediates: [][]constraintsSpec{
{
{},
},
},
leaf: leafSpec{
sans: []string{"dns:*.example.com"},
},
expectedError: "\"*.example.com\" is not permitted",
},
}
func makeConstraintsCACert(constraints constraintsSpec, name string, key *ecdsa.PrivateKey, parent *Certificate, parentKey *ecdsa.PrivateKey) (*Certificate, error) {

40
src/crypto/x509/verify.go
View File

@@ -429,7 +429,7 @@ func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
return reverseLabels, true
}
func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string, excluded bool, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
// If the constraint contains an @, then it specifies an exact mailbox
// name.
if strings.Contains(constraint, "@") {
@@ -442,10 +442,10 @@ func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string, reversedDom
// Otherwise the constraint is like a DNS constraint of the domain part
// of the mailbox.
return matchDomainConstraint(mailbox.domain, constraint, reversedDomainsCache, reversedConstraintsCache)
return matchDomainConstraint(mailbox.domain, constraint, excluded, reversedDomainsCache, reversedConstraintsCache)
}
func matchURIConstraint(uri *url.URL, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
func matchURIConstraint(uri *url.URL, constraint string, excluded bool, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
// From RFC 5280, Section 4.2.1.10:
// “a uniformResourceIdentifier that does not include an authority
// component with a host name specified as a fully qualified domain
@@ -474,7 +474,7 @@ func matchURIConstraint(uri *url.URL, constraint string, reversedDomainsCache ma
return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
}
return matchDomainConstraint(host, constraint, reversedDomainsCache, reversedConstraintsCache)
return matchDomainConstraint(host, constraint, excluded, reversedDomainsCache, reversedConstraintsCache)
}
func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
@@ -491,7 +491,7 @@ func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
return true, nil
}
func matchDomainConstraint(domain, constraint string, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
func matchDomainConstraint(domain, constraint string, excluded bool, reversedDomainsCache map[string][]string, reversedConstraintsCache map[string][]string) (bool, error) {
// The meaning of zero length constraints is not specified, but this
// code follows NSS and accepts them as matching everything.
if len(constraint) == 0 {
@@ -508,6 +508,11 @@ func matchDomainConstraint(domain, constraint string, reversedDomainsCache map[s
reversedDomainsCache[domain] = domainLabels
}
wildcardDomain := false
if len(domain) > 0 && domain[0] == '*' {
wildcardDomain = true
}
// RFC 5280 says that a leading period in a domain name means that at
// least one label must be prepended, but only for URI and email
// constraints, not DNS constraints. The code also supports that
@@ -534,6 +539,11 @@ func matchDomainConstraint(domain, constraint string, reversedDomainsCache map[s
return false, nil
}
if excluded && wildcardDomain && len(domainLabels) > 1 && len(constraintLabels) > 0 {
domainLabels = domainLabels[:len(domainLabels)-1]
constraintLabels = constraintLabels[:len(constraintLabels)-1]
}
for i, constraintLabel := range constraintLabels {
if !strings.EqualFold(constraintLabel, domainLabels[i]) {
return false, nil
@@ -553,7 +563,7 @@ func (c *Certificate) checkNameConstraints(count *int,
nameType string,
name string,
parsedName any,
match func(parsedName, constraint any) (match bool, err error),
match func(parsedName, constraint any, excluded bool) (match bool, err error),
permitted, excluded any) error {
excludedValue := reflect.ValueOf(excluded)
@@ -565,7 +575,7 @@ func (c *Certificate) checkNameConstraints(count *int,
for i := 0; i < excludedValue.Len(); i++ {
constraint := excludedValue.Index(i).Interface()
match, err := match(parsedName, constraint)
match, err := match(parsedName, constraint, true)
if err != nil {
return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
}
@@ -587,7 +597,7 @@ func (c *Certificate) checkNameConstraints(count *int,
constraint := permittedValue.Index(i).Interface()
var err error
if ok, err = match(parsedName, constraint); err != nil {
if ok, err = match(parsedName, constraint, false); err != nil {
return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
}
@@ -679,8 +689,8 @@ func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *V
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
func(parsedName, constraint any) (bool, error) {
return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
func(parsedName, constraint any, excluded bool) (bool, error) {
return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string), excluded, reversedDomainsCache, reversedConstraintsCache)
}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
return err
}
@@ -692,8 +702,8 @@ func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *V
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
func(parsedName, constraint any) (bool, error) {
return matchDomainConstraint(parsedName.(string), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
func(parsedName, constraint any, excluded bool) (bool, error) {
return matchDomainConstraint(parsedName.(string), constraint.(string), excluded, reversedDomainsCache, reversedConstraintsCache)
}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
return err
}
@@ -706,8 +716,8 @@ func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *V
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
func(parsedName, constraint any) (bool, error) {
return matchURIConstraint(parsedName.(*url.URL), constraint.(string), reversedDomainsCache, reversedConstraintsCache)
func(parsedName, constraint any, excluded bool) (bool, error) {
return matchURIConstraint(parsedName.(*url.URL), constraint.(string), excluded, reversedDomainsCache, reversedConstraintsCache)
}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
return err
}
@@ -719,7 +729,7 @@ func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *V
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
func(parsedName, constraint any) (bool, error) {
func(parsedName, constraint any, _ bool) (bool, error) {
return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
return err

2
src/crypto/x509/verify_test.go
View File

@@ -1352,7 +1352,7 @@ var nameConstraintTests = []struct {
func TestNameConstraints(t *testing.T) {
for i, test := range nameConstraintTests {
result, err := matchDomainConstraint(test.domain, test.constraint, map[string][]string{}, map[string][]string{})
result, err := matchDomainConstraint(test.domain, test.constraint, false, map[string][]string{}, map[string][]string{})
if err != nil && !test.expectError {
t.Errorf("unexpected error for test #%d: domain=%s, constraint=%s, err=%s", i, test.domain, test.constraint, err)