BlackTreeCVE Intelligence
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Full vulnerability report · 2021
CVE-2021-3803High confidence

Inefficient Regular Expression Complexity in fb55/nth-check

fb55 · fb55/nth-check

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 3 Aug 2024

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 2.21% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs fb55 fb55/nth-check and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

4 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcenode-nth-checkVendor fix publishedDebian records a fixed source-package version for this release.2.0.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcenode-nth-checkVendor fix publishedDebian records a fixed source-package version for this release.2.0.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcenode-nth-checkVendor fix publishedDebian records a fixed source-package version for this release.2.0.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcenode-nth-checkVendor fix publishedDebian records a fixed source-package version for this release.2.0.1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-2109

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

nth-check is vulnerable to Inefficient Regular Expression Complexity

What

nth-check is vulnerable to Inefficient Regular Expression Complexity

Why

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

nth-check is vulnerable to Inefficient Regular Expression Complexity

Why

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Inefficient Regular Expression Complexity → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-1333 ↗

CWE-1333: Inefficient Regular Expression Complexity. The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-1333Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-1955Atlassian Bamboo, Bitbucket, Confluence, Fisheye, Crucible, Jira und Jira Service Management: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Atlassian Bamboo, Bitbucket, Confluence, Fisheye, Crucible, Jira und Jira Service Management ausnutzen, um beliebigen Code auszuführen, erweiterte Berechtigungen zu erlangen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand auszulösen.

Official advisory ↗
BSI · German · WID-SEC-2023-2229Splunk Splunk Enterprise: Mehrere Schwachstellen

Ein entfernter, authentifizierter Angreifer kann mehrere Schwachstellen in Splunk Splunk Enterprise ausnutzen, um beliebigen Code auszuführen, einen 'Denial of Service'-Zustand zu verursachen, seine Privilegien zu erweitern und weitere, nicht spezifizierte Auswirkungen zu verursachen.

Official advisory ↗
BSI · German · WID-SEC-2024-1591Juniper JUNOS: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Juniper JUNOS ausnutzen, um einen Denial of Service zu verursachen, Informationen offenzulegen, Privilegien zu erweitern und Sicherheitsmechanismen inklusive zu umgehen.

Official advisory ↗
BSI · German · WID-SEC-2023-1350Splunk Splunk Enterprise: Mehrere Schwachstellen in Komponenten von Drittanbietern

Ein Angreifer kann mehrere Schwachstellen in Splunk Splunk Enterprise in diversen Komponenten von Drittanbietern ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210922Security Bulletin 22 Sep 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 Sep 2021, published on 22 September 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0773Multiples vulnérabilités dans les produits Atlassian

6835 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26835 Bulletin de sécurité Atlassian JSWSERVER-26836 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26836 Bulletin de sécurité Atlassian JSWSERVER-26837 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26837 Bulletin de sécurité Atlassian JSWSERVER-26838 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26838 Bulletin de sécurité Atlassian JSWSERVER-26840 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26840 Bulletin de sécurité Atlassian JSWSERVER-26841 du 16 juin 2026 https://jira.atlassian.com/browse/JSWSERVER-26841 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2026-26996 https://www.cve.org/CVERecord?id=CVE-2026-26996 Référence CVE CVE-2026-27903 https://www.cve.org/CVERecord?id=CVE-2026-27903 Référence CVE CVE-2026-27904 https://www.cve.org/CVERecord?id=CVE-2026-27904 Référence CVE CVE-2026-29129 https://www.cve.org/CVERecord?id=CVE-2026-29129 Référence CVE CVE-2026-33870 https://www.cve.org/CVERecord?id=CVE-2026-33870 Référence CVE CVE-2026-33871 https://www.cve.org/CVERecord?id=CVE-2026-33871 Référence CVE CVE-2026-34077 https://www.cve.org/CVERecord?id=CVE-2026-34077 Référence CVE CVE-2026-34486 https://www.cve.org/CVERecord?id=C

