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Full vulnerability report · 2021
CVE-2021-42013High confidence

Apache HTTP Server Path Traversal Vulnerability

Apache · HTTP Server

9.8CriticalCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • CISA confirms exploitation in the wild.
  • 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 99.96% 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 Apache HTTP Server 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

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

7 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
Alpine v3.23v3.23 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.51-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.51-r0Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.21v3.21 · mainapache2Vendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.51-r0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.51-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.51-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.51-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourceapache2Vendor fix publishedDebian records a fixed source-package version for this release.2.4.51-1Debian Security Tracker ↗Source updated 5 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-2021-29001

CISA KEV mirrored by ENISA

It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 3 Nov 2021. Evidence sources: cisa_kev.
ENISA score
9.8 · CVSS 3.1
Advisory evidence
2 linked advisory records
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
01

What, why and how

Apache HTTP Server contains a path traversal vulnerability that allows an attacker to perform remote code execution if files outside directories configured by Alias-like directives are not under default require all denied or if CGI scripts are enabled. This CVE ID resolves an incomplete patch for CVE-2021-41773.

What

Apache HTTP Server contains a path traversal vulnerability that allows an attacker to perform remote code execution if files outside directories configured by Alias-like directives are not under default require all denied or if CGI scripts are enabled. This CVE ID resolves an incomplete patch for CVE-2021-41773.

Why

Attacker-controlled path data is not constrained to the intended directory before the application accesses a file.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

What

Apache HTTP Server contains a path traversal vulnerability that allows an attacker to perform remote code execution if files outside directories configured by Alias-like directives are not under default require all denied or if CGI scripts are enabled. This CVE ID resolves an incomplete patch for CVE-2021-41773.

Why

Attacker-controlled path data is not constrained to the intended directory before the application accesses a file.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.

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.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2021-11-03. Known ransomware campaign use is recorded.

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 → Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') → execute code or commands in the affected security context
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-22 ↗

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'). The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

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:H/I:H/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.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
NetworkUnauthenticatedRemote code executionCWE-22CISA KEVPublic exploit reference
A

Official authority intelligence

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

ENISA EUVD · EUVD-2021-29001Known-exploited evidence recorded

It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache 2.4.50 and not earlier versions.

Official EUVD record ↗
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 ↗
Cyber Security Agency of Singapore · English · CSA-SB-20211013Security Bulletin 13 Oct 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 13 Oct 2021, published on 13 October 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

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

ord?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=CVE-2021-44790 Référence CVE CVE-2021-44906 https://www.cve.org/CVERecord?id=CVE-2021-44906 Référence CVE CVE-2022-21245 https://www.cve.org/CVERecord?id=CVE-2022-21245 Référence CVE CVE-2022-21270 https://www.cve.org/CVERecord?id=CVE-2022-21270 Référence CVE CVE-2022-21303 https://www.cve.org/CVERecord?id=CVE-2022-21303 Référence CVE CVE-2022-21304 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-764Vulnérabilité dans Apache HTTP Server

Une vulnérabilité a été découverte dans Apache HTTP Server. Elle permet à un attaquant de provoquer une exécution de code arbitraire à distance et une atteinte à la confidentialité des données.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-000090Apache HTTP Server におけるディレクトリトラバーサルの脆弱性

The Apache Software Foundation が提供する Apache HTTP Server には、ディレクトリトラバーサル (CWE-22) の脆弱性が存在します。 この脆弱性情報は、次の方が製品開発者に直接報告し、製品開発者との調整を経て、製品利用者への周知を目的に JVN での公表に至りました。 報告者: 株式会社インターネットイニシアティブ 熊坂駿吾 氏

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5873최근 해킹 공격에 활용되는 취약점 보안 업데이트 권고

#### 최근 해킹 공격에 활용되는 취약점 보안 업데이트 권고 2023.02.17 ##### □ 개요 o 최근 기업에서 운영 중인 서버의 취약점을 악용한 해킹 툴 제작 및 공격이 활발히 발생하고있어, 기업 담당자들의 철저한 사전 보안 점검 및 대비 필요 o 취약한 버전의 소프트웨어, 서버를 사용하는 기업 및 사용자는 최신버전으로 업데이트 권고 ##### □ 최근 악용되고있는 주요 취약점 ㅇ Apache APISIX에서 발생하는 인증 우회 취약점(CVE-2021-45232)[1] ㅇ Apache HTTP Server에서 경로 탐색(Path Traversal)으로 인해 발생하는 정보노출 취약점(CVE-2021-42013)[2] ㅇ Apache HTTP Server에서 경로 탐색(Path Traversal)으로 인해 발생하는 정보노출 취약점(CVE-2021-41773)[3] ㅇ Apache OFBiz에서 발생하는 크로스 사이트 스크립팅(XSS) 취약점(CVE-2020-9496)[4] ㅇ Apache OFBiz에서 발생하는 역직렬화 취약점(CVE-2021-26295)[5] ㅇ Apache Struts에서 발생하는 원격코드 실행 취약점(CVE-2020-17530)[6] ㅇ Apache Struts에서 사용자 입력값 검증 미흡으로 발생하는 원격 코드 실행 취약점(CVE-2021-31805)[7] ㅇ Apache Tomcat이 AJP request 메시지를 처리할 때, 메시지에 대한 처리가 미흡하여 발생하는 원격코드실행 취약점(CVE-2020-1938)[8] ㅇ Apache Log4j에서 발생하는 원격코드 실행 취약점(CVE-2021-44228)[9] ㅇ Atlassian Confluence Server 및 Data Center에서 OGNL 인젝션으로 인해 발생하는 원격코드실행 취약점(CVE-2021-26084)[10] ㅇ BIG-IP에서 iControl REST 인증 미흡으로 인해 발생하는 불충분한 인가 취약점(CVE-2022-1388)[11] ㅇ BIG-IP, BI

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5405Apache HTTP Server 보안 업데이트 권고

Apache HTTP Server에서 경로 탐색(Path Traversal)으로 인해 발생하는 정보노출 취약점(CVE-2021-42013)

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
Apache HTTP Server: Apache HTTP Server 2.4.50, Apache HTTP Server 2.4.49
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.
04

Evidence and provenance

Published 7 Oct 2021 · Last source change 21 Oct 2025, 23:25 UTC · CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

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-2021-29001
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched

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

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    Apache HTTP Server 2.4.49; Apache HTTP Server 2.4.50 · 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.
    After
    Apache HTTP Server: Apache HTTP Server 2.4.49, Apache HTTP Server 2.4.50 · 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.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-29001↗CISA KEV record↗CVE authority or vendor reference↗Patch or update reference↗Patch or update reference↗Patch or update reference↗Public exploit reference↗Public exploit reference↗Official CVE record (CNA and ADP data)↗
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-2021-42013 · cve.blacktree.nl