CWE-400
DiscouragedUncontrolled Resource Consumption
Abstraction: Class · Status: Draft
The product does not properly control the allocation and maintenance of a limited resource.
6502 vulnerabilities reference this CWE, most recent first.
GHSA-PJX6-JJ7C-74M7
Vulnerability from github – Published: 2022-05-24 17:22 – Updated: 2022-08-11 00:00A vulnerability has been identified in Opcenter Execution Discrete (All versions < V3.2), Opcenter Execution Foundation (All versions < V3.2), Opcenter Execution Process (All versions < V3.2), Opcenter Intelligence (All versions), Opcenter Quality (All versions < V11.3), Opcenter RD&L (V8.0), SIMATIC IT LMS (All versions), SIMATIC IT Production Suite (All versions), SIMATIC Notifier Server for Windows (All versions), SIMATIC PCS neo (All versions), SIMATIC STEP 7 (TIA Portal) V15 (All versions), SIMATIC STEP 7 (TIA Portal) V16 (All versions < V16 Update 2), SIMOCODE ES (All versions), Soft Starter ES (All versions). Sending multiple specially crafted packets to the affected service could cause a partial remote Denial-of-Service, that would cause the service to restart itself. On some cases the vulnerability could leak random information from the remote service.
{
"affected": [],
"aliases": [
"CVE-2020-7587"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2020-07-14T14:15:00Z",
"severity": "MODERATE"
},
"details": "A vulnerability has been identified in Opcenter Execution Discrete (All versions \u003c V3.2), Opcenter Execution Foundation (All versions \u003c V3.2), Opcenter Execution Process (All versions \u003c V3.2), Opcenter Intelligence (All versions), Opcenter Quality (All versions \u003c V11.3), Opcenter RD\u0026L (V8.0), SIMATIC IT LMS (All versions), SIMATIC IT Production Suite (All versions), SIMATIC Notifier Server for Windows (All versions), SIMATIC PCS neo (All versions), SIMATIC STEP 7 (TIA Portal) V15 (All versions), SIMATIC STEP 7 (TIA Portal) V16 (All versions \u003c V16 Update 2), SIMOCODE ES (All versions), Soft Starter ES (All versions). Sending multiple specially crafted packets to the affected service could cause a partial remote Denial-of-Service, that would cause the service to restart itself. On some cases the vulnerability could leak random information from the remote service.",
"id": "GHSA-pjx6-jj7c-74m7",
"modified": "2022-08-11T00:00:20Z",
"published": "2022-05-24T17:22:55Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2020-7587"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/pdf/ssa-841348.pdf"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-PJXW-22XF-6PWC
Vulnerability from github – Published: 2019-02-07 18:16 – Updated: 2023-09-12 21:05All versions of defaults-deep are vulnerable to prototype pollution. Provided certain input defaults-deep can add or modify properties of the Object prototype. These properties will be present on all objects.
Recommendation
As no patch is currently available for this vulnerability it is our recommendation to select another module that can provide this functionality.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "defaults-deep"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "0.2.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2018-16486"
],
"database_specific": {
"cwe_ids": [
"CWE-345",
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2020-06-16T21:49:31Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "All versions of `defaults-deep` are vulnerable to prototype pollution. Provided certain input `defaults-deep` can add or modify properties of the `Object` prototype. These properties will be present on all objects.\n\n\n## Recommendation\n\nAs no patch is currently available for this vulnerability it is our recommendation to select another module that can provide this functionality.",
"id": "GHSA-pjxw-22xf-6pwc",
"modified": "2023-09-12T21:05:03Z",
"published": "2019-02-07T18:16:38Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2018-16486"
},
{
"type": "WEB",
"url": "https://hackerone.com/reports/380878"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-pjxw-22xf-6pwc"
},
{
"type": "PACKAGE",
"url": "https://github.com/jonschlinkert/defaults-deep"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/778"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Prototype Pollution in defaults-deep"
}
GHSA-PM38-P7H6-V3QF
Vulnerability from github – Published: 2022-05-24 17:21 – Updated: 2022-05-24 17:21An issue was discovered in Mattermost Server before 5.18.0. It allows attackers to cause a denial of service (memory consumption) via a large Slack import.
