The product uses a regular expression to perform neutralization, but the regular expression is not anchored and may allow malicious or malformed data to slip through.
View on MITREWhen performing tasks such as validating against a set of allowed inputs (allowlist), data is examined and possibly modified to ensure that it is well-formed and adheres to a list of safe values. If the regular expression is not anchored, malicious or malformed data may be included before or after any string matching the regular expression. The type of malicious data that is allowed will depend on the context of the application and which anchors are omitted from the regular expression.
An unanchored regular expression in the context of an allowlist will possibly result in a protection mechanism failure, allowing malicious or malformed data to enter trusted regions of the program. The specific consequences will depend on what functionality the allowlist was protecting.
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.
No detection method information available for this CWE.
Consider a web application that supports multiple languages. It selects messages for an appropriate language by using the lang parameter.
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.
This code uses a regular expression to validate an IP string prior to using it in a call to the "ping" command.
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.
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).
View DetailsCWE-777: Regular Expression without Anchors is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product uses a regular expression to perform neutralization, but the regular expression is not anchored and may allow malicious or malformed data to slip through. When performing tasks such as validating against a set of allowed inputs (allowlist), data is examined and possibly modified to ensure that it is well-formed and adheres to a list of safe values. If the regular expression is not anchored, malicious or malformed data may be included before or after any string matching the regular expression. The type of malicious data that is allowed will depend on the context of the application and which anchors are omitted from the regular expression.
If exploited, CWE-777 (Regular Expression without Anchors) it can compromise Availability, Confidentiality and Access Control, leading to outcomes such as Bypass Protection Mechanism.
Recommended mitigations for CWE-777 include: 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.
MITRE documents real CVEs mapped to CWE-777, including CVE-2022-30034. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
A CWE (Common Weakness Enumeration) like CWE-777 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.