CWE-400
DiscouragedUncontrolled Resource Consumption
Abstraction: Class · Status: Draft
The product does not properly control the allocation and maintenance of a limited resource.
6391 vulnerabilities reference this CWE, most recent first.
GHSA-FVC2-9Q3J-5CG7
Vulnerability from github – Published: 2022-05-05 00:28 – Updated: 2022-05-05 00:28cipso_v4_validate in include/net/cipso_ipv4.h in the Linux kernel before 3.11.7, when CONFIG_NETLABEL is disabled, allows attackers to cause a denial of service (infinite loop and crash), as demonstrated by icmpsic, a different vulnerability than CVE-2013-0310.
{
"affected": [],
"aliases": [
"CVE-2013-7470"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2019-04-23T03:29:00Z",
"severity": "HIGH"
},
"details": "cipso_v4_validate in include/net/cipso_ipv4.h in the Linux kernel before 3.11.7, when CONFIG_NETLABEL is disabled, allows attackers to cause a denial of service (infinite loop and crash), as demonstrated by icmpsic, a different vulnerability than CVE-2013-0310.",
"id": "GHSA-fvc2-9q3j-5cg7",
"modified": "2022-05-05T00:28:53Z",
"published": "2022-05-05T00:28:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2013-7470"
},
{
"type": "WEB",
"url": "https://github.com/torvalds/linux/commit/f2e5ddcc0d12f9c4c7b254358ad245c9dddce13b"
},
{
"type": "WEB",
"url": "https://cdn.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.11.7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f2e5ddcc0d12f9c4c7b254358ad245c9dddce13b"
},
{
"type": "WEB",
"url": "https://support.f5.com/csp/article/K21914362"
},
{
"type": "WEB",
"url": "https://www.arista.com/en/support/advisories-notices/security-advisories/7098-security-advisory-40"
}
],
"schema_version": "1.4.0",
"severity": []
}
GHSA-FVCW-V2MX-PFQ9
Vulnerability from github – Published: 2023-09-12 18:30 – Updated: 2024-04-04 07:38Windows TCP/IP Denial of Service Vulnerability
{
"affected": [],
"aliases": [
"CVE-2023-38149"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2023-09-12T17:15:18Z",
"severity": "HIGH"
},
"details": "Windows TCP/IP Denial of Service Vulnerability",
"id": "GHSA-fvcw-v2mx-pfq9",
"modified": "2024-04-04T07:38:09Z",
"published": "2023-09-12T18:30:22Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-38149"
},
{
"type": "WEB",
"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-38149"
}
],
"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-FVH4-7PMW-84HM
Vulnerability from github – Published: 2025-07-21 12:30 – Updated: 2025-11-03 21:34A high privileged remote attacker can exhaust critical system resources by sending specifically crafted POST requests to the send-mail action in fast succession.
{
"affected": [],
"aliases": [
"CVE-2025-41677"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-07-21T10:15:24Z",
"severity": "MODERATE"
},
"details": "A high privileged remote attacker can exhaust critical system resources by sending specifically crafted POST requests to the send-mail action in fast succession.",
"id": "GHSA-fvh4-7pmw-84hm",
"modified": "2025-11-03T21:34:09Z",
"published": "2025-07-21T12:30:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-41677"
},
{
"type": "WEB",
"url": "https://certvde.com/de/advisories/VDE-2025-058"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2025/Jul/38"
}
],
"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-FVMR-RJJ2-5PQ8
Vulnerability from github – Published: 2026-07-29 09:31 – Updated: 2026-07-29 09:31Apache Traffic Server can be crashed or driven to resource exhaustion by abusive HTTP/2 framing and flow-control.
This issue affects Apache Traffic Server: from 8.0.0 through 8.1.9, from 9.0.0 through 9.2.14, from 10.0.0 through 10.1.3.
Users are recommended to upgrade to version 9.2.15 or 10.1.4, which fix the issue.
