CVE-2023-45683 (published 2023-10-16T19:15Z)

github.com/crewjam/saml is a saml library for the go language. In affected versions the package does not validate the ACS Location URI according to the SAML binding being parsed. If abused, this flaw allows attackers to register malicious Service Providers at the IdP and inject Javascript in the ACS endpoint definition, achieving Cross-Site-Scripting (XSS) in the IdP context during the redirection at the end of a SAML SSO Flow. Consequently, an attacker may perform any authenticated action as the victim once the victim’s browser loaded the SAML IdP initiated SSO link for the malicious service provider. Note: SP registration is commonly an unrestricted operation in IdPs, hence not requiring particular permissions or publicly accessible to ease the IdP interoperability. This issue is fixed in version 0.4.14. Users unable to upgrade may perform external validation of URLs provided in SAML metadata, or restrict the ability for end-users to upload arbitrary metadata.

CVSS v3 base score: 6.1, MEDIUM (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)

Weakness information:
cwe_id: CWE-79
cwe_name: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
description: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
extended_description: 
            Cross-site scripting (XSS) vulnerabilities occur when:
            
               Untrusted data enters a web application, typically from a web request.
               The web application dynamically generates a web page that contains this untrusted data.
               During page generation, the application does not prevent the data from containing content that is executable by a web browser, such as JavaScript, HTML tags, HTML attributes, mouse events, Flash, ActiveX, etc.
               A victim visits the generated web page through a web browser, which contains malicious script that was injected using the untrusted data.
               Since the script comes from a web page that was sent by the web server, the victim's web browser executes the malicious script in the context of the web server's domain.
               This effectively violates the intention of the web browser's same-origin policy, which states that scripts in one domain should not be able to access resources or run code in a different domain.
            
            There are three main kinds of XSS:
            
               
                  Type 1: Reflected XSS (or Non-Persistent) - 
         			The server reads data directly from the HTTP request and reflects it back in the HTTP response. Reflected XSS exploits occur when an attacker causes a victim to supply dangerous content to a vulnerable web application, which is then reflected back to the victim and executed by the web browser. The most common mechanism for delivering malicious content is to include it as a parameter in a URL that is posted publicly or e-mailed directly to the victim. URLs constructed in this manner constitute the core of many phishing schemes, whereby an attacker convinces a victim to visit a URL that refers to a vulnerable site. After the site reflects the attacker's content back to the victim, the content is executed by the victim's browser.
               
                  Type 2: Stored XSS (or Persistent) - 
               The application stores dangerous data in a database, message forum, visitor log, or other trusted data store. At a later time, the dangerous data is subsequently read back into the application and included in dynamic content. From an attacker's perspective, the optimal place to inject malicious content is in an area that is displayed to either many users or particularly interesting users. Interesting users typically have elevated privileges in the application or interact with sensitive data that is valuable to the attacker. If one of these users executes malicious content, the attacker may be able to perform privileged operations on behalf of the user or gain access to sensitive data belonging to the user. For example, the attacker might inject XSS into a log message, which might not be handled properly when an administrator views the logs.
            
               
                  Type 0: DOM-Based XSS - 
               In DOM-based XSS, the client performs the injection of XSS into the page; in the other types, the server performs the injection. DOM-based XSS generally involves server-controlled, trusted script that is sent to the client, such as Javascript that performs sanity checks on a form before the user submits it. If the server-supplied script processes user-supplied data and then injects it back into the web page (such as with dynamic HTML), then DOM-based XSS is possible.
            
            
            Once the malicious script is injected, the attacker can perform a variety of malicious activities. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. Phishing attacks could be used to emulate trusted web sites and trick the victim into entering a password, allowing the attacker to compromise the victim's account on that web site. Finally, the script could exploit a vulnerability in the web browser itself possibly taking over the victim's machine, sometimes referred to as "drive-by hacking."
            In many cases, the attack can be launched without the victim even being aware of it. Even with careful users, attackers frequently use a variety of methods to encode the malicious portion of the attack, such as URL encoding or Unicode, so the request looks less suspicious.
         
