CWE-400
DiscouragedUncontrolled Resource Consumption
Abstraction: Class · Status: Draft
The product does not properly control the allocation and maintenance of a limited resource.
5435 vulnerabilities reference this CWE, most recent first.
GHSA-992Q-W5XV-32HH
Vulnerability from github – Published: 2026-06-16 15:33 – Updated: 2026-06-16 18:32Denial-of-service in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 152.
{
"affected": [],
"aliases": [
"CVE-2026-12319"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-06-16T13:16:32Z",
"severity": "MODERATE"
},
"details": "Denial-of-service in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 152.",
"id": "GHSA-992q-w5xv-32hh",
"modified": "2026-06-16T18:32:37Z",
"published": "2026-06-16T15:33:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-12319"
},
{
"type": "WEB",
"url": "https://bugzilla.mozilla.org/show_bug.cgi?id=2026933"
},
{
"type": "WEB",
"url": "https://www.mozilla.org/security/advisories/mfsa2026-57"
},
{
"type": "WEB",
"url": "https://www.mozilla.org/security/advisories/mfsa2026-60"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-9978-P96M-85PJ
Vulnerability from github – Published: 2022-05-24 17:41 – Updated: 2025-04-23 21:30A vulnerability was found in openvswitch. A limitation in the implementation of userspace packet parsing can allow a malicious user to send a specially crafted packet causing the resulting megaflow in the kernel to be too wide, potentially causing a denial of service. The highest threat from this vulnerability is to system availability.
{
"affected": [],
"aliases": [
"CVE-2020-35498"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2021-02-11T18:15:00Z",
"severity": "HIGH"
},
"details": "A vulnerability was found in openvswitch. A limitation in the implementation of userspace packet parsing can allow a malicious user to send a specially crafted packet causing the resulting megaflow in the kernel to be too wide, potentially causing a denial of service. The highest threat from this vulnerability is to system availability.",
"id": "GHSA-9978-p96m-85pj",
"modified": "2025-04-23T21:30:29Z",
"published": "2022-05-24T17:41:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2020-35498"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=1908845"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2021/02/msg00032.html"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UJ4DXFJWMZ325ECZXPZOSK7BOEDJZHPR"
},
{
"type": "WEB",
"url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UJ4DXFJWMZ325ECZXPZOSK7BOEDJZHPR"
},
{
"type": "WEB",
"url": "https://security.gentoo.org/glsa/202311-16"
},
{
"type": "WEB",
"url": "https://www.debian.org/security/2021/dsa-4852"
},
{
"type": "WEB",
"url": "https://www.openwall.com/lists/oss-security/2021/02/10/4"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-997P-PQQ2-W5F5
Vulnerability from github – Published: 2024-04-12 03:30 – Updated: 2024-04-12 03:30A denial of service vulnerability was identified in GitLab CE/EE, versions 16.7.7 prior to 16.8.6, 16.9 prior to 16.9.4 and 16.10 prior to 16.10.2 which allows an attacker to spike the GitLab instance resources usage resulting in service degradation via chat integration feature.
{
"affected": [],
"aliases": [
"CVE-2023-6489"
],
"database_specific": {
"cwe_ids": [
"CWE-1333",
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-04-12T01:15:57Z",
"severity": "MODERATE"
},
"details": "A denial of service vulnerability was identified in GitLab CE/EE, versions 16.7.7 prior to 16.8.6, 16.9 prior to 16.9.4 and 16.10 prior to 16.10.2 which allows an attacker to spike the GitLab instance resources usage resulting in service degradation via chat integration feature.",
"id": "GHSA-997p-pqq2-w5f5",
"modified": "2024-04-12T03:30:42Z",
"published": "2024-04-12T03:30:42Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-6489"
},
{
"type": "WEB",
"url": "https://hackerone.com/reports/2262450"
},
{
"type": "WEB",
"url": "https://gitlab.com/gitlab-org/gitlab/-/issues/433520"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-998W-HGHJ-9WH4
Vulnerability from github – Published: 2022-05-13 01:45 – Updated: 2022-05-13 01:45A vulnerability in the web user interface of Cisco IOS XE 3.1 through 3.17 could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to insufficient resource handling by the affected software when the web user interface is under a high load. An attacker could exploit this vulnerability by sending a high number of requests to the web user interface of the affected software. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. To exploit this vulnerability, the attacker must have access to the management interface of the affected software, which is typically connected to a restricted management network. This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS XE Software, if the web user interface of the software is enabled. By default, the web user interface is not enabled. Cisco Bug IDs: CSCup70353.