{
"affected": [],
"aliases": [
"CVE-2019-20845"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2020-06-19T14:15:00Z",
"severity": "MODERATE"
},
"details": "An issue was discovered in Mattermost Server before 5.18.0. It allows attackers to cause a denial of service (memory consumption) via a large Slack import.",
"id": "GHSA-pm38-p7h6-v3qf",
"modified": "2022-05-24T17:21:10Z",
"published": "2022-05-24T17:21:10Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-20845"
},
{
"type": "WEB",
"url": "https://mattermost.com/security-updates"
}
],
"schema_version": "1.4.0",
"severity": []
}
GHSA-PM7W-94QJ-7Q86
Vulnerability from github – Published: 2026-08-11 18:30 – Updated: 2026-08-11 18:30CAI Content Credentials is affected by an Uncontrolled Resource Consumption vulnerability that could lead to application denial-of-service. An attacker could exploit this vulnerability to exhaust system resources, resulting in an application denial-of-service condition. Exploitation of this issue does not require user interaction.
{
"affected": [],
"aliases": [
"CVE-2026-48434"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-11T17:18:00Z",
"severity": "MODERATE"
},
"details": "CAI Content Credentials is affected by an Uncontrolled Resource Consumption vulnerability that could lead to application denial-of-service. An attacker could exploit this vulnerability to exhaust system resources, resulting in an application denial-of-service condition. Exploitation of this issue does not require user interaction.",
"id": "GHSA-pm7w-94qj-7q86",
"modified": "2026-08-11T18:30:57Z",
"published": "2026-08-11T18:30:57Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48434"
},
{
"type": "WEB",
"url": "https://helpx.adobe.com/security/products/content-authenticity-sdk/apsb26-111.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-PM9P-9926-W68M
Vulnerability from github – Published: 2017-12-28 22:52 – Updated: 2021-09-16 18:15ecstatic, a simple static file server middleware, is vulnerable to denial of service. If a payload with a large number of null bytes (%00) is provided by an attacker it can crash ecstatic by running it out of memory.
Results from the original advisory
A payload of 22kB caused a lag of 1 second,
A payload of 35kB caused a lag of 3 seconds,
A payload of 86kB caused the server to crash
Recommendation
Update to version 2.0.0 or later.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "ecstatic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2016-10703"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2020-06-16T21:49:34Z",
"nvd_published_at": "2017-12-14T19:29:00Z",
"severity": "HIGH"
},
"details": "`ecstatic`, a simple static file server middleware, is vulnerable to denial of service. If a payload with a large number of null bytes (`%00`) is provided by an attacker it can crash ecstatic by running it out of memory.\n\n\n[Results from the original advisory](https://www.checkmarx.com/advisories/denial-of-service-dos-vulnerability-in-ecstatic-npm-package/)\n\n```\nA payload of 22kB caused a lag of 1 second,\nA payload of 35kB caused a lag of 3 seconds,\nA payload of 86kB caused the server to crash\n```\n\n\n## Recommendation\n\nUpdate to version 2.0.0 or later.",
"id": "GHSA-pm9p-9926-w68m",
"modified": "2021-09-16T18:15:09Z",
"published": "2017-12-28T22:52:47Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2016-10703"
},
{
"type": "WEB",
"url": "https://github.com/jfhbrook/node-ecstatic/commit/71ce93988ead4b561a8592168c72143907189f01"
},
{
"type": "WEB",
"url": "https://github.com/jfhbrook/node-ecstatic/commit/71ce93988ead4b561a8592168c72143907189f01#diff-b2b5a88fb51675f1aa1065c093dce1ee"
},
{
"type": "WEB",
"url": "https://advisory.checkmarx.net/advisory/CX-2016-4450"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-pm9p-9926-w68m"
},
{
"type": "PACKAGE",
"url": "https://github.com/jfhbrook/node-ecstatic"
},
{
"type": "WEB",
"url": "https://www.checkmarx.com/advisories/denial-of-service-dos-vulnerability-in-ecstatic-npm-package"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/553"
}
],
"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": "Denial of Service in ecstatic"
}
GHSA-PMG9-P9R2-6Q87
Vulnerability from github – Published: 2018-07-24 19:46 – Updated: 2021-01-08 18:20Affected versions of ua-parser are vulnerable to regular expression denial of service when given a specially crafted User-Agent header.
