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Base · Medium

CWE-807: Reliance on Untrusted Inputs in a Security Decision

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

CWE-807 · Base Level ·5 CVEs ·5 Mitigations

Description

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

Developers may assume that inputs such as cookies, environment variables, and hidden form fields cannot be modified. However, an attacker could change these inputs using customized clients or other attacks. This change might not be detected. When security decisions such as authentication and authorization are made based on the values of these inputs, attackers can bypass the security of the software. Without sufficient encryption, integrity checking, or other mechanism, any input that originates from an outsider cannot be trusted.

Potential Impact

Confidentiality, Access Control, Availability, Other

Bypass Protection Mechanism, Gain Privileges or Assume Identity, Varies by Context

Demonstrative Examples

The following code excerpt reads a value from a browser cookie to determine the role of the user.
Bad
Cookie[] cookies = request.getCookies();for (int i =0; i< cookies.length; i++) {Cookie c = cookies[i];if (c.getName().equals("role")) {userRole = c.getValue();}}
The following code could be for a medical records application. It performs authentication by checking if a cookie has been set.
Bad
$auth = $_COOKIES['authenticated'];if (! $auth) {if (AuthenticateUser($_POST['user'], $_POST['password']) == "success") {// save the cookie to send out in future responsessetcookie("authenticated", "1", time()+60*60*2);}else {ShowLoginScreen();die("\n");}}DisplayMedicalHistory($_POST['patient_ID']);
The programmer expects that the AuthenticateUser() check will always be applied, and the "authenticated" cookie will only be set when authentication succeeds. The programmer even diligently specifies a 2-hour expiration for the cookie.
However, the attacker can set the "authenticated" cookie to a non-zero value such as 1. As a result, the $auth variable is 1, and the AuthenticateUser() check is not even performed. The attacker has bypassed the authentication.
In the following example, an authentication flag is read from a browser cookie, thus allowing for external control of user state data.
Bad
Cookie[] cookies = request.getCookies();for (int i =0; i< cookies.length; i++) {Cookie c = cookies[i];if (c.getName().equals("authenticated") && Boolean.TRUE.equals(c.getValue())) {authenticated = true;}}
The following code samples use a DNS lookup in order to decide whether or not an inbound request is from a trusted host. If an attacker can poison the DNS cache, they can gain trusted status.
Bad
struct hostent *hp;struct in_addr myaddr;char* tHost = "trustme.example.com";myaddr.s_addr=inet_addr(ip_addr_string);
                     hp = gethostbyaddr((char *) &myaddr, sizeof(struct in_addr), AF_INET);if (hp && !strncmp(hp->h_name, tHost, sizeof(tHost))) {trusted = true;} else {trusted = false;}
Bad
String ip = request.getRemoteAddr();InetAddress addr = InetAddress.getByName(ip);if (addr.getCanonicalHostName().endsWith("trustme.com")) {trusted = true;}
Bad
IPAddress hostIPAddress = IPAddress.Parse(RemoteIpAddress);IPHostEntry hostInfo = Dns.GetHostByAddress(hostIPAddress);if (hostInfo.HostName.EndsWith("trustme.com")) {trusted = true;}
IP addresses are more reliable than DNS names, but they can also be spoofed. Attackers can easily forge the source IP address of the packets they send, but response packets will return to the forged IP address. To see the response packets, the attacker has to sniff the traffic between the victim machine and the forged IP address. In order to accomplish the required sniffing, attackers typically attempt to locate themselves on the same subnet as the victim machine. Attackers may be able to circumvent this requirement by using source routing, but source routing is disabled across much of the Internet today. In summary, IP address verification can be a useful part of an authentication scheme, but it should not be the single factor required for authentication.

Mitigations & Prevention

Architecture and Design

Store state information and sensitive data on the server side only. Ensure that the system definitively and unambiguously keeps track of its own state and user state and has rules defined for legitimate state transitions. Do not allow any application user to affect state directly in any way other than through legitimate actions leading to state transitions. If information must be stored on the client, do not do so without encryption and integrity checking,

Architecture and Design

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. With a stateless protocol such as HTTP, use a framework that maintains the state for you. Examples include ASP.NET View State [REF-756] and the OWASP ESAPI Session Management feature [REF-45]. Be careful of language features that provide state support, since these might be provided as a convenience

Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

OperationImplementation

When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

Architecture and DesignImplementation

Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls. Identify all inputs that are used for security decisions and determ

Detection Methods

  • Manual Static Analysis High — Since this weakness does not typically appear frequently within a single software package, manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all potentially-vulnerable operations can be assessed within limited time constraints.
  • Automated Static Analysis - Binary or Bytecode SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
  • Manual Static Analysis - Binary or Bytecode SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
  • Dynamic Analysis with Automated Results Interpretation SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
  • Dynamic Analysis with Manual Results Interpretation SOAR Partial — According to SOAR [REF-1479], the following detection techniques may be useful:
  • Manual Static Analysis - Source Code High — According to SOAR [REF-1479], the following detection techniques may be useful:

Real-World CVE Examples

CVE IDDescription
CVE-2009-1549Attacker can bypass authentication by setting a cookie to a specific value.
CVE-2009-1619Attacker can bypass authentication and gain admin privileges by setting an "admin" cookie to 1.
CVE-2009-0864Content management system allows admin privileges by setting a "login" cookie to "OK."
CVE-2008-5784e-dating application allows admin privileges by setting the admin cookie to 1.
CVE-2008-6291Web-based email list manager allows attackers to gain admin privileges by setting a login cookie to "admin."

CWE-693: Protection Mechanism Failure

The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed at...

Taxonomy Mappings

  • The CERT Oracle Secure Coding Standard for Java (2011): SEC09-J — Do not base security checks on untrusted sources

Frequently Asked Questions

What is CWE-807?

CWE-807 (Reliance on Untrusted Inputs in a Security Decision) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

How can CWE-807 be exploited?

Attackers can exploit CWE-807 (Reliance on Untrusted Inputs in a Security Decision) to bypass protection mechanism, gain privileges or assume identity, varies by context. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.

How do I prevent CWE-807?

Key mitigations include: Store state information and sensitive data on the server side only. Ensure that the system definitively and unambiguously keeps track of its own state and user state and has rules

What is the severity of CWE-807?

CWE-807 is classified as a Base-level weakness (Medium abstraction). It has been observed in 5 real-world CVEs.