{
"affected": [],
"aliases": [
"CVE-2017-3856"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2017-03-22T19:59:00Z",
"severity": "HIGH"
},
"details": "A vulnerability in the web user interface of Cisco IOS XE 3.1 through 3.17 could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to insufficient resource handling by the affected software when the web user interface is under a high load. An attacker could exploit this vulnerability by sending a high number of requests to the web user interface of the affected software. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. To exploit this vulnerability, the attacker must have access to the management interface of the affected software, which is typically connected to a restricted management network. This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS XE Software, if the web user interface of the software is enabled. By default, the web user interface is not enabled. Cisco Bug IDs: CSCup70353.",
"id": "GHSA-998w-hghj-9wh4",
"modified": "2022-05-13T01:45:56Z",
"published": "2022-05-13T01:45:56Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2017-3856"
},
{
"type": "WEB",
"url": "https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170322-webui"
},
{
"type": "WEB",
"url": "http://www.securityfocus.com/bid/97007"
},
{
"type": "WEB",
"url": "http://www.securitytracker.com/id/1038101"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-99F4-GRH7-6PCQ
Vulnerability from github – Published: 2026-06-11 13:27 – Updated: 2026-06-11 13:27Impact
An invalid incoming compressed message can cause a client or server process to crash. This affects all clients and servers that use @grpc/grpc-js
Patches
The following version have fixes for this vulnerability:
- 1.9.16
- 1.10.12
- 1.11.4
- 1.12.7
- 1.13.5
- 1.14.4
Workarounds
There is no workaround.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.9.16"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "1.10.0"
},
{
"fixed": "1.10.12"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "1.11.0"
},
{
"fixed": "1.11.4"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "1.12.0"
},
{
"fixed": "1.12.7"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "1.13.0"
},
{
"fixed": "1.13.5"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "@grpc/grpc-js"
},
"ranges": [
{
"events": [
{
"introduced": "1.14.0"
},
{
"fixed": "1.14.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-48069"
],
"database_specific": {
"cwe_ids": [
"CWE-248",
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-11T13:27:44Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### Impact\nAn invalid incoming compressed message can cause a client or server process to crash. This affects all clients and servers that use @grpc/grpc-js\n\n### Patches\nThe following version have fixes for this vulnerability:\n\n - 1.9.16\n - 1.10.12\n - 1.11.4\n - 1.12.7\n - 1.13.5\n - 1.14.4\n\n### Workarounds\nThere is no workaround.",
"id": "GHSA-99f4-grh7-6pcq",
"modified": "2026-06-11T13:27:44Z",
"published": "2026-06-11T13:27:44Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/security/advisories/GHSA-99f4-grh7-6pcq"
},
{
"type": "PACKAGE",
"url": "https://github.com/grpc/grpc-node"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.10.12"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.11.4"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.12.7"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.13.5"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.14.4"
},
{
"type": "WEB",
"url": "https://github.com/grpc/grpc-node/releases/tag/%40grpc%2Fgrpc-js%401.9.16"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "@grpc/grpc-js: An incoming malformed compressed message can cause a client or server crash"
}
GHSA-99FR-MXGJ-J98P
Vulnerability from github – Published: 2025-11-20 21:30 – Updated: 2025-12-02 03:31HackerOne community member Dao Hoang Anh (yoyomiski) has reported an uncontrolled resource consumption vulnerability in the “userlog-index.php”. An attacker with access to the admin interface could request an arbitrarily large number of items per page, potentially leading to a denial of service
{
"affected": [],
"aliases": [
"CVE-2025-55128"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-11-20T19:16:19Z",
"severity": "MODERATE"
},
"details": "HackerOne community member Dao Hoang Anh (yoyomiski) has reported an uncontrolled resource consumption vulnerability in the \u201cuserlog-index.php\u201d. An attacker with access to the admin interface could request an arbitrarily large number of items per page, potentially leading to a denial of service",
"id": "GHSA-99fr-mxgj-j98p",
"modified": "2025-12-02T03:31:36Z",
"published": "2025-11-20T21:30:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-55128"
},
{
"type": "WEB",
"url": "https://hackerone.com/reports/3413890"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-99GF-96V5-5648
Vulnerability from github – Published: 2023-10-16 09:30 – Updated: 2023-10-16 09:30Denial of Service in GitHub repository gpac/gpac prior to 2.3.0-DEV.
