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.

5570 vulnerabilities reference this CWE, most recent first.

GHSA-67P8-JRM8-G765

Vulnerability from github – Published: 2024-06-25 21:31 – Updated: 2024-09-07 00:31
VLAI
Details

In WhatsUp Gold versions released before 2023.1.3, an uncontrolled resource consumption vulnerability exists. A specially crafted unauthenticated HTTP request to the TestController Chart functionality can lead to denial of service.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2024-5011"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-06-25T20:15:13Z",
    "severity": "HIGH"
  },
  "details": "In WhatsUp Gold versions released before 2023.1.3, an uncontrolled resource consumption vulnerability exists.\u00a0A specially crafted unauthenticated HTTP request\u00a0to the TestController Chart functionality\u00a0can lead to denial of service.",
  "id": "GHSA-67p8-jrm8-g765",
  "modified": "2024-09-07T00:31:28Z",
  "published": "2024-06-25T21:31:16Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-5011"
    },
    {
      "type": "WEB",
      "url": "https://community.progress.com/s/article/WhatsUp-Gold-Security-Bulletin-June-2024"
    },
    {
      "type": "WEB",
      "url": "https://www.progress.com/network-monitoring"
    },
    {
      "type": "WEB",
      "url": "https://www.talosintelligence.com/vulnerability_reports/TALOS-2024-1934"
    }
  ],
  "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-67XJ-XW4W-WP3Q

Vulnerability from github – Published: 2022-04-30 18:16 – Updated: 2022-04-30 18:16
VLAI
Details

Outlook Web Access (OWA) in Microsoft Exchange 2000 allows an authenticated user to cause a denial of service (CPU consumption) via a malformed OWA request for a deeply nested folder within the user's mailbox.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2001-0666"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2001-10-30T05:00:00Z",
    "severity": "LOW"
  },
  "details": "Outlook Web Access (OWA) in Microsoft Exchange 2000 allows an authenticated user to cause a denial of service (CPU consumption) via a malformed OWA request for a deeply nested folder within the user\u0027s mailbox.",
  "id": "GHSA-67xj-xw4w-wp3q",
  "modified": "2022-04-30T18:16:30Z",
  "published": "2022-04-30T18:16:30Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2001-0666"
    },
    {
      "type": "WEB",
      "url": "https://docs.microsoft.com/en-us/security-updates/securitybulletins/2001/ms01-049"
    },
    {
      "type": "WEB",
      "url": "https://exchange.xforce.ibmcloud.com/vulnerabilities/7168"
    },
    {
      "type": "WEB",
      "url": "http://www.securityfocus.com/bid/3368"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

GHSA-6827-G8XF-36C7

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

A vulnerability in danny-avila/librechat version git a1647d7 allows an unauthenticated attacker to cause a denial of service by sending a crafted payload to the server. The middleware checkBan is not surrounded by a try-catch block, and an unhandled exception will cause the server to crash. This issue is fixed in version 0.7.6.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2024-11172"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-248",
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-03-20T10:15:24Z",
    "severity": "HIGH"
  },
  "details": "A vulnerability in danny-avila/librechat version git a1647d7 allows an unauthenticated attacker to cause a denial of service by sending a crafted payload to the server. The middleware `checkBan` is not surrounded by a try-catch block, and an unhandled exception will cause the server to crash. This issue is fixed in version 0.7.6.",
  "id": "GHSA-6827-g8xf-36c7",
  "modified": "2025-03-20T12:32:41Z",
  "published": "2025-03-20T12:32:41Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-11172"
    },
    {
      "type": "WEB",
      "url": "https://github.com/danny-avila/librechat/commit/976784c01fa4cce00d4c2941801d56aed375c21b"
    },
    {
      "type": "WEB",
      "url": "https://huntr.com/bounties/c76a7ee3-2e26-45a0-8940-21c749592105"
    }
  ],
  "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-6857-HPC4-PH9X

Vulnerability from github – Published: 2022-05-13 01:23 – Updated: 2022-05-13 01:23
VLAI
Details