         

Fix information:
repo_url: https://github.com/crewjam/saml
commit_details: repo_url: https://github.com/crewjam/saml
author: Ross Kinder
author_date: 2023-10-14 10:18:46-04:00
msg: Merge pull request from GHSA-267v-3v32-g6q5
repository: repo_url: https://github.com/crewjam/saml
repo_name: crewjam/saml
description: SAML library for go
repo_language: Go
owner: crewjam
file_changes: filename: metadata.go
change_type: ModificationType.MODIFY
diff: @@ -2,6 +2,8 @@ package saml
 
 import (
 	"encoding/xml"
+	"fmt"
+	"net/url"
 	"time"
 
 	"github.com/beevik/etree"
@@ -19,6 +21,9 @@ const HTTPArtifactBinding = "urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Artifact"
 // SOAPBinding is the official URN for the SOAP binding (transport)
 const SOAPBinding = "urn:oasis:names:tc:SAML:2.0:bindings:SOAP"
 
+// SOAPBindingV1 is the URN for the SOAP binding in SAML 1.0
+const SOAPBindingV1 = "urn:oasis:names:tc:SAML:1.0:bindings:SOAP-binding"
+
 // EntitiesDescriptor represents the SAML object of the same name.
 //
 // See http://docs.oasis-open.org/security/saml/v2.0/saml-metadata-2.0-os.pdf §2.3.1
@@ -188,6 +193,76 @@ type Endpoint struct {
 	ResponseLocation string `xml:"ResponseLocation,attr,omitempty"`
 }
 
+func checkEndpointLocation(binding string, location string) (string, error) {
+	// Within the SAML standard, the complex type EndpointType describes a
+	// SAML protocol binding endpoint at which a SAML entity can be sent
+	// protocol messages. In particular, the location of an endpoint type is
+	// defined as follows in the Metadata for the OASIS Security Assertion
+	// Markup Language (SAML) V2.0 - 2.2.2 Complex Type EndpointType:
+	//
+	//   Location [Required] A required URI attribute that specifies the
+	//   location of the endpoint. The allowable syntax of this URI depends
+	//   on the protocol binding.
+	switch binding {
+	case HTTPPostBinding,
+		HTTPRedirectBinding,
+		HTTPArtifactBinding,
+		SOAPBinding,
+		SOAPBindingV1:
+		locationURL, err := url.Parse(location)
+		if err != nil {
+			return "", fmt.Errorf("invalid url %q: %w", location, err)
+		}
+		switch locationURL.Scheme {
+		case "http", "https":
+		// ok
+		default:
+			return "", fmt.Errorf("invalid url scheme %q for binding %q",
+				locationURL.Scheme, binding)
+		}
+	default:
+		// We don't know what form location should take, but the protocol
+		// requires that we validate its syntax.
+		//
+		// In practice, lots of metadata contains random bindings, for example
+		// "urn:mace:shibboleth:1.0:profiles:AuthnRequest" from our own test suite.
+		//
+		// We can't fail, but we also can't allow a location parameter whose syntax we
+		// cannot verify. The least-bad course of action here is to set location to
+		// and empty string, and hope the caller doesn't care need it.
+		location = ""
+	}
+
+	return location, nil
+}
+
+// UnmarshalXML implements xml.Unmarshaler
+func (m *Endpoint) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	type Alias Endpoint
+	aux := &struct {
+		*Alias
+	}{
+		Alias: (*Alias)(m),
+	}
+	if err := d.DecodeElement(aux, &start); err != nil {
+		return err
+	}
+
+	var err error
+	m.Location, err = checkEndpointLocation(m.Binding, m.Location)
+	if err != nil {
+		return err
+	}
+	if m.ResponseLocation != "" {
+		m.ResponseLocation, err = checkEndpointLocation(m.Binding, m.ResponseLocation)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // IndexedEndpoint represents the SAML IndexedEndpointType object.
 //
 // See http://docs.oasis-open.org/security/saml/v2.0/saml-metadata-2.0-os.pdf §2.2.3
@@ -199,6 +274,38 @@ type IndexedEndpoint struct {
 	IsDefault        *bool   `xml:"isDefault,attr"`
 }
 