{
"affected": [],
"aliases": [
"CVE-2026-58151"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-29T09:16:29Z",
"severity": "HIGH"
},
"details": "Apache Traffic Server can be crashed or driven to resource exhaustion by abusive HTTP/2 framing and flow-control.\n\nThis issue affects Apache Traffic Server: from 8.0.0 through 8.1.9, from 9.0.0 through 9.2.14, from 10.0.0 through 10.1.3.\n\nUsers are recommended to upgrade to version 9.2.15 or 10.1.4, which fix the issue.",
"id": "GHSA-fvmr-rjj2-5pq8",
"modified": "2026-07-29T09:31:29Z",
"published": "2026-07-29T09:31:29Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-58151"
},
{
"type": "WEB",
"url": "https://lists.apache.org/thread/5prl9glcm9g2swnq9hqxvnokylm1gr6d"
}
],
"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"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"type": "CVSS_V4"
}
]
}
GHSA-FVMW-88R5-VRP4
Vulnerability from github – Published: 2022-05-13 01:34 – Updated: 2022-05-13 01:34A vulnerability in the Bulk Administration Tool (BAT) for Cisco Unity Connection could allow an authenticated, remote attacker to cause high disk utilization, resulting in a denial of service (DoS) condition. The vulnerability exists because the affected software does not restrict the maximum size of certain files that can be written to disk. An attacker who has valid administrator credentials for an affected system could exploit this vulnerability by sending a crafted, remote connection request to an affected system. A successful exploit could allow the attacker to write a file that consumes most of the available disk space on the system, causing application functions to operate abnormally and leading to a DoS condition.
{
"affected": [],
"aliases": [
"CVE-2018-15396"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2018-10-05T14:29:00Z",
"severity": "MODERATE"
},
"details": "A vulnerability in the Bulk Administration Tool (BAT) for Cisco Unity Connection could allow an authenticated, remote attacker to cause high disk utilization, resulting in a denial of service (DoS) condition. The vulnerability exists because the affected software does not restrict the maximum size of certain files that can be written to disk. An attacker who has valid administrator credentials for an affected system could exploit this vulnerability by sending a crafted, remote connection request to an affected system. A successful exploit could allow the attacker to write a file that consumes most of the available disk space on the system, causing application functions to operate abnormally and leading to a DoS condition.",
"id": "GHSA-fvmw-88r5-vrp4",
"modified": "2022-05-13T01:34:21Z",
"published": "2022-05-13T01:34:21Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2018-15396"
},
{
"type": "WEB",
"url": "https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181003-unity-dos"
},
{
"type": "WEB",
"url": "http://www.securitytracker.com/id/1041782"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-FVMX-5P62-PXM8
Vulnerability from github – Published: 2024-09-17 00:31 – Updated: 2025-11-04 18:31An out-of-bounds access issue was addressed with improved bounds checking. This issue is fixed in macOS Ventura 13.7, iOS 17.7 and iPadOS 17.7, visionOS 2, watchOS 11, macOS Sequoia 15, iOS 18 and iPadOS 18, macOS Sonoma 14.7, tvOS 18. Processing an image may lead to a denial-of-service.
{
"affected": [],
"aliases": [
"CVE-2024-44176"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-09-17T00:15:51Z",
"severity": "MODERATE"
},
"details": "An out-of-bounds access issue was addressed with improved bounds checking. This issue is fixed in macOS Ventura 13.7, iOS 17.7 and iPadOS 17.7, visionOS 2, watchOS 11, macOS Sequoia 15, iOS 18 and iPadOS 18, macOS Sonoma 14.7, tvOS 18. Processing an image may lead to a denial-of-service.",
"id": "GHSA-fvmx-5p62-pxm8",
"modified": "2025-11-04T18:31:24Z",
"published": "2024-09-17T00:31:06Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-44176"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121234"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121238"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121240"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121246"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121247"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121248"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121249"
},
{
"type": "WEB",
"url": "https://support.apple.com/en-us/121250"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2024/Sep/32"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2024/Sep/33"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2024/Sep/36"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2024/Sep/40"
},
{
"type": "WEB",
"url": "http://seclists.org/fulldisclosure/2024/Sep/41"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-FVQJ-2F9F-F8H7
Vulnerability from github – Published: 2026-02-19 00:30 – Updated: 2026-02-19 00:30Bematech (formerly Logic Controls, now Elgin) MP-4200 TH printer contains a denial of service vulnerability in the admin configuration page. Remote attackers can send crafted POST requests with malformed 'admin' and 'person' parameters to crash the printer's web service, causing a denial of service condition.