Recommendation
No patch is currently available for this vulnerability.
The best mitigation is currently to avoid using this package, using a different, functionally equivalent package such as useragent.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "ua-parser"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "0.3.5"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2017-16086"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2020-06-16T21:49:36Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "Affected versions of `ua-parser` are vulnerable to regular expression denial of service when given a specially crafted `User-Agent` header.\n\n\n## Recommendation\n\nNo patch is currently available for this vulnerability.\n\nThe best mitigation is currently to avoid using this package, using a different, functionally equivalent package such as [useragent](https://www.npmjs.com/package/useragent).",
"id": "GHSA-pmg9-p9r2-6q87",
"modified": "2021-01-08T18:20:33Z",
"published": "2018-07-24T19:46:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2017-16086"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-pmg9-p9r2-6q87"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/316"
}
],
"schema_version": "1.4.0",
"severity": [],
"summary": "ReDoS via long UserAgent header in ua-parser"
}
GHSA-PMH6-CQ54-943M
Vulnerability from github – Published: 2023-01-05 03:30 – Updated: 2025-04-07 21:31WordPress through 6.1.1 depends on unpredictable client visits to cause wp-cron.php execution and the resulting security updates, and the source code describes "the scenario where a site may not receive enough visits to execute scheduled tasks in a timely manner," but neither the installation guide nor the security guide mentions this default behavior, or alerts the user about security risks on installations with very few visits.
{
"affected": [],
"aliases": [
"CVE-2023-22622"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2023-01-05T02:15:00Z",
"severity": "HIGH"
},
"details": "WordPress through 6.1.1 depends on unpredictable client visits to cause wp-cron.php execution and the resulting security updates, and the source code describes \"the scenario where a site may not receive enough visits to execute scheduled tasks in a timely manner,\" but neither the installation guide nor the security guide mentions this default behavior, or alerts the user about security risks on installations with very few visits.",
"id": "GHSA-pmh6-cq54-943m",
"modified": "2025-04-07T21:31:37Z",
"published": "2023-01-05T03:30:36Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-22622"
},
{
"type": "WEB",
"url": "https://developer.wordpress.org/plugins/cron"
},
{
"type": "WEB",
"url": "https://github.com/WordPress/WordPress/blob/dca7b5204b5fea54e6d1774689777b359a9222ab/wp-cron.php#L5-L8"
},
{
"type": "WEB",
"url": "https://medium.com/%40thecpanelguy/the-nightmare-that-is-wpcron-php-ae31c1d3ae30"
},
{
"type": "WEB",
"url": "https://medium.com/@thecpanelguy/the-nightmare-that-is-wpcron-php-ae31c1d3ae30"
},
{
"type": "WEB",
"url": "https://patchstack.com/articles/solving-unpredictable-wp-cron-problems-addressing-cve-2023-22622"
},
{
"type": "WEB",
"url": "https://wordpress.org/about/security"
},
{
"type": "WEB",
"url": "https://wordpress.org/support/article/how-to-install-wordpress"
},
{
"type": "WEB",
"url": "https://www.tenable.com/plugins/was/113449"
}
],
"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-PMP2-F627-C94J
Vulnerability from github – Published: 2022-11-04 19:01 – Updated: 2022-11-07 19:00A vulnerability in a feature that monitors RADIUS requests on Cisco Identity Services Engine (ISE) Software could allow an unauthenticated, remote attacker to negatively affect the performance of an affected device. This vulnerability is due to insufficient management of system resources. An attacker could exploit this vulnerability by taking actions that cause Cisco ISE Software to receive specific RADIUS traffic. A successful and sustained exploit of this vulnerability could allow the attacker to cause reduced performance of the affected device, resulting in significant delays to RADIUS authentications. There are workarounds that address this vulnerability.