+// UnmarshalXML implements xml.Unmarshaler
+func (m *IndexedEndpoint) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
+	type Alias IndexedEndpoint
+	aux := &struct {
+		*Alias
+	}{
+		Alias: (*Alias)(m),
+	}
+	if err := d.DecodeElement(aux, &start); err != nil {
+		return err
+	}
+
+	var err error
+	m.Location, err = checkEndpointLocation(m.Binding, m.Location)
+	if err != nil {
+		return err
+	}
+	if m.ResponseLocation != nil {
+		responseLocation, err := checkEndpointLocation(m.Binding, *m.ResponseLocation)
+		if err != nil {
+			return err
+		}
+		if responseLocation != "" {
+			m.ResponseLocation = &responseLocation
+		} else {
+			m.ResponseLocation = nil
+		}
+	}
+
+	return nil
+}
+
 // SSODescriptor represents the SAML complex type SSODescriptor
 //
 // See http://docs.oasis-open.org/security/saml/v2.0/saml-metadata-2.0-os.pdf §2.4.2

programming_language: Go
filename: metadata_test.go
change_type: ModificationType.MODIFY
diff: @@ -165,3 +165,11 @@ cvCsEFiJZ4AbF+DgmO6TarJ8O05t8zvnOwJlNCASPZRH/JmF8tX0hoHuAQ==`,
 	assert.Check(t, err)
 	golden.Assert(t, string(buf), "TestCanProduceSPMetadata_expected")
 }
+
+func TestMetadataValidatesUrlSchemeForProtocolBinding(t *testing.T) {
+	buf := golden.Get(t, "TestMetadataValidatesUrlSchemeForProtocolBinding_metadata.xml")
+
+	metadata := EntityDescriptor{}
+	err := xml.Unmarshal(buf, &metadata)
+	assert.Error(t, err, "invalid url scheme \"javascript\" for binding \"urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST\"")
+}

programming_language: Go
filename: TestMetadataValidatesUrlSchemeForProtocolBinding_metadata.xml
change_type: ModificationType.ADD
diff: @@ -0,0 +1 @@
+<?xml version='1.0' encoding='UTF-8'?><md:EntityDescriptor ID='_af805d1c-c2e3-444e-9cf5-efc664eeace6' entityID='https://dev.aa.kndr.org/users/auth/saml/metadata' validUntil='2001-02-03T04:05:06.789' cacheDuration='PT1H' xmlns:md='urn:oasis:names:tc:SAML:2.0:metadata' xmlns:saml='urn:oasis:names:tc:SAML:2.0:assertion'><md:SPSSODescriptor AuthnRequestsSigned='false' WantAssertionsSigned='false' protocolSupportEnumeration='urn:oasis:names:tc:SAML:2.0:protocol'><md:AssertionConsumerService Binding='urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST' Location='javascript:alert(true)' index='0' isDefault='true'/><md:AttributeConsumingService index='1' isDefault='true'><md:ServiceName xml:lang='en'>Required attributes</md:ServiceName><md:RequestedAttribute FriendlyName='Email address' Name='email' NameFormat='urn:oasis:names:tc:SAML:2.0:attrname-format:basic'/><md:RequestedAttribute FriendlyName='Full name' Name='name' NameFormat='urn:oasis:names:tc:SAML:2.0:attrname-format:basic'/><md:RequestedAttribute FriendlyName='Given name' Name='first_name' NameFormat='urn:oasis:names:tc:SAML:2.0:attrname-format:basic'/><md:RequestedAttribute FriendlyName='Family name' Name='last_name' NameFormat='urn:oasis:names:tc:SAML:2.0:attrname-format:basic'/></md:AttributeConsumingService></md:SPSSODescriptor></md:EntityDescriptor>
\ No newline at end of file

programming_language: PowerShell