CVE-2021-41773: Apache HTTP Server Path Traversal Vulnerability

Recommended actionPatch now

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

Patch available

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. The original patch issued under this CVE ID is insufficient, please review remediation information under CVE-2021-42013.

What

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

Why

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

How

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

Official authority intelligence

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

ENISA EUVD · EUVD-2021-28781Known-exploited evidence recorded

A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. 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 is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found to be incomplete, see CVE-2021-42013.

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 ↗

Canadian Centre for Cyber Security · English · AV21-495Apache security advisory – update 1

On 4 October 2021 Apache published a Security Bulletin to address vulnerabilities in the following product: UPDATE 1

Official advisory ↗

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

ord?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=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=

Official advisory ↗

CERT-FR · French · CERTFR-2021-AVI-759Multiples vulnérabilités dans Apache HTTP Server

De multiples vulnérabilités ont été découvertes dans Apache HTTP Server. Elles permettent à un attaquant de provoquer un déni de service à distance, une atteinte à l'intégrité des données et une atteinte à la confidentialité des données. La vulnérabilité CVE-2021-41773 est activement exploitée et de nombreux codes d'exploitation sont publiquement disponibles sur Internet.

Official advisory ↗

NBSZ-NKI · Hungarian · cve-2021-41773CVE-2021-41773

Magas

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 ↗

JVN iPedia · Japanese · JVNDB-2021-002868Apache HTTP Server 2.4 における複数の脆弱性に対するアップデート

The Apache Software Foundation から、Apache HTTP Server 2.4 系における次の複数の脆弱性に対応した Apache HTTP Server 2.4.50 が公開されました。　* HTTP/2 リクエストの処理における、NULL ポインタ参照の脆弱性 - CVE-2021-41524 　* パスの正規化処理の欠陥による、パストラバーサルの脆弱性 - CVE-2021-41773

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, BIG-IQ의 iControl REST 인터페이스에서 발생하는 원격 코드 실행 취약점(CVE-2021-22986)[12] ㅇ Grafana 소프트웨어에서

Official advisory ↗

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

#### Apache HTTP Server 보안 업데이트 권고 2021.10.08 ##### □ 개요 o Apache 소프트웨어 재단은 자사의 HTTP Server에서 발생하는 취약점을 해결한 보안 업데이트 발표 [1] o 기존 CVE-2021-41773 취약점을 해결하는 보안 패치에서 취약점이 재차 확인되어, 이를 보완하는 업데이트 파일 공개 ##### □ 설명 o Apache HTTP Server에서 경로 탐색(Path Traversal)으로 인해 발생하는 정보노출 취약점(CVE-2021-42013) ##### □ 영향을 받는 제품 및 최신 버전 제품 영향받는 버전 최신 버전 Apache HTTP Server 2.4.49, 2.4.50 버전 (이전 버전은 영향받지 않음) 2.4.51 버전 o 제조사 홈페이지를 통해 최신 버전으로 업데이트 적용 [2] ##### □ 기타 문의사항 o 한국인터넷진흥원 사이버민원센터: 국번 없이 118 [참고사이트] [1] https://httpd.apache.org/security/vulnerabilities_24.html [2] https://httpd.apache.org/download.cgi ##### □ 작성 : 침해사고분석단 취약점분석팀

Official advisory ↗

KISA KrCERT/CC · Korean · KNVD-5407Apache HTTP Server 보안 업데이트 권고

Apache HTTP Server에서 경로 탐색(Path Traversal)으로 인해 발생하는 정보노출 취약점(CVE-2021-41773)

Official advisory ↗

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 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.

Evidence and provenance

Published 5 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-2021-28781

Product sourceCNA

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 ↗

21 Oct 2025, 23:25 UTC
Affected versionsThe structured affected or fixed version information changed.
Before
Apache HTTP Server 2.4 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.
After
Apache HTTP Server: Apache HTTP Server 2.4 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.
CNA ↗

2021-10-05CVE published

2021-11-03Added to CISA KEV

2025-10-21Fixed release or patch reference recorded

ENISA EUVD · EUVD-2021-28781↗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.

Apache HTTP Server Path Traversal Vulnerability

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

ENISA European Vulnerability Database

EUVD-2021-28781

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

What changed after publication

Apache HTTP Server Path Traversal Vulnerability

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

EUVD-2021-28781

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

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