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0923Multiples vulnérabilités dans les produits IBM

d?id=CVE-2018-12545 Référence CVE CVE-2019-10241 https://www.cve.org/CVERecord?id=CVE-2019-10241 Référence CVE CVE-2019-13224 https://www.cve.org/CVERecord?id=CVE-2019-13224 Référence CVE CVE-2019-16163 https://www.cve.org/CVERecord?id=CVE-2019-16163 Référence CVE CVE-2019-19012 https://www.cve.org/CVERecord?id=CVE-2019-19012 Référence CVE CVE-2020-15168 https://www.cve.org/CVERecord?id=CVE-2020-15168 Référence CVE CVE-2020-27216 https://www.cve.org/CVERecord?id=CVE-2020-27216 Référence CVE CVE-2021-28169 https://www.cve.org/CVERecord?id=CVE-2021-28169 Référence CVE CVE-2021-34428 https://www.cve.org/CVERecord?id=CVE-2021-34428 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2021-40690 https://www.cve.org/CVERecord?id=CVE-2021-40690 Référence CVE CVE-2021-43138 https://www.cve.org/CVERecord?id=CVE-2021-43138 Référence CVE CVE-2021-44906 https://www.cve.org/CVERecord?id=CVE-2021-44906 Référence CVE CVE-2022-0144 https://www.cve.org/CVERecord?id=CVE-2022-0144 Référence CVE CVE-2022-0235 https://www.cve.org/CVERecord?id=CVE-2022-0235 Référence CVE CVE-2022-24735 https://www.cve.org/CVERecord?id=CVE-2022-24735 Référence CVE CVE-2022-24736 https://www.cve.org/CVERecord?id=CVE-2022-24736 Référence CVE CVE-2022-24834 https://www.cve.org/CVERecord?id=CVE-2

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0575Multiples vulnérabilités dans les produits Juniper Networks

rd?id=CVE-2021-3347 Référence CVE CVE-2021-33909 https://www.cve.org/CVERecord?id=CVE-2021-33909 Référence CVE CVE-2021-34798 https://www.cve.org/CVERecord?id=CVE-2021-34798 Référence CVE CVE-2021-35604 https://www.cve.org/CVERecord?id=CVE-2021-35604 Référence CVE CVE-2021-35624 https://www.cve.org/CVERecord?id=CVE-2021-35624 Référence CVE CVE-2021-36160 https://www.cve.org/CVERecord?id=CVE-2021-36160 Référence CVE CVE-2021-37701 https://www.cve.org/CVERecord?id=CVE-2021-37701 Référence CVE CVE-2021-37712 https://www.cve.org/CVERecord?id=CVE-2021-37712 Référence CVE CVE-2021-37713 https://www.cve.org/CVERecord?id=CVE-2021-37713 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2021-39275 https://www.cve.org/CVERecord?id=CVE-2021-39275 Référence CVE CVE-2021-40438 https://www.cve.org/CVERecord?id=CVE-2021-40438 Référence CVE CVE-2021-41524 https://www.cve.org/CVERecord?id=CVE-2021-41524 Référence CVE CVE-2021-41773 https://www.cve.org/CVERecord?id=CVE-2021-41773 Référence CVE CVE-2021-42013 https://www.cve.org/CVERecord?id=CVE-2021-42013 Référence CVE CVE-2021-43527 https://www.cve.org/CVERecord?id=CVE-2021-43527 Référence CVE CVE-2021-44224 https://www.cve.org/CVERecord?id=CVE-2021-44224 Référence CVE CVE-2021-44790 https://www.cve.org/CVERecord?id=C

Official advisory ↗
CERT-FR · French · CERTFR-2023-AVI-0705Multiples vulnérabilités dans les produits IBM

1 août 2023 https://www.ibm.com/support/pages/node/7029765 Bulletin de sécurité IBM 7029766 du 31 août 2023 https://www.ibm.com/support/pages/node/7029766 Bulletin de sécurité IBM 7029864 du 31 août 2023 https://www.ibm.com/support/pages/node/7029864 Référence CVE CVE-2020-13936 https://www.cve.org/CVERecord?id=CVE-2020-13936 Référence CVE CVE-2020-28498 https://www.cve.org/CVERecord?id=CVE-2020-28498 Référence CVE CVE-2021-23440 https://www.cve.org/CVERecord?id=CVE-2021-23440 Référence CVE CVE-2021-33813 https://www.cve.org/CVERecord?id=CVE-2021-33813 Référence CVE CVE-2021-37699 https://www.cve.org/CVERecord?id=CVE-2021-37699 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2021-43803 https://www.cve.org/CVERecord?id=CVE-2021-43803 Référence CVE CVE-2022-25858 https://www.cve.org/CVERecord?id=CVE-2022-25858 Référence CVE CVE-2022-25883 https://www.cve.org/CVERecord?id=CVE-2022-25883 Référence CVE CVE-2022-32212 https://www.cve.org/CVERecord?id=CVE-2022-32212 Référence CVE CVE-2022-32213 https://www.cve.org/CVERecord?id=CVE-2022-32213 Référence CVE CVE-2022-32214 https://www.cve.org/CVERecord?id=CVE-2022-32214 Référence CVE CVE-2022-32215 https://www.cve.org/CVERecord?id=CVE-2022-32215 Référence CVE CVE-2022-32222 https://www.cve.org/CVERecord?id=C

