Common Weakness Enumeration

CWE-400

Discouraged

Uncontrolled Resource Consumption

Abstraction: Class · Status: Draft

The product does not properly control the allocation and maintenance of a limited resource.

5412 vulnerabilities reference this CWE, most recent first.

GHSA-VP43-WPFX-V79M

Vulnerability from github – Published: 2024-06-25 21:31 – Updated: 2024-06-25 21:31
VLAI
Details

In WhatsUp Gold versions released before 2023.1.3, an unauthenticated Denial of Service

vulnerability was identified. An unauthenticated attacker can put the application into the SetAdminPassword installation step, which renders the application non-accessible.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2024-5013"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-06-25T21:16:00Z",
    "severity": "HIGH"
  },
  "details": "In WhatsUp Gold versions released before 2023.1.3,\u00a0an unauthenticated Denial of Service \n\nvulnerability was identified.\u00a0An unauthenticated attacker can put the application into the SetAdminPassword installation step, which renders the application non-accessible.",
  "id": "GHSA-vp43-wpfx-v79m",
  "modified": "2024-06-25T21:31:17Z",
  "published": "2024-06-25T21:31:17Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-5013"
    },
    {
      "type": "WEB",
      "url": "https://community.progress.com/s/article/WhatsUp-Gold-Security-Bulletin-June-2024"
    },
    {
      "type": "WEB",
      "url": "https://www.progress.com/network-monitoring"
    }
  ],
  "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-VP56-6G26-6827

Vulnerability from github – Published: 2022-08-02 00:00 – Updated: 2022-08-04 17:37
VLAI
Summary
node-fetch Inefficient Regular Expression Complexity
Details

node-fetch is a light-weight module that brings window.fetch to node.js.

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) in the isOriginPotentiallyTrustworthy() function in referrer.js, when processing a URL string with alternating letters and periods, such as 'http://' + 'a.a.'.repeat(i) + 'a'.

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "node-fetch"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.2.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2022-2596"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2022-08-04T17:37:24Z",
    "nvd_published_at": "2022-08-01T15:15:00Z",
    "severity": "MODERATE"
  },
  "details": "[node-fetch](https://www.npmjs.com/package/node-fetch) is a light-weight module that brings window.fetch to node.js.\n\nAffected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) in the `isOriginPotentiallyTrustworthy()` function in `referrer.js`, when processing a URL string with alternating letters and periods, such as `\u0027http://\u0027 + \u0027a.a.\u0027.repeat(i) + \u0027a\u0027`.",
  "id": "GHSA-vp56-6g26-6827",
  "modified": "2022-08-04T17:37:24Z",
  "published": "2022-08-02T00:00:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2022-2596"
    },
    {
      "type": "WEB",
      "url": "https://github.com/node-fetch/node-fetch/pull/1611"
    },
    {
      "type": "WEB",
      "url": "https://github.com/node-fetch/node-fetch/commit/28802387292baee467e042e168d92597b5bbbe3d"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/node-fetch/node-fetch"
    },
    {
      "type": "WEB",
      "url": "https://github.com/node-fetch/node-fetch/releases/tag/v3.2.10"
    },
    {
      "type": "WEB",
      "url": "https://huntr.dev/bounties/a7e6a136-0a4b-46c4-ad20-802f1dd60bf7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "node-fetch Inefficient Regular Expression Complexity "
}

GHSA-VP77-FQQP-79J8

Vulnerability from github – Published: 2021-04-13 15:20 – Updated: 2021-03-22 22:39
VLAI
Summary
Prototype Pollution in decal
Details

This affects all versions of package decal. The vulnerability is in the set function.

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "decal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "2.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2020-28449"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-03-22T22:39:06Z",
    "nvd_published_at": "2021-02-04T15:15:00Z",
    "severity": "HIGH"
  },
  "details": "This affects all versions of package decal. The vulnerability is in the set function.",
  "id": "GHSA-vp77-fqqp-79j8",
  "modified": "2021-03-22T22:39:06Z",
  "published": "2021-04-13T15:20:27Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2020-28449"
    },
    {
      "type": "WEB",
      "url": "https://github.com/gigafied/decal.js/blob/master/src/utils/set.js%23L45-L73"
    },
    {
      "type": "WEB",
      "url": "https://snyk.io/vuln/SNYK-JS-DECAL-1051007"
    },
    {
      "type": "WEB",
      "url": "https://www.npmjs.com/package/decal"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Prototype Pollution in decal"
}

GHSA-VP7J-5755-6R5Q

Vulnerability from github – Published: 2022-05-14 00:55 – Updated: 2022-05-14 00:55
VLAI
Details