{
"affected": [],
"aliases": [
"CVE-2019-25401"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-02-18T22:16:23Z",
"severity": "HIGH"
},
"details": "Bematech (formerly Logic Controls, now Elgin) MP-4200 TH printer contains a denial of service vulnerability in the admin configuration page. Remote attackers can send crafted POST requests with malformed \u0027admin\u0027 and \u0027person\u0027 parameters to crash the printer\u0027s web service, causing a denial of service condition.",
"id": "GHSA-fvqj-2f9f-f8h7",
"modified": "2026-02-19T00:30:29Z",
"published": "2026-02-19T00:30:29Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2019-25401"
},
{
"type": "WEB",
"url": "https://web.archive.org/web/20180814065516/https://www.bematech.com.br"
},
{
"type": "WEB",
"url": "https://www.exploit-db.com/exploits/47648"
},
{
"type": "WEB",
"url": "https://www.legacyglobal.com/products/bematech-formerly-logic-controls-mp-4200-thermal-receipt-printer/?srsltid=AfmBOor3LXakwJp10bE_8n8YIBKrFPFGFc5DKrxdMGChGQ-Y24i8MVQa"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/bematech-printer-mp-th-denial-of-service"
}
],
"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"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"type": "CVSS_V4"
}
]
}
GHSA-FVR3-V8H9-3CWW
Vulnerability from github – Published: 2025-11-10 21:30 – Updated: 2025-11-12 21:31In Open5GS 2.7.6, AMF crashes when receiving an abnormal NGSetupRequest message, resulting in denial of service.
{
"affected": [],
"aliases": [
"CVE-2025-63288"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-11-10T19:15:57Z",
"severity": "HIGH"
},
"details": "In Open5GS 2.7.6, AMF crashes when receiving an abnormal NGSetupRequest message, resulting in denial of service.",
"id": "GHSA-fvr3-v8h9-3cww",
"modified": "2025-11-12T21:31:06Z",
"published": "2025-11-10T21:30:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-63288"
},
{
"type": "WEB",
"url": "https://github.com/open5gs/open5gs/issues/4087"
},
{
"type": "WEB",
"url": "https://github.com/open5gs/open5gs/commit/be765fe2b03e350836272eee5afb3931bdfb86d5"
}
],
"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-FVRX-R5JQ-295Q
Vulnerability from github – Published: 2026-10-01 18:32 – Updated: 2026-10-01 18:32The Smile parser in FasterXML jackson-dataformats-binary never invokes StreamReadConstraints.validateNameLength() when decoding JSON object property names, so the maxNameLength limit is not enforced for this format. SmileParser._handleLongFieldName() grows its internal name buffer through an unconstrained _growArrayTo() call and performs no length validation. An attacker who can have a Smile document parsed may therefore embed a single property name of unbounded length; the parser buffers the whole name in memory before returning it, whatever maxNameLength is configured to. Because StreamReadConstraints.maxDocumentLength is also disabled by default, nothing else bounds the name under default settings, so the only limits are the attacker's upload capacity and available heap, leading to memory exhaustion and denial of service. No privileges beyond the ability to submit data to a parsing endpoint are required, and exploitation needs only that the bytes reach SmileFactory parsing, directly or through an ObjectMapper configured with the Smile module. jackson-core's own JSON parsers enforce maxNameLength incrementally during name decoding; this gap is specific to the binary formats. maxNameLength and validateNameLength were introduced in jackson-core 2.16.0, so releases before 2.16.0 do not contain the constraint that is left unenforced. This issue is tracked together with the CBOR parser defect in the same vendor advisory, GHSA-3v8f-v6vx-fmrm, which covers both binary formats. The Smile parser defect (jackson-dataformats-binary issue #726) is CVE-2026-68496; the CBOR parser defect (issue #725) is assigned CVE-2026-68495.
