Executar análise estática (SAST) na base de código à procura do padrão inseguro no fluxo de dados.
CWE-777 Variante Incompleto
Regular Expression without Anchors
This vulnerability occurs when a regular expression used for validation or sanitization lacks anchors, allowing unintended characters or malicious payloads to bypass security checks.
Definição
What is CWE-777?
This vulnerability occurs when a regular expression used for validation or sanitization lacks anchors, allowing unintended characters or malicious payloads to bypass security checks.
Anchors like ^ (start of string) and $ (end of string) are critical for security-focused regular expressions. Without them, your pattern only needs to match a portion of the input, not the entire string. This means an attacker can prepend or append malicious content to an otherwise valid value, effectively sneaking dangerous data past your filter.
The impact depends on the missing anchor and the application's context. For example, omitting the start anchor allows payloads before a valid pattern, while omitting the end anchor permits trailing malicious code. Always anchor regex patterns used for input validation, allowlisting, or sanitization to enforce a complete match from start to finish.
Impacto no mundo real
Real-world CVEs caused by CWE-777
-
Chain: Web UI for a Python RPC framework does not use regex anchors to validate user login emails (CWE-777), potentially allowing bypass of OAuth (CWE-1390).
Como os atacantes a exploram
Trajeto do atacante passo a passo
- 1
Consider a web application that supports multiple languages. It selects messages for an appropriate language by using the lang parameter.
- 2
The previous code attempts to match only alphanumeric values so that language values such as "english" and "french" are valid while also protecting against path traversal, CWE-22. However, the regular expression anchors are omitted, so any text containing at least one alphanumeric character will now pass the validation step. For example, the attack string below will match the regular expression.
- 3
If the attacker can inject code sequences into a file, such as the web server's HTTP request log, then the attacker may be able to redirect the lang parameter to the log file and execute arbitrary code.
- 4
This code uses a regular expression to validate an IP string prior to using it in a call to the "ping" command.
- 5
Since the regular expression does not have anchors (CWE-777), i.e. is unbounded without ^ or $ characters, then prepending a 0 or 0x to the beginning of the IP address will still result in a matched regex pattern. Since the ping command supports octal and hex prepended IP addresses, it will use the unexpectedly valid IP address (CWE-1389). For example, "0x63.63.63.63" would be considered equivalent to "99.63.63.63". As a result, the attacker could potentially ping systems that the attacker cannot reach directly.
Exemplo de código vulnerável
Vulnerable PHP
Consider a web application that supports multiple languages. It selects messages for an appropriate language by using the lang parameter.
$dir = "/home/cwe/languages";
$lang = $_GET['lang'];
if (preg_match("/[A-Za-z0-9]+/", $lang)) {
include("$dir/$lang");
}
else {
echo "You shall not pass!\n";
} Payload do atacante
The previous code attempts to match only alphanumeric values so that language values such as "english" and "french" are valid while also protecting against path traversal, CWE-22. However, the regular expression anchors are omitted, so any text containing at least one alphanumeric character will now pass the validation step. For example, the attack string below will match the regular expression.
../../etc/passwd Exemplo de código seguro
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.
Lista de verificação de prevenção
How to prevent CWE-777
- Implementation Be sure to understand both what will be matched and what will not be matched by a regular expression. Anchoring the ends of the expression will allow the programmer to define an allowlist strictly limited to what is matched by the text in the regular expression. If you are using a package that only matches one line by default, ensure that you can match multi-line inputs if necessary.
Sinais de deteção
How to detect CWE-777
Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.
Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.
Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.
O Plexicus deteta automaticamente o CWE-777 e abre um PR de correção em menos de 60 segundos.
O Codex Remedium analisa cada commit, identifica esta fraqueza exata e entrega um pull request pronto para revisão com o patch. Sem tickets. Sem transferências.
Perguntas frequentes O que é o CWE-777?
Qual a gravidade do CWE-777?
Que linguagens ou plataformas são afetadas pelo CWE-777?
Como posso prevenir o CWE-777?
Como é que o Plexicus deteta e corrige o CWE-777?
Onde posso saber mais sobre o CWE-777?
Frequently asked questions
O que é o CWE-777?
This vulnerability occurs when a regular expression used for validation or sanitization lacks anchors, allowing unintended characters or malicious payloads to bypass security checks.
Qual a gravidade do CWE-777?
A MITRE classifica a probabilidade de exploração como Média — a exploração é realista mas normalmente requer condições específicas.
Que linguagens ou plataformas são afetadas pelo CWE-777?
A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.
Como posso prevenir o CWE-777?
Be sure to understand both what will be matched and what will not be matched by a regular expression. Anchoring the ends of the expression will allow the programmer to define an allowlist strictly limited to what is matched by the text in the regular expression. If you are using a package that only matches one line by default, ensure that you can match multi-line inputs if necessary.
Como é que o Plexicus deteta e corrige o CWE-777?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-777 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.
Onde posso saber mais sobre o CWE-777?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/777.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
Weaknesses related to CWE-777
Pronto quando você estiver
Pare de pagar por desenvolvedor.
Comece a fechar o ciclo.
O Plexicus é o ASPM nativo de IA que verifica, filtra, corrige, pentesta e explica — de forma autónoma. Programadores ilimitados, repos ilimitados, ações de IA de utilização justa. Nível gratuito real, €269/mo anual quando estiver pronto.