Endless recursion exists in xkbcomp/expr.c in xkbcommon and libxkbcommon before 0.8.1, which could be used by local attackers to crash xkbcommon users by supplying a crafted keymap file that triggers boolean negation.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2018-15853"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2018-08-25T21:29:00Z",
    "severity": "MODERATE"
  },
  "details": "Endless recursion exists in xkbcomp/expr.c in xkbcommon and libxkbcommon before 0.8.1, which could be used by local attackers to crash xkbcommon users by supplying a crafted keymap file that triggers boolean negation.",
  "id": "GHSA-vp7j-5755-6r5q",
  "modified": "2022-05-14T00:55:01Z",
  "published": "2022-05-14T00:55:01Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2018-15853"
    },
    {
      "type": "WEB",
      "url": "https://github.com/xkbcommon/libxkbcommon/commit/1f9d1248c07cda8aaff762429c0dce146de8632a"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2019:2079"
    },
    {
      "type": "WEB",
      "url": "https://lists.freedesktop.org/archives/wayland-devel/2018-August/039232.html"
    },
    {
      "type": "WEB",
      "url": "https://security.gentoo.org/glsa/201810-05"
    },
    {
      "type": "WEB",
      "url": "https://usn.ubuntu.com/3786-1"
    },
    {
      "type": "WEB",
      "url": "https://usn.ubuntu.com/3786-2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

GHSA-VP98-W2P3-MV35

Vulnerability from github – Published: 2023-03-10 15:30 – Updated: 2025-09-02 22:25
VLAI
Summary
Apache Log4j 1.x (EOL) allows Denial of Service (DoS)
Details

** UNSUPPORTED WHEN ASSIGNED ** When using the Chainsaw or SocketAppender components with Log4j 1.x on JRE less than 1.7, an attacker that manages to cause a logging entry involving a specially-crafted (ie deeply nested) hashmap or hashtable (depending on which logging component is in use) to be processed could exhaust the available memory in the virtual machine and achieve Denial of Service when the object is deserialized. This issue affects Apache Log4j before 2. Affected users are recommended to update to Log4j 2.x. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.apache.logging.log4j:log4j-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.4"
            },
            {
              "fixed": "2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "log4j:log4j"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.4"
            },
            {
              "fixed": "2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-26464"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-502"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2023-03-10T23:48:32Z",
    "nvd_published_at": "2023-03-10T14:15:00Z",
    "severity": "HIGH"
  },
  "details": "** UNSUPPORTED WHEN ASSIGNED ** When using the Chainsaw or SocketAppender components with Log4j 1.x on JRE less than 1.7, an attacker that manages to cause a logging entry involving a specially-crafted (ie deeply nested) hashmap or hashtable (depending on which logging component is in use) to be processed could exhaust the available memory in the virtual machine and achieve Denial of Service when the object is deserialized. This issue affects Apache Log4j before 2. Affected users are recommended to update to Log4j 2.x. NOTE: This vulnerability only affects products that are no longer supported by the maintainer.",
  "id": "GHSA-vp98-w2p3-mv35",
  "modified": "2025-09-02T22:25:25Z",
  "published": "2023-03-10T15:30:43Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-26464"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/apache/logging-log4j2"
    },
    {
      "type": "WEB",
      "url": "https://lists.apache.org/thread/wkx6grrcjkh86crr49p4blc1v1nflj3t"
    },
    {
      "type": "WEB",
      "url": "https://security.netapp.com/advisory/ntap-20230505-0008"
    }
  ],
  "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": "Apache Log4j 1.x (EOL) allows Denial of Service (DoS)"
}

GHSA-VPC9-MJHW-R32H

Vulnerability from github – Published: 2022-10-01 00:00 – Updated: 2022-10-04 00:00
VLAI
Details

An issue was discovered in Xpdf 4.04. There is a crash in gfseek(_IO_FILE*, long, int) in goo/gfile.cc.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2022-41842"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-787"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2022-09-30T05:15:00Z",
    "severity": "MODERATE"
  },
  "details": "An issue was discovered in Xpdf 4.04. There is a crash in gfseek(_IO_FILE*, long, int) in goo/gfile.cc.",
  "id": "GHSA-vpc9-mjhw-r32h",
  "modified": "2022-10-04T00:00:19Z",
  "published": "2022-10-01T00:00:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2022-41842"
    },
    {
      "type": "WEB",
      "url": "https://forum.xpdfreader.com/viewtopic.php?f=1\u0026t=42340\u0026p=43928\u0026hilit=gfseek#p43928"
    },
    {
      "type": "WEB",
      "url": "http://www.xpdfreader.com/download.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

GHSA-VPF7-R2FV-75M9

Vulnerability from github – Published: 2023-05-05 02:19 – Updated: 2024-05-08 13:46
VLAI
Summary
Uncontrolled Resource Consumption in OPC UA .NET Standard Reference Server
Details

This security update resolves a vulnerability in the OPC UA .NET Standard Reference Server that allows remote attackers to send malicious requests that consume all memory available to the server.

https://files.opcfoundation.org/SecurityBulletins/OPC%20Foundation%20Security%20Bulletin%20CVE-2023-27321.pdf

