CWE-185
Allowed-with-ReviewIncorrect Regular Expression
Abstraction: Class · Status: Draft
The product specifies a regular expression in a way that causes data to be improperly matched or compared.
71 vulnerabilities reference this CWE, most recent first.
GHSA-XRHX-7G5J-RCJ5
Vulnerability from github – Published: 2026-06-04 18:00 – Updated: 2026-06-04 18:00Summary
The ip-restriction middleware (hono/ip-restriction) compares incoming IP addresses against configured deny and allow rules using string equality after partial normalization. Non-canonical IPv6 representations of an address already listed in a static rule — such as compressed forms, explicit-zero forms, or hex-notation IPv4-mapped addresses — do not match the normalized rule entry, causing the rule to be silently skipped.
Details
When the rule matcher is built, each configured IP rule is normalized to a canonical string form. Incoming IP addresses received at request time are then compared against those canonical strings without applying the same normalization. Because IPv6 permits multiple syntactically different representations of the same numeric address, a non-canonical form of a denied address fails the string lookup and proceeds to the CIDR check, which also finds no match for rules registered as static (no prefix length). The request is then allowed.
Affected non-canonical forms include:
- Compressed versus expanded notation (
2001:db8::1vs2001:db8:0:0:0:0:0:1) - Hex-notation IPv4-mapped addresses (
::ffff:7f00:1vs::ffff:127.0.0.1) - Zone identifier suffixes (e.g.,
fe80::1%eth0)
Additionally, invalid IP address strings provided as the remote address are not rejected and may result in unexpected allow or deny behavior.
This issue arises when applications use ipRestriction() with static (non-CIDR) rules and the IP address source can supply addresses in non-canonical IPv6 form.
Impact
A request from an IP address covered by a static deny rule may bypass the restriction if the address is presented in a non-canonical IPv6 form.
This may lead to:
- Unauthorized access to endpoints intended to be restricted to specific IP addresses
- Bypass of IP-based access controls in environments where the runtime or an upstream proxy provides source addresses in a form that differs from the canonical form used in the rule configuration
This issue affects applications using hono/ip-restriction with static deny rules for IPv4 or IPv6 addresses, particularly when the source address is derived from proxy headers or custom getIP implementations that may return non-canonical forms.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "hono"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "4.12.21"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-47674"
],
"database_specific": {
"cwe_ids": [
"CWE-1289",
"CWE-185"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-04T18:00:22Z",
"nvd_published_at": "2026-05-28T17:16:32Z",
"severity": "MODERATE"
},
"details": "### Summary\n\nThe `ip-restriction` middleware (`hono/ip-restriction`) compares incoming IP addresses against configured deny and allow rules using string equality after partial normalization. Non-canonical IPv6 representations of an address already listed in a static rule \u2014 such as compressed forms, explicit-zero forms, or hex-notation IPv4-mapped addresses \u2014 do not match the normalized rule entry, causing the rule to be silently skipped.\n\n### Details\n\nWhen the rule matcher is built, each configured IP rule is normalized to a canonical string form. Incoming IP addresses received at request time are then compared against those canonical strings without applying the same normalization. Because IPv6 permits multiple syntactically different representations of the same numeric address, a non-canonical form of a denied address fails the string lookup and proceeds to the CIDR check, which also finds no match for rules registered as static (no prefix length). The request is then allowed.\n\nAffected non-canonical forms include:\n\n- Compressed versus expanded notation (`2001:db8::1` vs `2001:db8:0:0:0:0:0:1`)\n- Hex-notation IPv4-mapped addresses (`::ffff:7f00:1` vs `::ffff:127.0.0.1`)\n- Zone identifier suffixes (e.g., `fe80::1%eth0`)\n\nAdditionally, invalid IP address strings provided as the remote address are not rejected and may result in unexpected allow or deny behavior.\n\nThis issue arises when applications use `ipRestriction()` with static (non-CIDR) rules and the IP address source can supply addresses in non-canonical IPv6 form.\n\n### Impact\n\nA request from an IP address covered by a static deny rule may bypass the restriction if the address is presented in a non-canonical IPv6 form.\n\nThis may lead to:\n\n- Unauthorized access to endpoints intended to be restricted to specific IP addresses\n- Bypass of IP-based access controls in environments where the runtime or an upstream proxy provides source addresses in a form that differs from the canonical form used in the rule configuration\n\nThis issue affects applications using `hono/ip-restriction` with static deny rules for IPv4 or IPv6 addresses, particularly when the source address is derived from proxy headers or custom `getIP` implementations that may return non-canonical forms.",
"id": "GHSA-xrhx-7g5j-rcj5",
"modified": "2026-06-04T18:00:22Z",
"published": "2026-06-04T18:00:22Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/honojs/hono/security/advisories/GHSA-xrhx-7g5j-rcj5"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-47674"
},
{
"type": "WEB",
"url": "https://github.com/honojs/hono/commit/c831020fb1fa2e929d222f6c84e1abfe013e512b"
},
{
"type": "PACKAGE",
"url": "https://github.com/honojs/hono"
},
{
"type": "WEB",
"url": "https://github.com/honojs/hono/releases/tag/v4.12.21"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Hono: IP Restriction bypasses static deny rules for non-canonical IPv6 "
}
Mitigation MIT-45
Strategy: Refactoring
Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject the regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip through, then record the exploit and refactor the regular expression.
CAPEC-15: Command Delimiters
An attack of this type exploits a programs' vulnerabilities that allows an attacker's commands to be concatenated onto a legitimate command with the intent of targeting other resources such as the file system or database. The system that uses a filter or denylist input validation, as opposed to allowlist validation is vulnerable to an attacker who predicts delimiters (or combinations of delimiters) not present in the filter or denylist. As with other injection attacks, the attacker uses the command delimiter payload as an entry point to tunnel through the application and activate additional attacks through SQL queries, shell commands, network scanning, and so on.
CAPEC-6: Argument Injection
An attacker changes the behavior or state of a targeted application through injecting data or command syntax through the targets use of non-validated and non-filtered arguments of exposed services or methods.
CAPEC-79: Using Slashes in Alternate Encoding
This attack targets the encoding of the Slash characters. An adversary would try to exploit common filtering problems related to the use of the slashes characters to gain access to resources on the target host. Directory-driven systems, such as file systems and databases, typically use the slash character to indicate traversal between directories or other container components. For murky historical reasons, PCs (and, as a result, Microsoft OSs) choose to use a backslash, whereas the UNIX world typically makes use of the forward slash. The schizophrenic result is that many MS-based systems are required to understand both forms of the slash. This gives the adversary many opportunities to discover and abuse a number of common filtering problems. The goal of this pattern is to discover server software that only applies filters to one version, but not the other.