{
"affected": [],
"aliases": [
"CVE-2022-20937"
],
"database_specific": {
"cwe_ids": [
"CWE-400",
"CWE-410"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2022-11-04T18:15:00Z",
"severity": "MODERATE"
},
"details": "A vulnerability in a feature that monitors RADIUS requests on Cisco Identity Services Engine (ISE) Software could allow an unauthenticated, remote attacker to negatively affect the performance of an affected device. This vulnerability is due to insufficient management of system resources. An attacker could exploit this vulnerability by taking actions that cause Cisco ISE Software to receive specific RADIUS traffic. A successful and sustained exploit of this vulnerability could allow the attacker to cause reduced performance of the affected device, resulting in significant delays to RADIUS authentications. There are workarounds that address this vulnerability.",
"id": "GHSA-pmp2-f627-c94j",
"modified": "2022-11-07T19:00:17Z",
"published": "2022-11-04T19:01:09Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-20937"
},
{
"type": "WEB",
"url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ise-sec-atk-dos-zw5RCUYp"
},
{
"type": "WEB",
"url": "https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ise-sec-atk-dos-zw5RCUYp"
}
],
"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:L",
"type": "CVSS_V3"
}
]
}
GHSA-PMQ5-6568-8497
Vulnerability from github – Published: 2026-08-19 21:30 – Updated: 2026-08-19 21:30IBM AIX 7.2, and 7.3 and IBM PowerVM VIOS 4.1 could allow a remote attacker to cause a denial of service due to improper handling of a missing SSL client certificate.
{
"affected": [],
"aliases": [
"CVE-2026-16837"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-19T20:17:04Z",
"severity": "HIGH"
},
"details": "IBM AIX 7.2, and 7.3 and IBM PowerVM VIOS 4.1 could allow a remote attacker to cause a denial of service due to improper handling of a missing SSL client certificate.",
"id": "GHSA-pmq5-6568-8497",
"modified": "2026-08-19T21:30:34Z",
"published": "2026-08-19T21:30:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-16837"
},
{
"type": "WEB",
"url": "https://www.ibm.com/support/pages/node/7283858"
}
],
"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-PMQC-57G8-C22C
Vulnerability from github – Published: 2026-06-01 06:30 – Updated: 2026-07-28 19:46A security vulnerability has been detected in NousResearch hermes-agent up to 2026.4.30. This vulnerability affects the function _handle_webhook_request of the file gateway/platforms/feishu.py of the component Webhook Endpoint. Such manipulation leads to resource consumption. The attack can be launched remotely. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "hermes-agent"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "0.19.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-10224"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-28T19:46:01Z",
"nvd_published_at": "2026-06-01T06:16:38Z",
"severity": "MODERATE"
},
"details": "A security vulnerability has been detected in NousResearch hermes-agent up to 2026.4.30. This vulnerability affects the function _handle_webhook_request of the file gateway/platforms/feishu.py of the component Webhook Endpoint. Such manipulation leads to resource consumption. The attack can be launched remotely. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.",
"id": "GHSA-pmqc-57g8-c22c",
"modified": "2026-07-28T19:46:01Z",
"published": "2026-06-01T06:30:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-10224"
},
{
"type": "WEB",
"url": "https://github.com/NousResearch/hermes-agent/issues/29154"
},
{
"type": "WEB",
"url": "https://github.com/NousResearch/hermes-agent/pull/73406"
},
{
"type": "WEB",
"url": "https://gist.github.com/YLChen-007/0304e313d811f187ade93d3b01de0f87"
},
{
"type": "PACKAGE",
"url": "https://github.com/NousResearch/hermes-agent"
},
{
"type": "WEB",
"url": "https://vuldb.com/cve/CVE-2026-10224"
},
{
"type": "WEB",
"url": "https://vuldb.com/submit/822022"
},
{
"type": "WEB",
"url": "https://vuldb.com/vuln/367503"
},
{
"type": "WEB",
"url": "https://vuldb.com/vuln/367503/cti"
}
],
"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:L",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P",
"type": "CVSS_V4"
}
],
"summary": "hermes-agent has an Uncontrolled Resource Consumption issue"
}
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.