The try_to_unmap_cluster function in mm/rmap.c in the Linux kernel before 3.14.3 does not properly consider which pages must be locked, which allows local users to cause a denial of service (system crash) by triggering a memory-usage pattern that requires removal of page-table mappings.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2014-3122"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2014-05-11T21:55:00Z",
    "severity": "MODERATE"
  },
  "details": "The try_to_unmap_cluster function in mm/rmap.c in the Linux kernel before 3.14.3 does not properly consider which pages must be locked, which allows local users to cause a denial of service (system crash) by triggering a memory-usage pattern that requires removal of page-table mappings.",
  "id": "GHSA-6857-hpc4-ph9x",
  "modified": "2022-05-13T01:23:12Z",
  "published": "2022-05-13T01:23:12Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2014-3122"
    },
    {
      "type": "WEB",
      "url": "https://github.com/torvalds/linux/commit/57e68e9cd65b4b8eb4045a1e0d0746458502554c"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=1093076"
    },
    {
      "type": "WEB",
      "url": "http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commit%3Bh=57e68e9cd65b4b8eb4045a1e0d0746458502554c"
    },
    {
      "type": "WEB",
      "url": "http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=57e68e9cd65b4b8eb4045a1e0d0746458502554c"
    },
    {
      "type": "WEB",
      "url": "http://secunia.com/advisories/59386"
    },
    {
      "type": "WEB",
      "url": "http://secunia.com/advisories/59599"
    },
    {
      "type": "WEB",
      "url": "http://www.debian.org/security/2014/dsa-2926"
    },
    {
      "type": "WEB",
      "url": "http://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.14.3"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2014/05/01/7"
    },
    {
      "type": "WEB",
      "url": "http://www.securityfocus.com/bid/67162"
    },
    {
      "type": "WEB",
      "url": "http://www.ubuntu.com/usn/USN-2240-1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

GHSA-686W-8G4C-G9WH

Vulnerability from github – Published: 2023-09-18 06:30 – Updated: 2024-04-04 07:42
VLAI
Details

Certain WithSecure products allow a remote crash of a scanning engine via unpacking of crafted data files. This affects WithSecure Client Security 15, WithSecure Server Security 15, WithSecure Email and Server Security 15, WithSecure Elements Endpoint Protection 17 and later, WithSecure Client Security for Mac 15, WithSecure Elements Endpoint Protection for Mac 17 and later, Linux Security 64 12.0 , Linux Protection 12.0, and WithSecure Atlant (formerly F-Secure Atlant) 1.0.35-1.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2023-42520"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2023-09-18T06:15:08Z",
    "severity": "HIGH"
  },
  "details": "Certain WithSecure products allow a remote crash of a scanning engine via unpacking of crafted data files. This affects WithSecure Client Security 15, WithSecure Server Security 15, WithSecure Email and Server Security 15, WithSecure Elements Endpoint Protection 17 and later, WithSecure Client Security for Mac 15, WithSecure Elements Endpoint Protection for Mac 17 and later, Linux Security 64 12.0 , Linux Protection 12.0, and WithSecure Atlant (formerly F-Secure Atlant) 1.0.35-1.",
  "id": "GHSA-686w-8g4c-g9wh",
  "modified": "2024-04-04T07:42:56Z",
  "published": "2023-09-18T06:30:14Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-42520"
    },
    {
      "type": "WEB",
      "url": "https://www.withsecure.com/en/support/security-advisories"
    }
  ],
  "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-689P-PPGM-X7PF

Vulnerability from github – Published: 2026-06-17 18:35 – Updated: 2026-06-17 18:35
VLAI
Details

In PackageInstaller.Session#transfer of frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java, there is a possible memory exhaustion attack due to a logic error in the code. This could lead to local denial of service with no additional execution privileges needed. User interaction is not needed for exploitation.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2026-28575"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-17T13:20:15Z",
    "severity": "CRITICAL"
  },
  "details": "In PackageInstaller.Session#transfer of frameworks/base/services/core/java/com/android/server/pm/PackageInstallerSession.java, there is a possible memory exhaustion attack due to a logic error in the code. This could lead to local denial of service with no additional execution privileges needed. User interaction is not needed for exploitation.",
  "id": "GHSA-689p-ppgm-x7pf",
  "modified": "2026-06-17T18:35:48Z",
  "published": "2026-06-17T18:35:48Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-28575"
    },
    {
      "type": "WEB",
      "url": "https://source.android.com/docs/security/bulletin/android-17"
    }
  ],
  "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"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/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-68HH-P8M2-HPX3

Vulnerability from github – Published: 2023-09-27 18:30 – Updated: 2024-01-25 18:30
VLAI
Details

A vulnerability in the networking component of Cisco access point (AP) software could allow an unauthenticated, remote attacker to cause a temporary disruption of service.

This vulnerability is due to overuse of AP resources. An attacker could exploit this vulnerability by connecting to an AP on an affected device as a wireless client and sending a high rate of traffic over an extended period of time. A successful exploit could allow the attacker to cause the Datagram TLS (DTLS) session to tear down and reset, causing a denial of service (DoS) condition.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2023-20176"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2023-09-27T18:15:10Z",
    "severity": "HIGH"
  },
  "details": "A vulnerability in the networking component of Cisco access point (AP) software could allow an unauthenticated, remote attacker to cause a temporary disruption of service.\n\n This vulnerability is due to overuse of AP resources. An attacker could exploit this vulnerability by connecting to an AP on an affected device as a wireless client and sending a high rate of traffic over an extended period of time. A successful exploit could allow the attacker to cause the Datagram TLS (DTLS) session to tear down and reset, causing a denial of service (DoS) condition.",
  "id": "GHSA-68hh-p8m2-hpx3",
  "modified": "2024-01-25T18:30:44Z",
  "published": "2023-09-27T18:30:28Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-20176"
    },
    {
      "type": "WEB",
      "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-click-ap-dos-wdcXkvnQ"
    }
  ],
  "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-68HX-HV9V-7V3W

Vulnerability from github – Published: 2023-11-08 18:30 – Updated: 2024-09-04 15:30
VLAI
Details

In Helix Core versions prior to 2023.2, an unauthenticated remote Denial of Service (DoS) via the buffer was identified. Reported by Jason Geffner.  