{
"affected": [],
"aliases": [
"CVE-2023-5595"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2023-10-16T09:15:12Z",
"severity": "MODERATE"
},
"details": "Denial of Service in GitHub repository gpac/gpac prior to 2.3.0-DEV.",
"id": "GHSA-99gf-96v5-5648",
"modified": "2023-10-16T09:30:19Z",
"published": "2023-10-16T09:30:19Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-5595"
},
{
"type": "WEB",
"url": "https://github.com/gpac/gpac/commit/7a6f636db3360bb16d18078d51e8c596f31302a1"
},
{
"type": "WEB",
"url": "https://huntr.dev/bounties/0064cf76-ece1-495d-82b4-e4a1bebeb28e"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-99GW-CQ6G-RHMM
Vulnerability from github – Published: 2024-10-15 21:30 – Updated: 2025-03-13 18:32Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: PS). Supported versions that are affected are 8.4.0 and 9.0.1 and prior. Easily exploitable vulnerability allows high privileged attacker with network access via multiple protocols to compromise MySQL Server. Successful attacks of this vulnerability can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of MySQL Server. CVSS 3.1 Base Score 4.9 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H).
{
"affected": [],
"aliases": [
"CVE-2024-21204"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-10-15T20:15:08Z",
"severity": "MODERATE"
},
"details": "Vulnerability in the MySQL Server product of Oracle MySQL (component: Server: PS). Supported versions that are affected are 8.4.0 and 9.0.1 and prior. Easily exploitable vulnerability allows high privileged attacker with network access via multiple protocols to compromise MySQL Server. Successful attacks of this vulnerability can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of MySQL Server. CVSS 3.1 Base Score 4.9 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H).",
"id": "GHSA-99gw-cq6g-rhmm",
"modified": "2025-03-13T18:32:11Z",
"published": "2024-10-15T21:30:38Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-21204"
},
{
"type": "WEB",
"url": "https://security.netapp.com/advisory/ntap-20241101-0009"
},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpuoct2024.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-99H2-3927-3H39
Vulnerability from github – Published: 2024-07-17 00:32 – Updated: 2024-07-17 00:32Vulnerability in the Oracle Database Portable Clusterware component of Oracle Database Server. Supported versions that are affected are 19.3-19.23 and 21.3-21.14. Easily exploitable vulnerability allows unauthenticated attacker with network access via DNS to compromise Oracle Database Portable Clusterware. While the vulnerability is in Oracle Database Portable Clusterware, attacks may significantly impact additional products (scope change). Successful attacks of this vulnerability can result in unauthorized ability to cause a partial denial of service (partial DOS) of Oracle Database Portable Clusterware. CVSS 3.1 Base Score 5.8 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L).
