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CWE-204 Base Incomplete
Observable Response Discrepancy
This vulnerability occurs when an application responds differently to similar requests, unintentionally leaking details about its internal state or logic to unauthorized users.
Definition
What is CWE-204?
This vulnerability occurs when an application responds differently to similar requests, unintentionally leaking details about its internal state or logic to unauthorized users.
Observable Response Discrepancy happens when an application's output—such as error messages, timing, or even subtle differences in page content—changes based on internal conditions. Attackers can probe these differences to infer sensitive information, like whether a username exists, if a file is present on the server, or the structure of a backend database, without triggering standard access controls.
To prevent this, developers must ensure their applications provide consistent, generic responses in all scenarios that could reveal system state. This involves standardizing error messages, implementing uniform response times for all outcomes (success or failure), and avoiding any output that changes based on hidden internal data. Treating all failed operations identically from the user's perspective closes this common information leak.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-204
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This, and others, use ".." attacks and monitor error responses, so there is overlap with directory traversal.
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Enumeration of valid usernames based on inconsistent responses
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Account number enumeration via inconsistent responses.
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User enumeration via discrepancies in error messages.
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User enumeration via discrepancies in error messages.
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Bulletin Board displays different error messages when a user exists or not, which makes it easier for remote attackers to identify valid users and conduct a brute force password guessing attack.
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Operating System, when direct remote login is disabled, displays a different message if the password is correct, which allows remote attackers to guess the password via brute force methods.
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Product allows remote attackers to determine if a port is being filtered because the response packet TTL is different than the default TTL.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
The following code checks validity of the supplied username and password and notifies the user of a successful or failed login.
- 2
In the above code, there are different messages for when an incorrect username is supplied, versus when the username is correct but the password is wrong. This difference enables a potential attacker to understand the state of the login function, and could allow an attacker to discover a valid username by trying different values until the incorrect password message is returned. In essence, this makes it easier for an attacker to obtain half of the necessary authentication credentials.
- 3
While this type of information may be helpful to a user, it is also useful to a potential attacker. In the above example, the message for both failed cases should be the same, such as:
Verwundbares Codebeispiel
Vulnerable Perl
The following code checks validity of the supplied username and password and notifies the user of a successful or failed login.
my $username=param('username');
my $password=param('password');
if (IsValidUsername($username) == 1)
{
if (IsValidPassword($username, $password) == 1)
{
print "Login Successful";
}
else
{
print "Login Failed - incorrect password";
}
}
else
{
print "Login Failed - unknown username";
} Sicheres Codebeispiel
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Präventions-Checkliste
How to prevent CWE-204
- Architecture and Design Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
- Implementation Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not.
Erkennungssignale
How to detect CWE-204
Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.
Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.
Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.
CWE-204
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Häufig gestellte Fragen Was ist CWE-204?
Wie gravierend ist CWE-204?
Welche Sprachen oder Plattformen sind von CWE-204 betroffen?
Wie kann ich CWE-204 verhindern?
Wie erkennt und behebt Plexicus CWE-204?
Wo erfahre ich mehr über CWE-204?
Frequently asked questions
Was ist CWE-204?
This vulnerability occurs when an application responds differently to similar requests, unintentionally leaking details about its internal state or logic to unauthorized users.
Wie gravierend ist CWE-204?
MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.
Welche Sprachen oder Plattformen sind von CWE-204 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-204 verhindern?
Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to…
Wie erkennt und behebt Plexicus CWE-204?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-204 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.
Wo erfahre ich mehr über CWE-204?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/204.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-204
CWE-203 Parent
Observable Discrepancy
This vulnerability occurs when an application responds differently to unauthorized users based on internal conditions. Attackers can…
CWE-1300 Sibling
Improper Protection of Physical Side Channels
This vulnerability occurs when a hardware device lacks adequate safeguards against physical side-channel attacks. Attackers can exploit…
CWE-1303 Sibling
Non-Transparent Sharing of Microarchitectural Resources
This vulnerability occurs when a processor's internal performance features, like caches and branch predictors, are unintentionally shared…
CWE-205 Sibling
Observable Behavioral Discrepancy
This vulnerability occurs when an application behaves differently in ways that unauthorized users can detect. These observable differences…
CWE-208 Sibling
Observable Timing Discrepancy
This vulnerability occurs when an application takes measurably different amounts of time to perform different operations, such as checking…
Ressourcen
Further reading
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Bereit zu validieren, was zählt.
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