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2023-5759"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2023-11-08T16:15:11Z",
    "severity": "HIGH"
  },
  "details": "In Helix Core versions prior to 2023.2, an unauthenticated remote Denial of Service (DoS) via the buffer was identified.  Reported by Jason Geffner. \u00a0\n",
  "id": "GHSA-68hx-hv9v-7v3w",
  "modified": "2024-09-04T15:30:31Z",
  "published": "2023-11-08T18:30:31Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-5759"
    },
    {
      "type": "WEB",
      "url": "https://perforce.com"
    }
  ],
  "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-68P2-8VQP-FWX7

Vulnerability from github – Published: 2026-04-21 15:32 – Updated: 2026-04-22 00:31
VLAI
Details

Denial-of-service in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 150.

Show details on source website

{
  "affected": [],
  "aliases": [
    "CVE-2026-6781"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-21T13:16:23Z",
    "severity": "HIGH"
  },
  "details": "Denial-of-service in the Audio/Video: Playback component. This vulnerability was fixed in Firefox 150.",
  "id": "GHSA-68p2-8vqp-fwx7",
  "modified": "2026-04-22T00:31:39Z",
  "published": "2026-04-21T15:32:22Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-6781"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=2025583"
    },
    {
      "type": "WEB",
      "url": "https://www.mozilla.org/security/advisories/mfsa2026-30"
    },
    {
      "type": "WEB",
      "url": "https://www.mozilla.org/security/advisories/mfsa2026-33"
    }
  ],
  "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-68P4-95XF-7GX8

Vulnerability from github – Published: 2023-07-28 15:36 – Updated: 2023-07-28 15:36
VLAI
Summary
Denial of service from large image
Details

Impact

An high-privileged user could create a Package referencing an arbitrarily large image containing that Crossplane would then parse, possibly resulting in exhausting all the available memory and therefore in the container being OOMKilled.

The impact is low due to the high privileges required to be able to create the Package and the eventually consistency nature of controller.

Patches

The problem has been fixed in 1.11.5, 1.12.3 and 1.13.0, all the supported versions of Crossplane at the time of writing.

Workarounds

Only using images from trusted sources and keeping Package editing/creating privileges to administrators only, which should be both considered already best practices.

References

See ADA-XP-23-16 in the Security Audit's report.

Credits

This was reported as ADA-XP-23-16 by @AdamKorcz and @DavidKorczynski from Ada Logic and facilitated by OSTIF as part of the Security Audit sponsored by CNCF.

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/crossplane/crossplane"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.11.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/crossplane/crossplane"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.12.0"
            },
            {
              "fixed": "1.12.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-37900"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2023-07-28T15:36:08Z",
    "nvd_published_at": "2023-07-27T16:15:10Z",
    "severity": "LOW"
  },
  "details": "### Impact\n\nAn high-privileged user could create a Package referencing an arbitrarily large image containing that Crossplane would then parse, possibly resulting in exhausting all the available memory and therefore in the container being OOMKilled.\n\nThe impact is low due to the high privileges required to be able to create the Package and the eventually consistency nature of controller.\n\n### Patches\n\nThe problem has been fixed in 1.11.5, 1.12.3 and 1.13.0, all the supported versions of Crossplane at the time of writing.\n\n### Workarounds\n\nOnly using images from trusted sources and keeping Package editing/creating privileges to administrators only, which should be both considered already best practices.\n\n### References\n\nSee `ADA-XP-23-16` in the Security Audit\u0027s [report](https://github.com/crossplane/crossplane/blob/ac8b24fe739c5d942ea885157148497f196c3dd3/security/ADA-security-audit-23.pdf).\n\n### Credits\n\nThis was reported as `ADA-XP-23-16` by @AdamKorcz and @DavidKorczynski from Ada Logic and facilitated by OSTIF as part of the Security Audit sponsored by CNCF.",
  "id": "GHSA-68p4-95xf-7gx8",
  "modified": "2023-07-28T15:36:08Z",
  "published": "2023-07-28T15:36:08Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/crossplane/crossplane/security/advisories/GHSA-68p4-95xf-7gx8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-37900"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/crossplane/crossplane"
    },
    {
      "type": "WEB",
      "url": "https://github.com/crossplane/crossplane/blob/ac8b24fe739c5d942ea885157148497f196c3dd3/security/ADA-security-audit-23.pdf"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Denial of service from large image"
}

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.