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "OPCFoundation.NetStandard.Opc.Ua.Server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.371.86"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-27321"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2023-05-05T02:19:39Z",
    "nvd_published_at": "2024-05-07T23:15:15Z",
    "severity": "HIGH"
  },
  "details": "This security update resolves a vulnerability in the OPC UA .NET Standard Reference Server that allows\nremote attackers to send malicious requests that consume all memory available to the server.\n\nhttps://files.opcfoundation.org/SecurityBulletins/OPC%20Foundation%20Security%20Bulletin%20CVE-2023-27321.pdf",
  "id": "GHSA-vpf7-r2fv-75m9",
  "modified": "2024-05-08T13:46:55Z",
  "published": "2023-05-05T02:19:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/OPCFoundation/UA-.NETStandard/security/advisories/GHSA-vpf7-r2fv-75m9"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-27321"
    },
    {
      "type": "WEB",
      "url": "https://files.opcfoundation.org/SecurityBulletins/OPC%20Foundation%20Security%20Bulletin%20CVE-2023-27321.pdf"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/OPCFoundation/UA-.NETStandard"
    },
    {
      "type": "WEB",
      "url": "https://www.zerodayinitiative.com/advisories/ZDI-23-548"
    }
  ],
  "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": "Uncontrolled Resource Consumption in OPC UA .NET Standard Reference Server"
}

GHSA-VPG6-7CCH-GQ2J

Vulnerability from github – Published: 2025-03-20 12:32 – Updated: 2025-03-20 12:32
VLAI
Details

A Denial of Service (DoS) vulnerability exists in multiple file upload endpoints of parisneo/lollms-webui version V12 (Strawberry). The vulnerability can be exploited remotely via Cross-Site Request Forgery (CSRF). Despite CSRF protection preventing file uploads, the application still processes multipart boundaries, leading to resource exhaustion. By appending additional characters to the multipart boundary, an attacker can cause the server to parse each byte of the boundary, ultimately leading to service unavailability. This vulnerability is present in the /upload_avatar, /upload_app, and /upload_logo endpoints.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2024-8736"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-352",
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-03-20T10:15:43Z",
    "severity": "HIGH"
  },
  "details": "A Denial of Service (DoS) vulnerability exists in multiple file upload endpoints of parisneo/lollms-webui version V12 (Strawberry). The vulnerability can be exploited remotely via Cross-Site Request Forgery (CSRF). Despite CSRF protection preventing file uploads, the application still processes multipart boundaries, leading to resource exhaustion. By appending additional characters to the multipart boundary, an attacker can cause the server to parse each byte of the boundary, ultimately leading to service unavailability. This vulnerability is present in the `/upload_avatar`, `/upload_app`, and `/upload_logo` endpoints.",
  "id": "GHSA-vpg6-7cch-gq2j",
  "modified": "2025-03-20T12:32:48Z",
  "published": "2025-03-20T12:32:48Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-8736"
    },
    {
      "type": "WEB",
      "url": "https://huntr.com/bounties/935dbc03-1b43-4dbb-b6cd-1aa95a789d4f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H",
      "type": "CVSS_V3"
    }
  ]
}

GHSA-VPHR-3984-5C8W

Vulnerability from github – Published: 2025-12-29 18:30 – Updated: 2025-12-30 18:30
VLAI
Details

An issue was discovered in function d_discriminator in file cp-demangle.c in BinUtils 2.26 allows attackers to cause a denial of service via crafted PE file.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2025-66863"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-12-29T17:15:46Z",
    "severity": "HIGH"
  },
  "details": "An issue was discovered in function d_discriminator in file cp-demangle.c in BinUtils 2.26 allows attackers to cause a denial of service via crafted PE file.",
  "id": "GHSA-vphr-3984-5c8w",
  "modified": "2025-12-30T18:30:16Z",
  "published": "2025-12-29T18:30:55Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-66863"
    },
    {
      "type": "WEB",
      "url": "https://github.com/caozhzh/CRGF-Vul/blob/main/cxxfilt/crash2.md"
    }
  ],
  "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-VPPX-25HC-F892

Vulnerability from github – Published: 2026-05-27 15:33 – Updated: 2026-05-27 15:33
VLAI
Details

IBM Langflow OSS 1.0.0 through 1.9.0 could allow a denial of service due to uncontrolled resource consumption.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2026-7528"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-27T14:17:35Z",
    "severity": "HIGH"
  },
  "details": "IBM Langflow OSS 1.0.0 through 1.9.0 could allow a denial of service due to uncontrolled resource consumption.",
  "id": "GHSA-vppx-25hc-f892",
  "modified": "2026-05-27T15:33:25Z",
  "published": "2026-05-27T15:33:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-7528"
    },
    {
      "type": "WEB",
      "url": "https://www.ibm.com/support/pages/node/7273427"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

Mitigation
Architecture and Design

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
Architecture and Design
  • 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
Architecture and Design

Ensure that protocols have specific limits of scale placed on them.

Mitigation
Implementation

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.