Official advisory ↗
CERT-FR · French · CERTFR-2023-AVI-0701Multiples vulnérabilités dans Splunk

ecord?id=CVE-2021-33195 Référence CVE CVE-2021-33196 https://www.cve.org/CVERecord?id=CVE-2021-33196 Référence CVE CVE-2021-33197 https://www.cve.org/CVERecord?id=CVE-2021-33197 Référence CVE CVE-2021-33198 https://www.cve.org/CVERecord?id=CVE-2021-33198 Référence CVE CVE-2021-34558 https://www.cve.org/CVERecord?id=CVE-2021-34558 Référence CVE CVE-2021-3520 https://www.cve.org/CVERecord?id=CVE-2021-3520 Référence CVE CVE-2021-3572 https://www.cve.org/CVERecord?id=CVE-2021-3572 Référence CVE CVE-2021-36221 https://www.cve.org/CVERecord?id=CVE-2021-36221 Référence CVE CVE-2021-36976 https://www.cve.org/CVERecord?id=CVE-2021-36976 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2021-38297 https://www.cve.org/CVERecord?id=CVE-2021-38297 Référence CVE CVE-2021-38561 https://www.cve.org/CVERecord?id=CVE-2021-38561 Référence CVE CVE-2021-39293 https://www.cve.org/CVERecord?id=CVE-2021-39293 Référence CVE CVE-2021-41182 https://www.cve.org/CVERecord?id=CVE-2021-41182 Référence CVE CVE-2021-41183 https://www.cve.org/CVERecord?id=CVE-2021-41183 Référence CVE CVE-2021-41184 https://www.cve.org/CVERecord?id=CVE-2021-41184 Référence CVE CVE-2021-41771 https://www.cve.org/CVERecord?id=CVE-2021-41771 Référence CVE CVE-2021-41772 https://www.cve.org/CVERecord?id=C

Official advisory ↗
CERT-FR · French · CERTFR-2023-AVI-0428Multiples vulnérabilités dans les produits Splunk

ord?id=CVE-2021-23382 Référence CVE CVE-2021-27292 https://www.cve.org/CVERecord?id=CVE-2021-27292 Référence CVE CVE-2021-29060 https://www.cve.org/CVERecord?id=CVE-2021-29060 Référence CVE CVE-2021-31566 https://www.cve.org/CVERecord?id=CVE-2021-31566 Référence CVE CVE-2021-33502 https://www.cve.org/CVERecord?id=CVE-2021-33502 Référence CVE CVE-2021-33503 https://www.cve.org/CVERecord?id=CVE-2021-33503 Référence CVE CVE-2021-33587 https://www.cve.org/CVERecord?id=CVE-2021-33587 Référence CVE CVE-2021-3520 https://www.cve.org/CVERecord?id=CVE-2021-3520 Référence CVE CVE-2021-36976 https://www.cve.org/CVERecord?id=CVE-2021-36976 Référence CVE CVE-2021-3803 https://www.cve.org/CVERecord?id=CVE-2021-3803 Référence CVE CVE-2021-43565 https://www.cve.org/CVERecord?id=CVE-2021-43565 Référence CVE CVE-2022-1705 https://www.cve.org/CVERecord?id=CVE-2022-1705 Référence CVE CVE-2022-1962 https://www.cve.org/CVERecord?id=CVE-2022-1962 Référence CVE CVE-2022-22576 https://www.cve.org/CVERecord?id=CVE-2022-22576 Référence CVE CVE-2022-23491 https://www.cve.org/CVERecord?id=CVE-2022-23491 Référence CVE CVE-2022-23772 https://www.cve.org/CVERecord?id=CVE-2022-23772 Référence CVE CVE-2022-23773 https://www.cve.org/CVERecord?id=CVE-2022-23773 Référence CVE CVE-2022-23806 https://www.cve.org/CVERecord?id=CVE-2

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-012196nth-check における脆弱性

nth-check には、不特定の脆弱性が存在します。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
fb55/nth-check: unspecified < 2.0.1
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
Official vendor articles1 stored document

Linked articles are downloaded and versioned as source evidence. A CVE mention or approved update relationship does not, by itself, verify a fix for every product branch.

04

Evidence and provenance

Published 17 Sept 2021 · Last source change 3 Aug 2024, 17:09 UTC · CWE-1333 · Inefficient Regular Expression Complexity

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-2109
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-2109↗Public exploit reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-3803 · cve.blacktree.nl