{
"affected": [],
"aliases": [
"CVE-2024-21126"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-07-16T23:15:12Z",
"severity": "MODERATE"
},
"details": "Vulnerability in the Oracle Database Portable Clusterware component of Oracle Database Server. Supported versions that are affected are 19.3-19.23 and 21.3-21.14. Easily exploitable vulnerability allows unauthenticated attacker with network access via DNS to compromise Oracle Database Portable Clusterware. While the vulnerability is in Oracle Database Portable Clusterware, attacks may significantly impact additional products (scope change). Successful attacks of this vulnerability can result in unauthorized ability to cause a partial denial of service (partial DOS) of Oracle Database Portable Clusterware. CVSS 3.1 Base Score 5.8 (Availability impacts). CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L).",
"id": "GHSA-99h2-3927-3h39",
"modified": "2024-07-17T00:32:54Z",
"published": "2024-07-17T00:32:54Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-21126"
},
{
"type": "WEB",
"url": "https://www.oracle.com/security-alerts/cpujul2024.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-99MV-PFX6-V678
Vulnerability from github – Published: 2022-06-23 00:00 – Updated: 2022-07-01 00:01An Uncontrolled Resource Consumption vulnerability in spacewalk-java of SUSE Manager Server 4.1, SUSE Manager Server 4.2 allows remote attackers to easily exhaust available disk resources leading to DoS. This issue affects: SUSE Manager Server 4.1 spacewalk-java versions prior to 4.1.46. SUSE Manager Server 4.2 spacewalk-java versions prior to 4.2.37.
{
"affected": [],
"aliases": [
"CVE-2022-21952"
],
"database_specific": {
"cwe_ids": [
"CWE-306",
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2022-06-22T10:15:00Z",
"severity": "HIGH"
},
"details": "An Uncontrolled Resource Consumption vulnerability in spacewalk-java of SUSE Manager Server 4.1, SUSE Manager Server 4.2 allows remote attackers to easily exhaust available disk resources leading to DoS. This issue affects: SUSE Manager Server 4.1 spacewalk-java versions prior to 4.1.46. SUSE Manager Server 4.2 spacewalk-java versions prior to 4.2.37.",
"id": "GHSA-99mv-pfx6-v678",
"modified": "2022-07-01T00:01:14Z",
"published": "2022-06-23T00:00:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-21952"
},
{
"type": "WEB",
"url": "https://bugzilla.suse.com/show_bug.cgi?id=1199512"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Mitigation
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Mitigation
- Mitigation of resource exhaustion attacks requires that the target system either:
- The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
- The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- recognizes the attack and denies that user further access for a given amount of time, or
- uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed.
Mitigation
Ensure that protocols have specific limits of scale placed on them.
Mitigation
Ensure that all failures in resource allocation place the system into a safe posture.
CAPEC-147: XML Ping of the Death
An attacker initiates a resource depletion attack where a large number of small XML messages are delivered at a sufficiently rapid rate to cause a denial of service or crash of the target. Transactions such as repetitive SOAP transactions can deplete resources faster than a simple flooding attack because of the additional resources used by the SOAP protocol and the resources necessary to process SOAP messages. The transactions used are immaterial as long as they cause resource utilization on the target. In other words, this is a normal flooding attack augmented by using messages that will require extra processing on the target.
CAPEC-227: Sustained Client Engagement
An adversary attempts to deny legitimate users access to a resource by continually engaging a specific resource in an attempt to keep the resource tied up as long as possible. The adversary's primary goal is not to crash or flood the target, which would alert defenders; rather it is to repeatedly perform actions or abuse algorithmic flaws such that a given resource is tied up and not available to a legitimate user. By carefully crafting a requests that keep the resource engaged through what is seemingly benign requests, legitimate users are limited or completely denied access to the resource.
CAPEC-492: Regular Expression Exponential Blowup
An adversary may execute an attack on a program that uses a poor Regular Expression(Regex) implementation by choosing input that results in an extreme situation for the Regex. A typical extreme situation operates at exponential time compared to the input size. This is due to most implementations using a Nondeterministic Finite Automaton(NFA) state machine to be built by the Regex algorithm since NFA allows backtracking and thus more complex regular expressions.