{
"affected": [],
"aliases": [
"CVE-2026-68496"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-01T18:17:27Z",
"severity": "HIGH"
},
"details": "The Smile parser in FasterXML jackson-dataformats-binary never invokes StreamReadConstraints.validateNameLength() when decoding JSON object property names, so the maxNameLength limit is not enforced for this format. SmileParser._handleLongFieldName() grows its internal name buffer through an unconstrained _growArrayTo() call and performs no length validation. An attacker who can have a Smile document parsed may therefore embed a single property name of unbounded length; the parser buffers the whole name in memory before returning it, whatever maxNameLength is configured to. Because StreamReadConstraints.maxDocumentLength is also disabled by default, nothing else bounds the name under default settings, so the only limits are the attacker\u0027s upload capacity and available heap, leading to memory exhaustion and denial of service. No privileges beyond the ability to submit data to a parsing endpoint are required, and exploitation needs only that the bytes reach SmileFactory parsing, directly or through an ObjectMapper configured with the Smile module. jackson-core\u0027s own JSON parsers enforce maxNameLength incrementally during name decoding; this gap is specific to the binary formats. maxNameLength and validateNameLength were introduced in jackson-core 2.16.0, so releases before 2.16.0 do not contain the constraint that is left unenforced. This issue is tracked together with the CBOR parser defect in the same vendor advisory, GHSA-3v8f-v6vx-fmrm, which covers both binary formats. The Smile parser defect (jackson-dataformats-binary issue #726) is CVE-2026-68496; the CBOR parser defect (issue #725) is assigned CVE-2026-68495.",
"id": "GHSA-fvrx-r5jq-295q",
"modified": "2026-10-01T18:32:48Z",
"published": "2026-10-01T18:32:48Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/FasterXML/jackson-dataformats-binary/security/advisories/GHSA-3v8f-v6vx-fmrm"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-68496"
},
{
"type": "WEB",
"url": "https://github.com/FasterXML/jackson-dataformats-binary/issues/726"
},
{
"type": "WEB",
"url": "https://github.com/FasterXML/jackson-dataformats-binary/blob/2.18/release-notes/VERSION-2.x"
},
{
"type": "WEB",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-68495"
}
],
"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-FVWR-H9XH-M6WC
Vulnerability from github – Published: 2020-09-03 20:33 – Updated: 2020-08-31 18:49Versions of @commercial/subtext prior to 5.1.1 are vulnerable to Denial of Service (DoS). The package fails to enforce the maxBytes configuration for payloads with chunked encoding that are written to the file system. This allows attackers to send requests with arbitrary payload sizes, which may exhaust system resources leading to Denial of Service.
Recommendation
Upgrade to version 5.1.1 or later.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "@commercial/subtext"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "5.1.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:49:40Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "Versions of `@commercial/subtext` prior to 5.1.1 are vulnerable to Denial of Service (DoS). The package fails to enforce the `maxBytes` configuration for payloads with chunked encoding that are written to the file system. This allows attackers to send requests with arbitrary payload sizes, which may exhaust system resources leading to Denial of Service.\n\n\n## Recommendation\n\nUpgrade to version 5.1.1 or later.",
"id": "GHSA-fvwr-h9xh-m6wc",
"modified": "2020-08-31T18:49:40Z",
"published": "2020-09-03T20:33:17Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/hapijs/subtext/issues/72"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/1166"
}
],
"schema_version": "1.4.0",
"severity": [],
"summary": "Denial of Service in @commercial/subtext"
}
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.