PatchTheCVECVE-2021-42013: Apache HTTP Server Path Traversal Vulnerability
100
Patch now
CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTDOWNGRADEMITIGATEDOWNGRADE
CVE-2021-42013 is a critical-severity flaw (CVSS 9.8) affecting http server, fedora, instantis enterprisetrack, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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 cod
Why this priority
- Critical severity
- EPSS top 1%: very likely to be exploited
- Exploited in the wild (CISA KEV)
- Used in ransomware campaigns
- Public exploit reference
- CISA SSVC: automatable with total technical impact
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.8 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 100.0% (top 1%) |
| CISA exploited list | Yes, fix due 2021-11-17, used in ransomware |
| Weakness | CWE-22 |
| Published | 2021-10-07 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Exploited Added to the CISA Known Exploited Vulnerabilities list
- Deadline CISA due date for US federal agencies to patch
- Updated Record last modified
apache http server DOWNGRADE
Affected: 2.4.49 · 2.4.50
Fixed in: no fixed release known
Safe to downgrade to: a release before 2.4.49
1. Check installed version
apt-cache policy http-server || rpm -q http-server || http-server --version
2. No fixed release: DOWNGRADE to a release before 2.4.49 (Debian / Ubuntu)
apt-cache madison http-server
sudo apt install http-server=<VERSION_BEFORE_2.4.49>
sudo apt-mark hold http-server
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list http-server
sudo dnf downgrade http-server-<VERSION_BEFORE_2.4.49>
sudo dnf versionlock add http-server
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
fedoraproject fedora MITIGATE
Affected: 34 · 35
Fixed in: no fixed release known
Safe to downgrade to: a release before 34
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
oracle instantis enterprisetrack DOWNGRADE
Affected: 17.1 · 17.2 · 17.3
Fixed in: no fixed release known
Safe to downgrade to: a release before 17.1
1. Check installed version
apt-cache policy instantis-enterprisetrack || rpm -q instantis-enterprisetrack || instantis-enterprisetrack --version
2. No fixed release: DOWNGRADE to a release before 17.1 (Debian / Ubuntu)
apt-cache madison instantis-enterprisetrack
sudo apt install instantis-enterprisetrack=<VERSION_BEFORE_17.1>
sudo apt-mark hold instantis-enterprisetrack
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list instantis-enterprisetrack
sudo dnf downgrade instantis-enterprisetrack-<VERSION_BEFORE_17.1>
sudo dnf versionlock add instantis-enterprisetrack
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
oracle jd edwards enterpriseone tools UPGRADE
Affected: < 9.2.6.0
Fixed in: 9.2.6.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy jd-edwards-enterpriseone-tools || rpm -q jd-edwards-enterpriseone-tools || jd-edwards-enterpriseone-tools --version
2. UPGRADE to 9.2.6.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade jd-edwards-enterpriseone-tools
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade jd-edwards-enterpriseone-tools
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
oracle secure backup UPGRADE
Affected: < 18.1.0.1.0
Fixed in: 18.1.0.1.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy secure-backup || rpm -q secure-backup || secure-backup --version
2. UPGRADE to 18.1.0.1.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade secure-backup
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade secure-backup
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
netapp cloud backup MITIGATE
Affected: all versions
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy cloud-backup || rpm -q cloud-backup || cloud-backup --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.
Exact fixes by distribution
A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · bitcoin-core-selinux · FIXED · 0.3-2.fc46 · FEDORA-2026-51fc806272 · source
sudo dnf upgrade --advisory=FEDORA-2026-51fc806272
Fedora ELN · guestfs-tools · FIXED · 1.57.5-1.eln159 · FEDORA-2026-9577c5ec16 · source
sudo dnf upgrade --advisory=FEDORA-2026-9577c5ec16
Ubuntu 22.04 · apache2 · NOT AFFECTED
Ubuntu 20.04 · apache2 · NOT AFFECTED
Debian 12 · apache2 · FIXED · 2.4.51-1
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.51-1" && echo PATCHED || echo STILL-VULNERABLE
Debian 13 · apache2 · FIXED · 2.4.51-1
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.51-1" && echo PATCHED || echo STILL-VULNERABLE
RHEL 6 · httpd · NOT AFFECTED
RHEL 7 · httpd · NOT AFFECTED
RHEL 8 · httpd:2.4/httpd · NOT AFFECTED
RHEL 9 · httpd · NOT AFFECTED
Alpine 3.20 · apache2 · FIXED · apache2-2.4.51-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.21 · apache2 · FIXED · apache2-2.4.51-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.22 · apache2 · FIXED · apache2-2.4.51-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.23 · apache2 · FIXED · apache2-2.4.51-r0
apk add --upgrade apache2
apk info -v apache2
sudo yum update --advisory=ALAS2-2021-1716
sudo yum update --advisory=ALAS-2021-1543
Public exploits and detection
Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.
- GitHub PoC: walnutsecurity/cve-2021-42013 (30 stars)
- GitHub PoC: Vulnmachines/cve-2021-42013 (15 stars)
- Exploit-DB: Apache HTTP Server 2.4.50 - Path Traversal & Remote Code Execution (RCE)
- Exploit-DB: Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (2)
- Exploit-DB: Apache HTTP Server 2.4.50 - Remote Code Execution (RCE) (3)
- Metasploit: Apache 2.4.49/2.4.50 Traversal RCE scanner
- Metasploit: Apache 2.4.49/2.4.50 Traversal RCE
- Nuclei scan template: Apache 2.4.49/2.4.50 - Path Traversal and Remote Code Execution
Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2021-42013?
http server: downgrade or apply the listed mitigation; fedora: mitigate or apply the listed mitigation; instantis enterprisetrack: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-42013 being exploited?
Yes. CVE-2021-42013 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.
What does CVE-2021-42013 affect?
CVE-2021-42013 affects http server, fedora, instantis enterprisetrack. Severity is critical (CVSS 9.8). 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
How urgent is CVE-2021-42013?
Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Apache HTTP Server vulnerabilities
Related CVEs
- CVE-2026-34291 HIGH 8.7 DOWNGRADE Vulnerability in the Oracle HTTP Server product of Oracle Fusion Middleware (component: Core)
- CVE-2026-23918 HIGH 8.8 DOWNGRADE Double Free and possible RCE vulnerability in Apache HTTP Server with the HTTP/2 protocol. This issue affects
- CVE-2026-24072 HIGH 8.8 UPGRADE An escalation of privilege bug in various modules in Apache HTTP 2.4.66 and earlier allows local .htaccess aut
- CVE-2026-34059 HIGH 7.5 UPGRADE Buffer Over-read vulnerability in Apache HTTP Server. This issue affects Apache HTTP Server: through 2.4.66.
- CVE-2026-33523 MEDIUM 6.5 UPGRADE HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised bac